3-46 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
be the result of preventing surface disturbance in these areas or within 650 feet
6 Typically the nesting season is when avian species are most sensitive to disturbance which generally occurs from
3 Affected Environment and Environmental Consequences
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 3-47
Canals used for water delivery or drainage on Reclamation lands would be
avoided by a 100-foot no surface occupancy buffer This would minimize impacts
from noise or visual disturbances on migratory birds inhabiting these areas
The impacts on migratory bird species from noxious weed establishment and
spread would be the same as those described for general wildlife species in
Section 37 Wildlife and Key Habitat
Further the project proponents would apply additional applicable environmental
protection measures and best management practices as described in Appendix
E of the Salt Wells EIS (BLM 2011a) to the Proposed Action These measures
are included in Appendix C of this EA These measures would reduce or avoid
impacts on migratory birds and their habitat by taking the following measures
Providing environmental education for workers
Preventing overland travel
Minimizing vegetation removal
Implementing measures to prevent wildlife entrapment or injury
Minimizing or preventing weed establishment and spread in
migratory bird habitat including the adjacent IBA
No Action Alternative
Under the No Action Alternative the BLM and Navy would not implement the
Proposed Action on federal lands None
of the potential environmental impacts
associated with the Proposed Action
would occur
310 INVASIVE NONNATIVE AND NOXIOUS WEED
SPECIES
3101 Affected Environment
To characterize the affected environment
for invasive nonnative and noxious weed
species the BLM reviewed information
relevant to the project area including
Section 310 Invasive Nonnative Species
(page 3-92) of the Salt Wells EIS (BLM
2011a) and the NAS Fallon Integrated
Natural Resources Management Plan
(NAS Fallon 2014) Additional sources
reviewed are cited in the discussion
below The BLM recognizes and targets
for treatment noxious weeds from the US
Department of Agriculture (USDA)
A noxious weed is any plant
designated as undesirable by a federal
state or county government as
injurious to public health agriculture
recreation wildlife or property
Noxious weeds are nonnative and
invasive Their control is based on
resource or treatment priorities and
is governed by budgetary constraints
Invasive plants include not only
noxious weeds but also other plants
that are not native to the United
States The BLM considers plants
invasive if they have been introduced
into an environment where they did
not evolve and as a result usually
have no natural enemies to limit their
reproduction and spread
(Westbrooks 1998)
3 Affected Environment and Environmental Consequences
3-48 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
Federal Noxious Weed List (USDA 2017) and the Nevada Department of
Agriculture (NDA)-maintained Nevada Noxious Weed List (NDA 2017) The
latter lists 47 noxious weed species in the state that require control
Numerous invasive nonnative and noxious weeds are present on the Ormat
project area described in the Salt Wells EIS (page 3-94 BLM 2011a) a portion
of which overlaps the Fallon FORGE project area These weeds are Russian
knapweed (Acroptilon repens) perennial pepperweed (Lepidium latifolium)
tamarisk (Tamarix spp) salt-lover (Halogeton glomeratus) and Russian olive
(Elaeagnus angustifolia) These species are commonly found along roads and near
other developed or disturbed areas
The most common noxious weeds and nonnative invasive plants on the NAS
Fallon main station (a portion of which overlaps the Fallon FORGE project area)
are Russian olive tamarisk Russian knapweed hoary cress (Cardaria draba)
curlycup gumweed (Grindelia squarrosa var serrulata) Russian thistle (Salsola
tragus) and cheatgrass (Bromus tectorum NAS Fallon 2014) Weeds on NAS
Fallon were mapped in 2008 and 2012 Weed control programs are ongoing
34000 acres of NAS Fallon were treated between 2009 and 2014
In 2017 Reclamation excavated an emergency canal to help drain Carson Lake
and alleviate flooding risk there are 2 miles of the canal in the project area
Currently side-cast soils from excavation provide ample substrate for noxious
weeds and nonnative invasive plants to colonize During a site visit in fall 2017
numerous weedy plant species including Russian thistle and salt-lover were
observed colonizing side-cast soils from excavation in the project area
3102 Environmental Consequences
An indicator of impacts from invasive nonnative and noxious weeds is the
potential for population establishment and spread as a result of the Proposed
Action The region of influence for direct and indirect impacts is the project area
Proposed Action
The nature and type of direct and indirect impacts from invasive nonnative and
noxious weeds (hereinafter referred to collectively as weeds) would be the
same as those described in Section 410 Invasive Nonnative Species of the Salt
Wells EIS (page 4-80 BLM 2011a) These include habitat degradation from weed
establishment and spread Potential impacts in the Fallon FORGE project area
that are outside of the scope of the Salt Wells EIS are described below
Under the Proposed Action drilling up to nine monitoring wells and three
productioninjection wells and installing new access roads and a site trailer
could disturb approximately 47 acres in the monitoring and productioninjection
wells assessment areas (FORGE GIS 2017) As described in Section 410 (page
4-81) of the Salt Wells EIS surface disturbance can facilitate weed establishment
and spread To minimize this impact applicable measures to prevent weed
establishment and spread from the approved weed management plan developed
3 Affected Environment and Environmental Consequences
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 3-49
for the Salt Wells projects would be incorporated into the Proposed Action
This would reduce or prevent weed establishment and spread from surface
disturbance during well pad and other project component construction
The potential for the Proposed Action to increase weed spread would be
minimized by preparing and implementing a noxious weed management plan
before construction begins as described in Appendix E Fallon FORGE
Environmental Protection Measures This would entail taking an accurate
baseline inventory of noxious weeds in the project area and tracking the
progress of weed treatments The plan would also outline best practices for
preventing weed establishment and spread such as using certified weed-free
materials and washing construction equipment before using it on-site A draft
plan outline is included as Appendix J of this EA Developing and implementing
this plan would reduce the potential for weed establishment and spread as a
result of the Proposed Action
Further applicable environmental protection measures and best management
practices as described in Appendix E of the Salt Wells EIS (BLM 2011a) would
apply to the Proposed Action These measures are included in Appendix C of
this EA These measures which include minimizing vegetation removal and
preventing noxious weed spread would reduce the potential for noxious weed
establishment and spread during all phases of development
As described above the emergency canal has created extensive areas of bare
side-cast soils in the project area which are becoming infested with weeds
These areas will continue to provide suitable substrate for weed establishment
unless they are proactively managed If weed populations become established
they will create large amounts of seeds and propagules7 increasing the potential
for weed establishment and spread in other portions of the project area This
impact would continue to occur regardless of preventive weed measures
incorporated into the Fallon FORGE project New weed populations originating
from this source may reduce the efficacy of adopted preventive measures
No Action Alternative
Under the No Action Alternative the BLM and Navy would not implement the
Proposed Action on federal lands None of the potential environmental impacts
associated with the Proposed Action would occur New weed propagation from
the emergency canal would continue
311 NATIVE AMERICAN RELIGIOUS CONCERNS
3111 Affected Environment
Native American resources are defined under various authorities including the
FLPMA the American Indian Religious Freedom Act Executive Order 13007
7 A bud sucker or spore
3 Affected Environment and Environmental Consequences
3-50 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
Native American Graves Protection and Repatriation Act and the National
Historic Preservation Act (NHPA) Under these authorities federal agencies
have the responsibility for managing Native American resources They pursue
this by in part taking such resources into consideration in land use planning and
environmental documentation and mitigating where possible impacts on places
or resources important to contemporary Native Americans and federally
recognized tribes
Slight differences in definitions among the authorities notwithstanding these
resources can be generally defined as places or resources such as plants and
animals associated with cultural practices or beliefs of a living community These
practices and beliefs are rooted in a tribal communityrsquos oral traditions or history
and are important in maintaining its continuing cultural identity In practice this
means identifying evaluating and managing ethnohistoric sites and resources
traditional use areas sacred and ceremonial sites and traditional cultural
properties
Since tribal heritage resources are defined culturally by the people and groups
who value them these resources can be identified and managed only in
consultation with the people who infuse them with cultural value In the final
analysis and decision-making a federal agency has the legal authority to
determine how these resources would be managed and what if any mitigation
would be used to avoid undue and unnecessary impacts on these resources
Ethnographic information indicates that Northern Paiute occupied the general
area including the project area and their way of life is characterized by the
concept of living in harmony with the natural environment Rituals and
ceremonies ensure that plants animals and physical elements flourish The
continued welfare of the people depends on these rituals and ceremonies being
performed properly and the resources being available The manner of
performing the rituals and ceremonies the places where they are performed
and perhaps even the time of their performance are often prescribed (BLM
2011a Salt Wells EIS)
Overall management of Native American resources are addressed by an
integrated cultural resource management plan (NAS Fallon 2013) For
withdrawn lands the Navy and the BLM have joint responsibility under a 2011
programmatic agreement between the Navy BLM and the Nevada State
Historic Preservation Office it defines how NAS Fallon and the BLM will
implement the NHPA Proposed BLM and Navy activities on withdrawn lands
are subject to NHPA Section 106 review which includes tribal consultation The
BLM consults with federally recognized tribes for all undertakings that may
affect historic properties places or resources important to contemporary
Native Americans in accordance with the Nevada Protocol Agreement (BLM
2014b)
3 Affected Environment and Environmental Consequences
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 3-51
3112 Environmental Consequences
Proposed Action
The BLM sent consultation notification letters to the Fallon Paiute-Shoshone
Tribal Council During consultation as part of the Salt Wells EIS the following
concerns were identified cultural resources including historic properties
continued access and use of the traditional sites and other resources that may
be affected No direct permanent impacts on access to or the use of traditional
use sites in the Salt Wells project area were identified and none are anticipated
as part of the Fallon FORGE Proposed Action Impacts on areas of Native
American religious concern often overlap with impacts on water quantity and
quality cultural resources visual resources and national and historic trails
Mitigation as part of the Salt Wells EIS required consultation and coordination
to maintain access to and use of any traditional sites To date no new locations
of Native American religious concerns have been identified If ongoing
consultation identifies locations or concerns these would be reviewed and as
appropriate and necessary additional monitoring and mitigation measures would
be developed Accordingly no impacts are anticipated
No Action Alternative
Under the No Action Alternative the BLM and Navy would not implement the
Proposed Action on federal lands None of the potential environmental impacts
associated with the Proposed Action would occur
312 LAND USE AIRSPACE AND ACCESS
3121 Affected Environment
Land Use
This section discusses the current landownership and use airspace
requirements and access in the proposed project area for the Fallon FORGE
site
The 1120-acre Fallon FORGE project area covers an area next to and including
a portion of the southeast section of the NAS Fallon main station The primary
uses in and near this area are agriculture the Newlands Project recreation
wildlife conservation naval air operations and ROWs for natural gas pipelines
transmission lines and communication facilities
As displayed in Figure 2 the Fallon FORGE project area and surrounding lands
consist of private lands and federal lands administered by the BLM US Navy
and Reclamation Land management and ownership acreages and percentages
are shown in Table 1-1 in Section 11 above
The federally administered lands near the proposed project area are the Carson
Lake and Pasture (administered by Reclamation) Stillwater National Wildlife
3 Affected Environment and Environmental Consequences
3-52 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
Refuge (administered by the USFWS) Grimes Point Archaeological Site
(administered by the BLM) the Fallon Paiute-Shoshone Indian Reservation
(administered by the US Bureau of Indian Affairs) and NAS Fallon (administered
by the DOD)
The Navy Integrated Natural Resources Management Plan (NAS Fallon 2014)
outlines how resources on Navy lands in the project vicinity are to be managed
The INRMP is a long-term planning document to guide the Navy in managing
natural resources while protecting and enhancing installation resources for
multiple use sustainable yield and biological integrity The primary purpose of
the INRMP is to maintain public access for wildlife viewing and other
recreational activities on lands not closed to the public for security or safety
The Navy promotes agricultural outleasing and other multiple land uses to the
maximum degree compatible with military operation requirements Parcels of
Navy-administered lands are opened for bid to local ranchers with the highest
bidder awarded a 5-year lease Use of the leased lands includes irrigation (on
water-righted acres) cattle grazing farming of alfalfa corn sudangrass and hay
and combinations of these uses (NAS Fallon 2014)
Reclamation-administered lands in the area are part of the Newlands Project
which TCID operates through a contract with Reclamation The Lahontan Basin
Area Office of Reclamation oversees the operation of the Newlands Project in
consultation with TCID the Pyramid Lake Paiute Tribe the USFWS the Fallon
Paiute-Shoshone Tribe and other regional stakeholders
Military Training and Airspace
NAS Fallon is the Navyrsquos primary air-to-air and air-to-ground training facility
Churchill County Code 1608240 contains provisions for land uses in the NAS
Fallon notification area which includes lands around the main station Section
1608240(J) requires notifying the NAS Fallon Commanding Officer of any new
redeveloped or rehabilitated buildings and structures This includes those used
for transmission communications or energy generation planned or proposed
within 3 miles of NAS Fallon boundary Structures with heights exceeding 75
feet will also require that NAS Fallon be notified to ensure navigable airspace
for military training (Churchill County 2017)
The project area is south of NAS Fallon main station which includes an airport
with control towers radar and runways industrial facilities for maintenance of
aircraft and support equipment business facilities for everyday operations retail
and recreation facilities housing for military personnel and their families and
utility support facilities such as for water and sewer (NAS Fallon 2014)
The runways and aprons comprising a flat paved asphalt area run in a northwest-
southeast orientation through the center of the station (see Figure 1) Land uses
next to each end of the runways are primarily agriculture and open space which
ensures compatibility with flight takeoff and landing operations
3 Affected Environment and Environmental Consequences
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 3-53
In the early 1970s the DoD established the AICUZ Program to balance the
need for aircraft operations with community concerns over aircraft noise and
accident potential The program goals are to protect the safety welfare and
health of those who live and work near military airfields while preserving the
military flying mission (NAS Fallon 2013) Through the AICUZ program the
Navy has modeled accident potential zones (APZs) at its air facilities APZs give
land use planners a tool to promote development that is compatible with airfield
operations
There are three APZ classifications (US Navy 2008)
1) The clear zone which has the greatest accident potential where no
structures except navigational aids and airfield lighting are allowed
2) APZ1 which is the area beyond the clear zone that still possesses a
measurable potential for accidents relative to the clear zone
3) APZ2 which has a measurable but lower potential for aircraft
accidents relative to clear zones and APZ1
Access
The project area can be accessed via US Highways 50 and 95 using Union Road
Pasture Road Berney Road Depp Road Shaffer Lane or Macari Lane There
are two segments of the Lincoln Highway (known as Berney Road in the north
and Macari Lane in the south) bisecting the project area The segments are
approximately 04 and 02 miles long
Beginning in April 2017 Reclamation authorized TCID to construct a new canal
in Churchill County for an emergency flood prevention project The
approximately 60-foot-wide and 16-mile-long emergency canal bisects the
project area in three areas for a total of 2 miles There are no culverts or
bridges where roads bisect the canal This prevents vehicle crossings and limits
access to portions of the proposed project area
3122 Environmental Consequences
Proposed Action
Indicators of impacts on land uses airspace and access include consistency with
federal state and local land uses compatibility with NAS Fallon and other
surrounding uses change in landownership and any change in the level of access
to or in the project area The region of influence for impacts on land use
airspace and access are all lands within the proposed project area boundary
Direct Impacts
Implementing the Proposed Action would not change any land uses or
landownership in the proposed project area
3 Affected Environment and Environmental Consequences
3-54 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
The Proposed Action would be consistent with the Churchill County 2015
Master Plan For example Goal CNR 4 identifies one of the Countyrsquos
conservation and natural resources goals Policy CNR 41 (Churchill County
2015) states ldquoEncourage and support development of renewable energy and
geothermal activity which provides benefit to Churchill County without
adversely impacting the surrounding community and environment including
migration routes nestingroosting sites unique habitats of wildlife and plant
species and monitor for no adverse impacts to wildlife and plant populationsrdquo
Impacts on wildlife from the Proposed Action would be expected to be minor
and localized and are further analyzed in Section 37
The Proposed Action would entail drilling up to three productioninjection wells
and up to nine monitoring wells These wells would allow for subsequent EGS
development and monitoring During construction drill rigs that are
approximately 120 feet tall would be used for drilling wells an activity that is
expected to last about 60 days per each of the nine monitoring wells and up to
120 days for the productioninjection wells This would have temporary impacts
on the APZs south of NAS Fallon
Nighttime lighting and transmitters on drill rigs would mitigate the potential for
interference with NAS Fallon operations After construction is completed the
permanent wellhead height would be less than 6 feet During well development
and operations the project proponent would coordinate closely with NAS
Fallon and the FAA to ensure compatibility with military aircraft operations and
to minimize the temporary impacts on accident potential zones
Direct access to the proposed project area would be via Highway 50 from
Berney Road or Macari Lane Impacts on access would occur if the historic
segments of the Lincoln Highway in the proposed project area were damaged
during construction and operation under the Proposed Action
Access to work locations in the project area would use to the extent possible
existing roads however an additional 21 miles of access roads may be
constructed to provide expanded access to proposed well pads
No indirect impacts on land use airspace or access have been identified in
relation to the Proposed Action
No Action Alternative
Under the No Action Alternative the BLM and Navy would not implement the
Proposed Action on federal lands None of the potential environmental impacts
associated with the Proposed Action would occur
313 FARMLANDS (PRIME OR UNIQUE)
The following data and information is presented to assist with agency
compliance with the Farmlands Protection Policy Act The locations and
3 Affected Environment and Environmental Consequences
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 3-55
acreages of prime and unique farmlands in the proposed project area are
identified based on information in the Natural Resources Conservation Service
(NRCS) online soils database (NRCS GIS 2017)
3131 Affected Environment
No land is classified as unique farmland in the proposed project area however
any potential prime farmland in the project area would require irrigation and
reclamation of salts and sodium There are 780 acres throughout the project
area that are considered potential prime farmland if reclaimed of salts (see
Table 3-7) Areas of non-prime farmland are generally in the northern portion
of the project area (see Figure 13 Farmland)
Table 3-7
Acres of Potential Prime Farmland
Not Prime
Farmland
Prime Farmland
if Irrigated
Prime Farmland If
Reclaimed of Salts
and Sodium
Total
Proposed project
area
300 40 780 1120
Source NRCS GIS 2017
3132 Environmental Consequences
Proposed Action
This section presents the consequences that the Proposed Action is likely to
have on Prime or Unique Farmlands Mitigation measures are discussed for
reducing any impacts that surface disturbance and constructed features may
have to agricultural operations
No land is classified as unique farmland in the proposed project area all
potential prime farmland would require irrigation and salt abatement
The consequences of the project on potential prime farmland include temporary
disruption of agricultural activities during construction of productioninjection
and monitoring wells and new access routes
The region of influence for direct and indirect impacts on prime or unique
farmlands includes areas where soil would be directly disturbed in the proposed
project area
In the potential prime farmland in the proposed project area 260 acres would
be in the monitoring and productioninjection well pad assessment areas There
could be up to 47 acres of disturbance in these areas however this amount of
disturbance would be unlikely given that not all wells and access roads would be
clustered in those portions of the assessment areas Disturbed areas would be
converted directly to non-farmland
3 Affected Environment and Environmental Consequences
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 3-57
The footprint of well pads and access roads would be the only locations where
occupancy would not allow agricultural use areas between well pads and access
roads could be available for farming The Proposed Action would be compatible
with agriculture uses and would not reduce opportunities to implement
agricultural practices on the remaining prime farmlands
No Action Alternative
Under the No Action Alternative the BLM and Navy would not implement the
Proposed Action on federal lands None of the potential environmental impacts
associated with the Proposed Action would occur
314 SOCIOECONOMICS
Demographic and economic data is generally provided at the county level
therefore the socioeconomic study area is defined as Churchill County
General descriptions of social and economic setting in the socioeconomic study
area are consistent with those described in the Salt Wells EIS (BLM 2011a)
Updated information relevant to the FORGE socioeconomic study area where
available is described below
3141 Affected Environment
Population in the socioeconomic study area is displayed in Table 3-8
Population estimates from 2012ndash2016 indicate that population has declined
slightly since 2010 in Churchill County and the city of Fallon
Table 3-8
Population in the Socioeconomic Study Area
Geography Population 2015 Population 2010 Population
Change
Churchill County 24148 24877 -29
City of Fallon 8410 8606 -23
Source US Census Bureau 2016 2010
Note 2016 data represent 2012ndash2016 American Community Survey 5-Year Estimates 2010 data are from the
2010 census
Annual unemployment levels in Churchill County for 2016 (54 percent) were
similar to those of the state (57 percent Headwater Economics 2017)
Current employment sectors in the socioeconomic study area are shown in
Table 3-9 Employment generated by the Proposed Action is likely to be in the
agriculture forestry fishing-hunting mining category Employment in this sector
currently represents 8 percent of employment This is much larger than the
state average due to the importance of farming and mining including
geothermal development Construction employment may also be generated by
the Proposed Action this sector has a similar level of employment as the county
and the state
3 Affected Environment and Environmental Consequences
3-58 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
Table 3-9
Employment by Industry in the Socioeconomic Study Area (2015)
Economic Sector
Churchill County Nevada
(Number of employees [percent employment]
for civilian employed population above age 16)
Agriculture forestry fishing-hunting and mining 739 (8) 21817 (17)
Construction 579 (62) 6664 (60)
Manufacturing 734 (79) 52723 (42)
Wholesale trade 135 (15) 26001 (21)
Retail trade 1057 (114) 151987 (120)
Transportation and warehousing 618 (67) 64333 (51)
Information 166 (18) 20940 (17)
Finance insurance and real estate 235 (25) 72784 (57)
Professional scientific management and administration 766 (83) 138342 (109)
Education health care and social assistance 1804 (195) 195743 (154)
Arts entertainment and recreation 872 (94) 328665 (259)
Other services 589 (64) 58360 (46)
Public administration 980 (106) 58935 (47)
TOTAL 9274 1267312
Source Headwater Economics 2017
3142 Environmental Consequences
Proposed Action
Under the Proposed Action construction and operation of up to three
productioninjection wells and nine monitoring wells may result in impacts on
local residents during the construction period from noise dust and traffic
Impacts would be short term and limited to the area immediately surrounding
the proposed disturbance areas
Specific to EGS potential impacts from induced seismicity would include the
threat of property damage and non-physical damage to humans such as sleep
disturbance (Majer et al 2007 Majer et al 2016) The potential for damage or
disturbance depends on the magnitude of a seismic event and the distance of the
property or human receptor from the source
Seismicity is influenced by the type of stimulation well depth geology and other
site specific factors (see Section 35 Geology for additional details) Literature
suggests that the potential to detect seismicity is generally limited to
approximately 74ndash93 miles of a drilling site and that impacts on structures are
limited to a narrower range (Majer et al 2016) For the project area a buffer of
5 miles was examined to determine the number of residences and other
structures with a potential for impact Based on aerial photos there are more
than 50 potential residences or other structures within the buffer area
Implementation of best practices to limit induced seismicity would reduce the
level of impacts on these residences (see Appendix B) Seismic monitoring
would be implemented before full-scale stimulation begins
3 Affected Environment and Environmental Consequences
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 3-59
The Fallon FORGE project represents the potential for additional employment
particularly in the construction sector Based on estimates in the Salt Wells EIS
well pads and associated wells typically require a crew of six workers for
construction The number of employees needed at a given time would depend
on the timing of development and the degree to which well drilling overlaps
Well depth and other factors influence costs and the number of employees
required EGS stimulation would also require additional costs and employment
for the length of the stimulation period
Some of the construction or operation jobs may be filled by workers already
residing in Churchill County some workers may come from outside the region
to fill new jobs or as contracted employees particularly for temporary
construction positions Employment data suggest that some qualified workers in
the sector may be available in the county accordingly the addition of these
temporary jobs would not increase the population employment or spending in
the county or strain public services
No Action Alternative
Under the No Action Alternative the BLM and Navy would not implement the
Proposed Action on federal lands None of the potential environmental impacts
associated with the Proposed Action would occur
3 Affected Environment and Environmental Consequences
3-60 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
This page intentionally left blank
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 4-1
CHAPTER 4
CUMULATIVE IMPACTS
Cumulative impacts are defined by the CEQ in 40 CFR Subpart 15087s as
ldquoimpacts on the environment which result from the incremental impact of the
action when added to other past present and reasonably foreseeable future
actions regardless of what agency (federal or non-federal) or person undertakes
such other actionsrdquo
Cumulative impacts can result from individually minor but collectively significant
actions taking place over time The analysis area for cumulative impact analysis is
stated for each resource
41 PAST PRESENT AND REASONABLY FORESEEABLE FUTURE ACTIONS
Past actions considered are those whose impacts on one or more of the
affected resources have persisted to today Present actions are those occurring
at the time of this evaluation and during implementation of the Proposed
Action Reasonably foreseeable future actions constitute those actions that are
known or could reasonably be anticipated to occur in the project area within a
time frame appropriate to the expected impacts from the Proposed Action
The primary past present and reasonably foreseeable future actions that would
contribute to cumulative impacts of the Proposed Action are military training
activities at NAS Fallon continued use of existing unpaved roads in the FORGE
project area continued exploration and development of geothermal resources
in leased areas continued use of land use authorizations the continued use of
the emergency canal and livestock grazing and ranching Table 4-1 identifies
known past present and reasonably foreseeable future actions in the FORGE
cumulative impacts assessment areas
4 Cumulative Impacts
4-2 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
Table 4-1
Past Present and Reasonably Foreseeable Future Actions
Action Location Description Completion
Date
Existing geothermal
exploration and
monitoring
Project area
and immediate
vicinity
There are numerous geothermal
exploration and monitoring wells in
and around the project area including
four deep wells in the project area
operated by Ormat
Ongoing
Salt Wells Geothermal
Project
Project area
and vicinity
Proposed 120-megawatt geothermal
power plant and transmission lines
Construction has
not begun
Enel Geothermal
Power Plant
18-megawatt geothermal power plant
approximately 8 miles southeast of the
project area
In operation
Newlands Project Churchill
Lyon Storey
and Washoe
Counties
Network of canals and irrigation
ditches that provide water to
agricultural lands in Lyon and Churchill
Counties
Operation and
maintenance is
ongoing
Emergency canal Project area
and immediate
vicinity
Emergency flood relief canal that was
constructed to relieve flooding in
Carson Lake
Spring 2017
Carson Lake and
Pasture land transfer
Churchill
County
In 1990 Congress passed Public Law
101-618 Section 206(e) of which
authorizes the Secretary of the Interior
to transfer title of the 22700 acres
comprising the Carson Lake and
Pasture area to the State of Nevada to
be managed by NDOW as a wildlife
management area The transfer is
pending completion
Transfer not
completed
Livestock grazing Project area
and vicinity
There is grazing on the privately
owned lands in the project area This
use is expected to continue
Ongoing
NAS Fallon military
training activities
Churchill
County
Military training at NAS Fallon will
continue on Navy lands next to the
project area
Ongoing
Grimes Point
Archaeological Area
Approximately
2 miles east of
the project
area
The Grimes Point Archaeological Area
and Petroglyph Trail managed by the
BLM provides visitors with a self-
guided interpretive trail experience
Year-round
visitation
Invasive nonnative
species and noxious
weeds
Project area Noxious weeds and nonnative species
continue to contribute to the
propagation of noxious weeds in the
project area
Ongoing
Churchill County
Master Plan
Churchill
County
The master plan establishes the
Countyrsquos vision for the future and
provides a decision-making framework
on matters relating to growth and
development throughout the county
2015
4 Cumulative Impacts
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 4-3
42 WATER RESOURCES
The cumulative impacts assessment area for surface water and groundwater is
the Fallon FORGE project area plus a 1-mile buffer
Combined with the other past present and reasonably foreseeable future
actions listed in Table 4-1 the Proposed Action would not result in
cumulatively significant impacts on water quality and quantity Water resources
in the region of influence would be affected by reasonably foreseeable future
actions such as canal construction (eg the Newlands Project and the
emergency canal) the Salt Wells Geothermal Project and existing geothermal
exploration and monitoring
These projects would have impacts on water resources similar to those
described for the Proposed Action For example the primary potential impacts
from surface water quality would be short term from any additional
construction completed at one or more of the well pads Impacts on surface
water could occur from increased erosion and sedimentation caused by ground
disturbance and removal of vegetation however mitigation using BMPs would
control these temporary impacts on surface water quality
Implementing stipulations applicable environmental protection measures and
best management practices outlined in Section 34 Water Resources would
minimize cumulative impacts on water resources Examples are imposing the
controlled surface use stipulation and complying with the stormwater pollution
prevention plan Additionally the environmental protection measures in
Appendix E of the Salt Wells EIS (included as Appendix C of this EA) would
help prevent contamination of surface water and groundwater from additional
drilling
The use of groundwater from adjacent geothermal wells could cumulatively
affect the quality and quantity of flows from the thermal spring (well 6) and
seeps due to pumping could reduce groundwater storage and could modify
deep groundwater flow paths and pressures These impacts would occur during
the period of deep groundwater pumping and for some time thereafter until the
affected deep groundwater system recovers to near equilibrium conditions
Any surface water impacts would require a permit from the US Army Corps of
Engineers all mitigation measures outlined in the permit would be strictly
adhered to further minimizing cumulative impacts Accordingly based on
potential impacts from past present and reasonably foreseeable future actions
in the assessment area no cumulatively significant impacts on water resources
are anticipated from implementing the Proposed Action
43 GEOLOGY
The cumulative impacts assessment area for geology is the same as that
identified under the environmental consequences for the Proposed Action
which is the project area
4 Cumulative Impacts
4-4 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
Geology in the region of influence would be affected by reasonably foreseeable
future actions such as canal construction (eg the Newlands Project and the
emergency canal) Salt Wells Geothermal Project and existing geothermal
exploration and monitoring These projects would have impacts on geology
similar to those described for the Proposed Action For example direct impacts
on surface geology would occur from the reasonably foreseeable future actions
This is because they likely would involve excavation which would disturb the
upper layers of the ground These impacts would likely last until the beginning of
any reclamation
Under the Proposed Action there would be direct and indirect impacts on
geology and seismicity The impacts would be negligible and minor
The Proposed Action when combined with the reasonably foreseeable future
actions identified in Table 4-1 could have cumulative impacts on geology and
seismicity These would occur by constructing infrastructure and inducing
microseismic events however it is not unreasonable to assume that continued
exploration and development of geothermal resources would be implemented
under practices similar to those of the Proposed Action that would minimize
impacts on geology Therefore the cumulative impacts on geology and
seismicity from the Proposed Action and the reasonably foreseeable future
actions would be minor
44 WETLANDS AND RIPARIAN AREAS
The cumulative impacts assessment area for wetlands and riparian areas is the
Fallon FORGE project area plus a 1-mile buffer
Past present and reasonably foreseeable future actions listed in Table 4-1 that
have affected and would continue to affect wetlands and riparian areas in the
assessment area are as follows existing and future exploration and development
of geothermal resources in leased areas military training activities at NAS
Fallon continued use of unpaved roads in the project area continued use of
land use authorizations and livestock grazing and ranching
There are numerous geothermal exploration and monitoring wells in and
around the project area including four deep wells in the project area operated
by Ormat The proposed 120-megawatt Salt Wells Geothermal Project would
also likely use geothermal resources in the analysis area Implementing the
Proposed Action in combination with these present and reasonably foreseeable
projects could cumulatively affect wetland and riparian areas Depending on the
hydraulic connection between the geothermal resources and surrounding
wetland areas saturation and flow volumes supporting wetland areas could be
altered by more geothermal wells Altered flow characteristics could in turn
alter wetland plant species composition total wetland area or surface or
subsurface water levels in wetlands
4 Cumulative Impacts
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 4-5
Combined with other past present and reasonably foreseeable future actions
the Proposed Action could also incrementally contribute to impacts on
wetlands and riparian areas from wetland and riparian area disturbance or
removal Disturbance or removal may come about during well pad or other
military livestock grazing or infrastructure construction or from increased
sedimentation or weed spread into the areas facilitated by these activities
Implementing stipulations and applicable environmental protection measures and
best management practices outlined in Section 36 Wetlands and Riparian
Areas would minimize cumulative impacts on wetlands and riparian areas
Specifically these stipulate no surface occupancy around wetland surface water
riparian and playa features complying with the stormwater pollution prevention
plan minimizing vegetation removal and preventing noxious weed spread
Conducting a wetland delineation on federal lease lands would ensure
compliance with the applicable lease stipulations relating to no surface
occupancy BLM approval of compliance would ensure impacts are minimized
Accordingly based on potential impacts from past present and reasonably
foreseeable future actions in the assessment area no cumulatively significant
impacts on wetlands and riparian areas are anticipated from implementing the
Proposed Action
If necessary disturbance or fill in wetlands may require a permit from the US
Army Corps of Engineers and all mitigation measures outlined in the permit
would be strictly adhered to further minimizing cumulative impacts
45 WILDLIFE AND KEY HABITAT
The cumulative impacts assessment area for wildlife and key habitat is the Fallon
FORGE project area plus a 1-mile buffer
Past present and reasonably foreseeable future actions listed in Table 4-1 that
have affected and would continue to affect wildlife and key habitat in the
assessment area are as follows
Military training at NAS Fallon
Continued use of unpaved roads in the project area
Continued exploration and development of geothermal resources in
leased areas
Continued use of existing land use authorizations
Construction and use of Newlands Project irrigation canals and
construction and use of the emergency canal
Livestock grazing and ranching
The Carson Lake and Pasture Land Transfer (pending) would transfer
management of the Carson Lake and Pasture to NDOW for wildlife habitat
4 Cumulative Impacts
4-6 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
This would have a beneficial cumulative impact by maintaining or increasing the
amount of high-quality habitat for general wildlife species in the assessment area
Combined with other past present and reasonably foreseeable future actions
the Proposed Action would incrementally contribute to impacts on wildlife and
key habitat The primary potential impacts would come from key habitat
disturbance or removal during well pad construction and from the potential
interference with wildlife disturbance injury mortality or movement
Implementing stipulations and applicable environmental protection measures and
best management practices outlined in Section 37 would minimize cumulative
impacts on wildlife and key habitat These are stipulating no surface occupancy
around wetlands and playa habitats imposing measures to prevent noxious
weed spread providing environmental education for workers preventing
overland travel avoiding sensitive habitats minimizing vegetation removal and
using measures to prevent wildlife entrapment or injury
Accordingly based on potential impacts from past present and reasonably
foreseeable future actions in the assessment area no cumulatively significant
impacts on wildlife and key habitat are anticipated from implementing the
Proposed Action
46 BLM SENSITIVE SPECIES
The cumulative impacts assessment area for BLM sensitive species is the project
area plus a 1-mile buffer
Past present and reasonably foreseeable future actions listed in Table 4-1 that
have affected and would continue to affect BLM sensitive species in the sensitive
species cumulative assessment area are as follows
Military training at NAS Fallon
Continued use of unpaved roads in the project area
Continued exploration and development of geothermal resources in
leased areas
Continued use of land use authorizations
Construction and use of Newlands Project irrigation canals and
construction and use of the emergency canal
Livestock grazing and ranching
The Carson Lake and Pasture Land Transfer (pending) would transfer
management of the Carson Lake and Pasture to NDOW for wildlife habitat
This would have a beneficial cumulative impact by maintaining or increasing the
amount of high-quality habitat for BLM-sensitive species in the assessment area
4 Cumulative Impacts
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 4-7
Combined with other past present and reasonably foreseeable future actions
the Proposed Action would incrementally contribute to impacts on BLM
sensitive plants and wildlife The primary impacts would be the potential for
foraging habitat loss for raptors and bat species from habitat loss during well
pad construction and the potential for disturbance during construction The
Proposed Action could also reduce the amount of suitable habitat for BLM-
sensitive plants either through habitat disturbance or weed establishment and
spread
Implementing stipulations and applicable environmental protection measures and
best management practices outlined in Section 38 BLM Sensitive Species
would minimize cumulative impacts on these species These measures are as
follows adhering to applicable measures in the approved avian protection plan
for the Salt Wells projects imposing the no surface occupancy stipulation
around wetlands and playa habitats implementing measures to prevent noxious
weed spread providing environmental education for workers preventing
overland travel avoiding sensitive habitats minimizing vegetation removal and
using measures to prevent wildlife entrapment or injury
Accordingly based on potential impacts from past present and reasonably
foreseeable future actions in the assessment area no cumulatively significant
impacts on BLM sensitive species are anticipated from implementing the
Proposed Action
47 MIGRATORY BIRDS
The cumulative impacts assessment area for migratory birds is the project area
plus a 1-mile buffer
Past present and reasonably foreseeable future actions that have affected and
would continue to affect migratory birds in the cumulative assessment area are
as follows
Military training at NAS Fallon and the NAS Fallon BASH program
Continued exploration and development of geothermal resources in
leased areas
Construction of the Salt Wells Geothermal projects and
construction and use of Newlands Project irrigation canals
Construction and use of the emergency canal
The Carson Lake and Pasture Land Transfer (pending) would transfer
management of the Carson Lake and Pasture to NDOW for wildlife habitat
This would have a beneficial cumulative impact by maintaining or increasing the
amount of high-quality habitat for numerous species of migratory birds including
waterfowl in the assessment area
4 Cumulative Impacts
4-8 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
Combined with other past present and reasonably foreseeable future actions
the Proposed Action would incrementally contribute to impacts on migratory
birds The primary impacts would be the potential for habitat loss and
disturbance or displacement from habitat during construction Disturbance
during the nesting season could result in songbird or waterfowl nest
abandonment however conducting surveys for and avoiding nests would
eliminate the potential for this
Further applicable environmental protection measures and best management
practices would reduce or avoid impacts on migratory birds and their habitat
This would come about by providing environmental education for workers
preventing overland travel minimizing vegetation removal and implementing
measures to prevent wildlife entrapment or injury
Accordingly based on potential impacts from past present and reasonably
foreseeable future actions in the assessment area no cumulatively significant
impacts on migratory birds are anticipated from implementing the Proposed
Action
48 INVASIVE NONNATIVE AND NOXIOUS SPECIES WEED
The cumulative impacts assessment area for weeds is the Fallon FORGE project
area plus a 1-mile buffer
Past present and reasonably foreseeable future actions listed in Table 4-1 that
have affected and would continue to affect weeds in the cumulative impacts
assessment area are as follows
Military training activities at NAS Fallon
Continued use of unpaved roads in the project area
Continued exploration and development of geothermal resources in
leased areas
Continued use of land use authorizations
Construction and use of Newlands Project irrigation canals and
construction and use of the emergency canal
Livestock grazing and ranching
Combined with other past present and reasonably foreseeable future actions
the Proposed Action would incrementally contribute to impacts on weeds The
primary potential impact would be the potential for weed establishment and
spread during construction resulting in surface disturbance and vegetation
removal Side-cast soils along the emergency canal would continue to provide
suitable substrate for weed establishment and propagation throughout the
project area
4 Cumulative Impacts
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 4-9
Implementing stipulations and applicable environmental protection measures and
best management practices outlined in Section 310 Invasive Nonnative and
Noxious Weed Species would minimize cumulative impacts Even so weeds
would continue to become established due to canal disturbance regardless of
preventive weed measures incorporated into the Fallon FORGE project New
weed populations originating from this source may reduce the efficacy of
adopted preventive measures such as those from the approved Salt Wells
projects
49 NATIVE AMERICAN RELIGIOUS CONCERNS
The cumulative impacts study area for Native American religious concerns in
the project area and surrounding lands that tribes and individual Native
Americans value for religious or traditional cultural purposes In this area
cumulative impacts have occurred on lands that have provided and continue to
provide sustenance and spiritual and religious renewal for the indigenous
people Mineral development water conveyance systems cattle grazing and
other actions cumulatively have affected or would affect these resources and
Fallon Paiute-Shoshone tribal tradition and lifeways
No additional impacts are anticipated from the Proposed Action therefore no
change in the nature type or extent of cumulative impacts is anticipated when
combined with reasonably foreseeable future actions
410 LAND USE AIRSPACE AND ACCESS
The cumulative impacts assessment area for land use airspace and access is the
same as that identified under impacts for the Proposed Action
Past present and reasonably foreseeable future actions listed in Table 4-1 that
have affected and would continue to affect land use airspace and access in the
cumulative impacts assessment area are military training activities at NAS Fallon
(including within accident potential zones) continued use of existing and newly
created unpaved roads in the project area continued exploration and
development of geothermal resources continued use of existing land use
authorizations use of the emergency canal and livestock grazing and ranching
Combined with other past present and reasonably foreseeable future actions
the Proposed Action would incrementally contribute to impacts on land use
airspace and access The primary potential impact would be from conflicts with
nearby land uses from the increase or modification of access in the region of
influence or from the conflict with airspace safety zones designated by the
Navy however any future projects would require approval from the land
management agency with jurisdiction over the project lands The projects would
be developed to be consistent with federal state and local land use plans and
policies therefore potential cumulative impacts on land uses airspace or access
would be minimized
4 Cumulative Impacts
4-10 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
There would be ongoing cumulative impacts on access through the project area
from the emergency canal Until new road crossings are constructed or it is
filled in the canal would prevent through-travel on any access road that the
canal bisects Where the canal prevents access there may be a cumulative
impact on access in the project area unless new roads can compensate for the
loss of access
Accordingly based on potential impacts from past present and reasonably
foreseeable future actions in the assessment area no cumulatively significant
impacts on land use airspace and access are anticipated from implementing the
Proposed Action
411 FARMLANDS (PRIME OR UNIQUE)
The region of influence for cumulative impacts on farmlands includes areas
where soil would be directly disturbed in the Proposed Action area
The largest threat to potential Prime Farmlands near Fallon is the removal of
water rights Changes in upstream water rights and the purchases of water
rights in the area could change the number of water rights available NAS Fallon
has instituted a program to purchase and conserve adjacent lands in agricultural
uses and Churchill County has an easement purchasing program to promote
farmland conservation Residential development pressure has occurred but has
been partially offset by the previously described conservation programs (BLM
2011a)
Due to the deficiency in precipitation (approximately 5 inches per year
[Western Regional Climate Center 2016]) compared to evapotranspiration
(over 60 inches per year [Western Regional Climate Center 1992]) irrigation is
necessary for productive farming near Fallon however the Proposed Action
would not divert irrigation water from agricultural application Water needed
for the EGS testing operations would be supplied from groundwater sources
The Proposed Action when combined with the reasonably foreseeable future
actions identified in Table 4-1 could have cumulative impacts on potential
Prime Farmlands This would result from implementing activities or construction
that would preclude lands from being used for agricultural purposes such as
construction of the Salt Wells Geothermal Project
Also projects that increase surface water availability for irrigation such as
construction of additional canals in the Newlands Project could affect potential
Prime Farmlands Cumulative impacts on potential Prime Farmlands from the
Proposed Action and the reasonably foreseeable future actions are expected to
be minor
4 Cumulative Impacts
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 4-11
412 SOCIOECONOMICS
The region of influence for cumulative impacts on socioeconomics is the same
as that identified under the impacts for the Proposed Action which is Churchill
County
Past present and reasonably foreseeable future actions that have affected and
would continue to affect socioeconomics are regional employment and potential
seismicity from EGS Proposed actions including future geothermal
development (see Table 4-1) represent additional regional employment needs
The level of demand for employment would depend on the degree of overlap
with the Proposed Action Although the Proposed Action presents the potential
for additional employment particularly in the construction sector the jobs
would be either temporary or would only nominally increase the permanent
population employment or spending in the region The Proposed Action would
not strain public services therefore contributions to cumulative impacts on
socioeconomics would be minimal
The potential for damage or disturbance from induced seismicity depends on
the distance from the source and the magnitude of the seismic event
Implementing best practices to limit induced seismicity would reduce the level
of cumulative impacts (see Section 35 Geology for additional discussion of
induced seismicity)
413 NO ACTION ALTERNATIVE
Under the No Action Alternative there would be no additional wells drilled to
support geothermal research There would be no impacts on any of the
identified resources or activities
414 SUMMARY OF CUMULATIVE IMPACTS
All resource values have been evaluated for cumulative impacts Cumulative
impacts from implementing the Proposed Action or No Action Alternative have
been determined to be negligible
415 IRREVERSIBLE AND IRRETRIEVABLE COMMITMENT OF RESOURCES
The irreversible commitment of resources is described as the ldquoloss of future
optionsrdquo It applies primarily to nonrenewable resources such as cultural
resources or resources that are renewable after a regeneration period such as
soil productivity The term may also apply to the loss of an experience as an
indirect impact of a permanent change in the nature or character of the land
An irretrievable commitment of resources is defined as the loss of production
harvest or use of natural resources The amount of production foregone is
irretrievable but the action is not irreversible No irreversible and irretrievable
commitment of resources is expected as a result of the Proposed Action
4 Cumulative Impacts
4-12 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
416 RELATIONSHIP BETWEEN LOCAL SHORT-TERM USE OF THE HUMAN ENVIRONMENT AND MAINTENANCE AND ENHANCEMENT OF LONG-TERM NATURAL RESOURCE PRODUCTIVITY
Development and construction proposed to occur from implementing the Proposed Action is not expected to result in the types of impacts that would reduce environmental productivity have long-term impacts on natural resources or resource uses affect biodiversity or narrow the range of long-term beneficial uses of the environment As discussed in Chapter 3 the Proposed Action would not result in short- and long-term significant environmental effects
Short-term uses of the environment associated with the Proposed Action would include constructing well pads and drilling productioninjection and monitoring wells to support EGS activities Project-related construction activities would result in localized temporary impacts such as noise from vehicles and well drilling Noise from construction activities would be short-term and would not be expected to result in permanent damage or long-term changes in wildlife productivity or habitat use
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 5-1
CHAPTER 5
CONSULTATION AND COORDINATION
51 AGENCIES GROUPS AND INDIVIDUALS CONTACTED
The following agencies groups and individuals were contacted for the
preparation of the Fallon FORGE Geothermal Research Project EA
Native American Consultation
Fallon Paiute-Shoshone Tribal Council
Federal Agencies
US Fish and Wildlife Service
US Department of Energy
State Agencies
Nevada Department of Wildlife
Nevada Natural Heritage Program
Cooperating Agencies
US Navy
US Bureau of Reclamation
Other Entities
Ormat Nevada Inc
Sandia National Laboratories
5 Consultation and Coordination
5-2 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
52 LIST OF PREPARERS
Table 5-1
List of Preparers
Name Project Expertise
BLM Carson City District Stillwater Field Office
Dave Schroeder Project Lead geothermal resources wastes hazardous or solid
Kenneth Collum Stillwater Field Office Manager
Carla James Stillwater Assistant Field Manager
Linda Appel Vegetation wild horses and burros
Keith Barker Fire management vegetation
Melanie Cota Migratory birds threatened or endangered species special status
species (BLM Sensitive Species) general wildlife
Kenneth Depaoli Geologist
Jason Grasso Realty Specialist
Melanie Hornsby Recreation ACEC travel management wildernessWSA lands with
wilderness characteristics environmental justice NEPA compliance
Mark Mazza Rangeland noxious and invasive nonnative species
Michelle Stropky Hydrology air quality farm lands (Prime and Unique) floodplains
surface water and groundwater quality soils
Jason Wright Cultural resources Native American religious concerns visual
resources paleontology
US Department of the Navy
Nathan Accoraci US Navy NAS Fallon
Mike Klapec US Navy NAS Fallon
Andrew Tiedeman US Navy Geothermal Program Office
Environmental Management and Planning Solutions Inc
Peter Gower Project Manager
Jacob Accola Geographic information systems
Sean Cottle Land use airspace and access administrative record
Kevin Doyle Native American and religious concerns
Zoe Ghali Socioeconomics
Derek Holmgren Geology
Jenna Jonker Geographic information systems
Laura Patten Water resources
Cindy Schad Word processing
Jennifer Thies NEPA Specialist
Morgan Trieger Wildlife and key habitat BLM sensitive species invasive nonnative and
noxious weed species wetlands and riparian areas migratory birds
Randolph Varney Technical editing
Meredith Zaccherio Quality assurancequality control
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 6-1
CHAPTER 6
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Consolidated Resource Management Plan Carson City Nevada
_____ 2007 Surface Operating Standards and Guidelines for Oil and Gas Exploration and
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_and_gasPar18714FiledatOILgaspdf
_____ 2008a Carson Lake Geothermal Exploration Project Environmental Assessment (EA-NV-030-
07-006) July 2008 Carson City Nevada
_____ 2008b BLM National Environmental Policy Act Handbook H-1790-1 January 2008 Washington
DC
_____ 2008c Final Programmatic Environmental Impact Statement for Geothermal Leasing in the
Western United States FES 08-44 Internet website wwwblmgovwostenprog
energygeothermalgeothermal_nationwideDocumentsFinal_PEIShtml
_____ 2011a Final Environmental Impact Statement Salt Wells Energy Projects Carson City District
Stillwater Field Office July 2011 Carson City Nevada
_____ 2011b Newberry Volcano Enhanced Geothermal System (EGS) Demonstration Project
Environmental Assessment DOI-BLM-OR-P000-2011-0003-EA Prineville Oregon
_____ 2013 Environmental Assessment DOI-BLM-NV-W010-2012-0057-EA DOEEA-1944 Brady
Hot Springs Well 15-12 Hydro-Stimulation Winnemucca Nevada January 2013
_____ 2014a Draft Resource Management Plan and Environmental Impact Statement Carson City
District November 2014 Carson City Nevada
6 References
6-2 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
_____ 2014b State Protocol Agreement between the Bureau of Land Management Nevada and the
Nevada State Historic Preservation Office as amended December 2014 Carson City Nevada
_____ 2015 Nevada and Northeastern California Greater Sage-Grouse Approved Resource
Management Plan Amendment Bureau of Land Management Nevada State Office Reno
Nevada
BLM and Forest Service (US Department of Agriculture Forest Service) 2007 Surface Operating
Standards and Guidelines for Oil and Gas Exploration and Development (Gold Book) Fourth
Ed Washington DC
BLM GIS 2017 GIS data of BLM NVCA ARMPA GRSG Habitat updated 6302017 Internet website
httpsnavigatorblmgovdatakeyword=GRSGampfs_publicRegion=Nevada
Bradley P V M J OrsquoFarrell J A Williams and J E Newmark (editors) 2006 The Revised Nevada Bat
Conservation Plan Nevada Bat Working Group Reno Nevada
Butterflies of America 2018 Pseudocopaeodes eunus flavus Austin amp J Emmel 1998 (Alkali Skipper)
Internet website httpwwwbutterfliesofamericacompseudocopaeodes_eunus_flavushtm
CEQ (Council on Environmental Quality) 1997 Considering Cumulative Effects Under the National
Environmental Policy Act Internet website httpsenergygovsitesprodfilesnepapubnepa_
documentsRedDontG-CEQ-ConsidCumulEffectspdf
Churchill County 2015 Churchill County Master Plan Internet website httpwwwchurchill
countyorgDocumentCenterView8884
_____ 2017 Nevada County Code Internet website httpwwwsterlingcodifierscom
codebookindexphpbook_id=351
Chisholm G and L A Neel 2002 Birds of the Lahontan Valley A Guide to Nevadarsquos Wetland Oasis
University of Nevada Press Reno
Cowardin L M V Carter F C Golet and E T LaRoe 1979 Classification of Wetlands and
Deepwater Habitats of the United States US Department of the Interior US Fish and Wildlife
Service FWSOBS-7931 Washington DC
DOD (US Department of Defense) 1996 Department of Defense Instruction Number 471503
Internet website httpwwwdodnaturalresourcesnetfilesDoDI_4715_03pdf
DOI (US Department of the Interior) 2009 Department of the Interior Departmental Manual 516
Washington DC
EPA (Environmental Protection Agency) GIS 2015 GIS data of 303(d) listed impaired waters Internet
website httpswwwepagovwaterdatawaters-geospatial-data-downloads
FEMA (Federal Emergency Management Agency) GIS 2017 GIS data of flood zones Internet website
httpsgdgscegovusdagovGDGOrderaspx
6 References
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 6-3
Floyd T C Elphick G Chisholm K Mack R Elston E Ammon and J Boon 2007 Atlas of the Breeding
Birds of Nevada University of Nevada Press Reno
FORGE GIS 2017 Base and project data from the DOE FORGE program Data received through
various means
Headwater Economics 2017 Economic Profile System Internet website httpsheadwaters
economicsorgtoolseconomic-profile-systemabout
Hinz N H J E Faulds D L Siler B Tobin K Blake A Tiedeman A Sabin D Blankenship M
Kennedy G Rhodes J Nordquist S Hickman J Glen C Williams A Robertson-Tait W
Calvin 2016 Stratiagraphic and Structural Framework of the Proposed Fallon FORGE Site
Nevada Standford University Stanford CA
Ivey G L and C P Herziger 2006 Intermountain West Waterbird Conservation Plan Version 12 A
plan associated with the Waterbird Conservation for the Americas Initiative Published by US
Fish and Wildlife Service Pacific Region Portland Oregon
Majer E L R Baria M Stark S Oates J Bommer B Smith and H Asanuma 2007 ldquoInduced seismicity
associated with Enhanced Geothermal Systemsrdquo Geothermics 36 (2007) 185ndash222
Majer E L J Nelson A Robertson-Tait J Savy and I Wong 2012 Protocol for Addressing Induced
Seismicity Associated with Enhanced Geothermal Systems DOEEE-0662 January 2012
Washington DC
_____ 2016 Best Practices for Addressing Induced Seismicity Associated with Enhanced Geothermal
Systems (EGS) April 8 2016 Washington DC
Michigan Technological University 2017 How Are Earthquake Magnitudes Measured Internet website
httpwwwgeomtueduUPSeisintensityhtml
Morefield J D 2001 Nevada Rare Plant Atlas Internet website httpheritagenvgovatlas
NAS Fallon (Naval Air Station Fallon) 1990 Programmatic Environmental Impact Statement
Geothermal Energy Development Naval Air Station Fallon Fallon Nevada February 1990
_____ 2012 Final Integrated Cultural Resources Management Plan Naval Air Station Fallon Nevada
Volumes I and II
_____ 2013 Final Environmental Assessment for Airfield Operations at Naval Air Station Fallon
Nevada August 2013
NAS Fallon and State of Nevada 2011 Programmatic Agreement among Naval Air Station Fallon the
Nevada State Historic Preservation Officer and the Advisory Council on Historic Preservation
Regarding the Identification Evaluation and Treatment of Historic Properties on Lands Managed
by Naval Air Station Fallon July 2011
6 References
6-4 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
_____ 2014 Final Integrated Natural Resources Management Plan Naval Air Station Fallon Fallon
Nevada Naval Facilities Engineering Command Southwest Report Contract N62473-07-D-
32010011 San Diego California NASF GIS 2017 GIS data on file with Naval Air Station Fallon
Nevada
NatureServe 2017 NatureServe Explorer An online encyclopedia of life [web application] Version 71
NatureServe Arlington Virginia Internet website httpexplorernatureserveorg
Navy (US Department of the Navy) 2008 OPNAVINST 1101036C Air Installations Compatible Use
Zones Program October 9 2008 Fallon Nevada
_____ 2006 Secretary of the Navy Instruction 50908A Internet website httpwwwsecnavnavymil
eieASN20EIE20PolicySECNAVINST_50908Apdf
_____ 2014 OPNAV Manual M-50901D Environmental Readiness Program Manual Internet website
httpwwwnavseanavymilPortals103DocumentsSUPSALVEnvironmentalOPNAVINST205
090-1Dpdf
_____ 2012 Strategy for Renewable Energy Internet website httpwwwsecnavnavymileie
ASN20EIE20PolicyDASN_EnergyStratPlan_Finalv3pdf
NDA (Nevada Department of Agriculture) 2017 Nevada Noxious Weed List Internet website
httpagrinvgovPlantNoxious_WeedsNoxious_Weed_List
NDEP (Nevada Division of Environmental Protection) 2014 Nevada 2012 Water Quality Integrated
Report With EPA Overlisting Internet website httpsndepnvgovuploads
documentsIR2012_Report_Finalpdf
NDOW (Nevada Department of Wildlife) 2017 Letter from Bonnie Weller NDOW to Morgan
Trieger EMPSi Re Fallon FORGE Project November 13 2017 NDOW Reno Nevada
_____ No date Design Features and Tools to Reduce Wildlife Mortalities Associated with Geothermal
Sumps NDOW Reno Nevada
Nevada Bureau of Mines and Geology 2017 Quaternary Faults in Nevada Internet website
httpsgiswebunreduQuaternaryFaults Accessed on November 20 2017
Nevada Division of Water Resources 2018 Permit Information Internet website
httpwaternvgovPermitSearchaspx
NHD (National Hydrography Dataset) GIS 2017 National Hydrography Dataset high resolution
geospatial dataset Internet website httpsnhdusgsgovNHD_High_Resolutionhtml
NNHP (Nevada Natural Heritage Program) 2017 Re Data RequestmdashFORGE Geothermal EA NNHP
Reno Nevada
6 References
March 2018 FORGE Geothermal Research and Monitoring Environmental Assessment 6-5
NRCS (Natural Resources Conservation Service) GIS 2017 GIS data of soils and soil attributes from
the Web Soil Survey United States Department of Agriculture Internet website
httpswebsoilsurveyscegovusdagovAppWebSoilSurveyaspx
Reclamation (US Bureau of Reclamation) 2014 Newlands Project Resource Management Plan and Final
Environmental Impact Statement November 18 2014 Internet website httpswwwusbrgov
mpnepanepa_project_detailsphpProject_ID=2822
Reclamation GIS 2017 GIS data of emergency canal approximate location and existing canal network
SNL (Sandia National Laboratories) 2016 Frontier Observatory for Research in Geothermal Energy
Phase 1 Topical Report (Sandia Report SAND2016-8929) Internet website httpsenergygov
sitesprodfiles201609f33Fallon20Topical20Report_20168929_Sept2016_1pdf
_____ 2018 Fallon FORGE Geothermal Well Data
Truckee-Carson Irrigation District 2010 Newlands Project Water Conservation Plan Internet website
httpwwwtcidorgpdfwcp10fpdf
US Census Bureau 2015 American Community Survey 2012-2015 5 year data Internet website
httpsfactfindercensusgovfacesnavjsfpagessearchresultsxhtmlrefresh=t
USDA (US Department of Agriculture Natural Resources Conservation Service) 2017 Introduced
Invasive and Noxious PlantsmdashFederal Noxious Weeds Internet website httpsplantsusda
govjavanoxious
USDOE 2017 EGS About Fallon FORGE Internet website httpesd1lblgovresearchprojects
induced_seismicityegsfallonforgehtml
USFWS (US Department of the Interior Fish and Wildlife Service) 2017 Official Species List Fallon
Frontier Observatory for Geothermal Research (FORGE) Geothermal Research and
Monitoring Consultation Code 08ENVD00-2018-SLI-0085 November 10 2017 USFWS Reno
Nevada
USFWS GIS 2017a National Wetland Inventory GIS data of wetlands Internet website
httpswwwfwsgovwetlandsdatadata-downloadhtml
_____ 2017b GIS data of mapped critical habitat Internet website httpsecosfwsgovecp
reporttablecritical-habitathtml
USGS (US Department of the Interior US Geological Survey) 2017 Geologic Provinces of the United
States Basin and Range Province Internet website httpsgeomapswrusgsgovparks
provincebasinrangehtml
_____ 2016 Groundwater Quality in the Basin and Range Basin-Fill Aquifers Southwestern United
States Internet website httpspubsusgsgovfs20163080fs20163080pdf
6 References
6-6 FORGE Geothermal Research and Monitoring Environmental Assessment March 2018
USGS SWReGAP GIS 2004 Provisional Digital Land Cover Map for the Southwestern United States
Version 10 RSGIS Laboratory College of Natural Resources Utah State University
Westbrooks R 1998 Invasive Plants Changing the Landscape of America Fact Book Federal
Interagency Committee for the Management of Noxious and Exotic Weeds Washington DC
Wildlife Action Plan Team 2012 Nevada Wildlife Action Plan Nevada Department of Wildlife Reno
Internet website httpwwwndoworgNevada_WildlifeConservationNevada_Wildlife_Action
_Plan
Western Regional Climate Center 1992 Evaporation Stations Nevada Monthly Average Pan
Evaporation Internet website httpswrccdrieduhtmlfileswestevapfinalhtmlNEVADA
_____ 2016 Climate Summary Fallon EXP STN Nevada (262780) Period of Record June 1 1903 to
April 30 2016 Internet website httpswrccdrieducgi-bincliMAINplnv2780
Appendix A EGS Protocol
This page intentionally left blank
GEOTHERMAL TECHNOLOGIES PROGRAM
Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
by
Ernie Majer James Nelson Ann Robertson-Tait Jean Savy and Ivan Wong
January 2012 | DOEEE-0662
Cover Image
Courtesy of Katie L Boyle Lawrence Berkeley National Laboratory
i
i Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Preface
In June 2009 the New York Times published an article about the public fear of geothermal development causing earthquakes The article highlighted a project funded by the US Department of Energyrsquos (DOE) Geothermal Technologies Program bringing power production at The Geysers back up to capacity using Enhanced Geothermal Systems (EGS) technology The Geysers geothermal field is located two hours north of San Francisco California and therefore the article drew comparisons to a similar geothermal EGS project in Basel Switzerland believed to cause a magnitude 34 earthquake
In order to address public concern and gain acceptance from the general public and policymakers for geothermal energy development specifically EGS the US Department of Energy commissioned a group of experts in induced seismicity geothermal power development and risk assessment to write a revised Induced Seismicity Protocol The authors met with the domestic and international scientific community policymakers and other stakeholders to gain their perspectives and incorporate them into the Protocol They also incorporated the lessons learned from Basel Switzerland and other EGS projects around the world to better understand the issues associated with induced seismicity in EGS projects The Protocol concludes that with proper study and technology development induced seismicity will not only be mitigated but will become a useful tool for reservoir management
This Protocol is a living guidance document for geothermal developers public officials regulators and the general public that provides a set of general guidelines detailing useful steps to evaluate and manage the effects of induced seismicity related to EGS projects This Protocol puts high importance on safety while allowing geothermal technology to move forward in a cost effective manner
The goal of this Protocol is to help facilitate the successful deployment of EGS projects thus increasing the availability of clean renewable and domestic energy in the United States
Project developers should work closely with the National Environmental Policy Act (NEPA) compliance officials of the involved Federal agency(ies) to align information needs and public involvement activities with the NEPA review process The authors emphasize this Protocol is neither a substitute nor a panacea for regulatory requirements that may be imposed by federal state or local regulators
I would like to acknowledge everyone who gave their time and expertise at the induced seismicity workshops (see Appendix D) that led to this updated Protocol Their input was critical to develop an informed and useful document In addition I would like to thank the authors of this document whose ideas and support came together to write a clear and concise Protocol
This document was put out for public comment and reviewed by NEPA the US Department of Energy and General Counsel Special thanks to Christy King-Gilmore and Brian Costner for their guidance
Sincerely
Jay Nathwani
US Department of Energy
ii Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
iii
iii Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Table of Contents1 Introduction 1
11 Intended Use 1
12 Objective 2
13 Background 2
2 Steps in Addressing Induced Seismicity 5
STEP 1 Perform Preliminary Screening Evaluation 6 211 Purpose 6
212 Recommended Approach 6
213 Summary 7
STEP 2 Implement an Outreach and Communication Program 8 221 Purpose 8
222 Recommended Approach 8
223 Summary 10
STEP 3 Review and Select Criteria for Ground Vibration and Noise 11 231 Purpose 11
232 Recommended Approach 11
233 Summary 12
STEP 4 Establish Local Seismic Monitoring 13 241 Purpose 13
242 Recommended Approach 13
243 Summary 14
STEP 5 Quantify the Hazard from Natural and Induced Seismic Events 15 251 Purpose 15
252 Recommended Approach 16
253 Summary 17
STEP 6 Characterize the Risk of Induced Seismic Events 18 261 Purpose 18
262 Recommended Approach 18
263 Summary 20
STEP 7 Develop Risk-Based Mitigation Plan 21 271 Purpose 21
272 Recommended Approach 21
273 Summary 23
3 Acknowledgements 25
4 References 27
Appendices A Background amp Motivation Induced Seismicity Associated with Geothermal Systems 29
B List of Acronyms 39
C Glossary of Terms 41
D Workshop ParticipantsReviewers 43
E Relevant Websites 45
iv Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
1
1 INTRODUCTION
1 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
1 Introduction
Geothermal energy is a viable form of alternative energy that is expected to grow significantly in the near and long term The energy estimated from hydrothermal systems is large but the total supply from geothermal systems has the potential to become orders of magnitude larger if the energy from geothermal systems can be enhanced ie through Enhanced Geothermal Systems (EGS) EGS is defined as any activities that are undertaken to increase the permeability in a targeted subsurface volume via injecting and withdrawing fluids into and from the rock formations that are intended to result in an increased ability to extract energy from a subsurface heat source This can be done through such approaches as fluid pressurization hydrofracture and chemical stimulation As with the development of any new technology some aspects are accepted and others need clarification and study In the case of EGS fluid injection is used to enhance rock permeability and recover heat from the rock During the process of creating an underground heat exchanger by injection or the subsequent circulation of the system stress patterns in the rock may change resulting in seismic events (see Appendix A Background and Motivation) In almost all cases these events have been of relatively small magnitude and by the time the energy reaches the surface the vast majority are rarely felt (Majer et al 2007) The impacts of a seismic event created by EGS can be significantly different from those associated with a natural earthquake the former generally falls into the category of an annoyance as with the passing of a rail transit vehicle or large truck whereas the latter may cause damage in a moderate to large event Although to date there is no recorded instance of a significant danger or damage (significant is defined here as damage that would affect a structurersquos physical integrity this is not to say that seismicity has not caused less severe damage such as cracks in walls or similar damage) associated with induced seismicity related to geothermal energy production the introduction of EGS technology in populated areas could be regarded by some as an intrusion on the peace and tranquility of populated areas due to its potential ldquoannoyance factorrdquo
Historically induced seismicity has occurred in many different energy and industrial applications (reservoir impoundment mining construction waste disposal and oil and gas production) Although certain projects have stopped because of induced seismicity issues proper study and engineering controls have always been applied to enable the safe and economic implementation of these technologies Recent publicity surrounding induced seismicity at several geothermal sites points out the need to address and mitigate any potential problems that induced seismicity may cause in geothermal projects (Majer et al 2007) Therefore it is critical that the policy makers and the general community are assured geothermal technologies relying on fluid injections will be engineered to minimize induced seismicity risks ensuring the resource is developed in a safe and cost effective manner
11 Intended Use The Protocol is intended to be a living document for the public and regulators and geothermal operators This version is intended to supplement the existing International Energy Agency (IEA) protocol (Majer et al 2009) and as practically as possible be kept up-to-date with state-of-the-art knowledge and practices both technical and non-technical As methods experience knowledge and regulations change with respect to induced seismicity so should the Protocol It also recognizes that ldquoone sizerdquo does not fit every geothermal project and not everything presented herein should be required for every EGS project Local conditions at each site will call for different types of action Variations in procedures will result from such factors as the population density around the project past seismicity in the area the size of the project the depth and amount of injection and its relation to any faults etc
This document was prepared at the direction of the U S Department of Energyrsquos Geothermal Technologies Program It is an advisory document intended to assist industry and regulators to identify important issues and parameters that may be necessary for the evaluation and mitigation of adverse effects of induced seismicity Determination of actual site-specific criteria that must be met by a particular project is beyond the scope of this document it remains the obligation of project developers to meet any and all applicable federal state or local regulations
1 INTRODUCTION
2 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
12 Objective
Provide a flexible protocol that puts high importance on safety while allowing geothermal technology to move forward in a cost effective manner
To promote the safety of EGS projects and to help gain acceptance from the general public for geothermal activities in general and EGS projects specifically it is beneficial to clarify the role and risks of induced seismicity which can occur during the development stages of the EGS reservoir and the subsequent extraction of the geothermal energy This document provides a set of general procedures that detail useful steps geothermal project proponents can take to deal with induced seismicity issues The procedures are not prescriptive but suggest an approach to engage public officials industry regulators and the public at large facilitating the approval process helping to avoid project delays and promoting safety
With respect to the existing IEA protocol (Majer et al 2009) this document addresses many of the same issues and others that arose after the protocol was published For example it provides a more accurate approach to address and estimate the seismic risk associated with EGS induced seismic events Regulators the public the geothermal industry and investors need to have a framework to estimate such a risk Another significant change is a shift toward addressing ground motions rather than event magnitudes to measure the impact of seismicity This led to a discussion of the thresholds for vibration which involve not only the amplitude of the ground motions but also such factors as the duration frequency content and other measures of impact Also attention was paid to the legal implications with respect to the impact or effect of any recommended actions Lastly an effort was made to base recommendations on existing and accepted engineering standards that are used in such industries as mining construction or similar activities that produce or have the potential for producing unwanted ground motions and noise
13 Background To access geothermal resources wells are drilled to depths at which the required high temperatures and thermal capacities are reached The depth required to reach that temperature depends upon the temperature gradient (the rate of temperature increase with depth) which varies significantly from place to place Therefore the depths of geothermal wells vary over a wide range from less than 1000 to 5000 meters (m) in rare cases In addition to elevated temperatures a geothermal well for commercial development must also intersect sufficient permeability to enable the extraction andor circulation of fluids at certain flow rates ie at least a sustained production of 5 megawatts (MW) over a 30-year period
The combination of sufficiently high temperature and good natural permeability occurs in certain areas of the earth such as some areas of active tectonism and volcanism However these comprise only a fraction of the earth elsewhere permeability is lower even though the desired temperature may be accessible by drilling In such cases the permeability of the rock must be enhanced to enable commercial flow rates To date the only method of adequate permeability enhancement in EGS is through fluid injection which can have the side-effect of causing induced seismicity In an important way this side-effect is beneficial EGS project developers monitor and map induced seismicity to understand and manage the EGS reservoir The induced event locations show where fractures have slipped slightly in response to increasing pore pressure andor temperature change during injection a process that can increase the aperture and conductive length of some fractures and therefore the permeability of the reservoir Typically monitoring and mapping of induced seismicity is used to help site and target deep wells
The orientation of the fractures that tend to slip most easily in response to fluid injection depends upon the orientation of the ambient stresses acting on the reservoir rock In turn these depend on the regional tectonic framework and the local geologic structure The ease with which fractures slip during injection depends upon the strength of the reservoir rock the magnitudes of the stresses acting on it and the pore pressure increase The size of the seismic event will depend upon the amount of stress available to cause the slip and the dimensions of the slip area Injection may cause thermal contraction which also may play a role The amount of fracture slip (the main cause of induced seismicity in EGS projects) depends upon the interplay between these elements This explains the importance of understanding the geomechanics temperature and hydraulics in EGS planning assessment and development
3
1 INTRODUCTION
3 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
It is noted that there is little if any potential for induced seismicity in geothermal applications where no fluid is injected or withdrawn from the native formations or if the fluids that are injected andor withdrawn are at a shallow depth (less than 300 to 600 m) Therefore such applications as heat pumps and shallow injections are not considered in this EGS Protocol because of the low potential for induced seismicity
In this Protocol we use the terms ldquovibrationrdquo and ldquoground shakingrdquo or ldquoground motionrdquo We use ldquovibrationrdquo when referring to the regulatory aspects of ground motions since vibrations can be and are regulated We use ldquoground shakingrdquo and ldquoground motionrdquo interchangeably when referring to the ground motions resulting from natural earthquakes and induced seismic events We also distinguish between natural tectonic ldquoearthquakesrdquo and ldquoinduced seismic eventsrdquo even though the processes of generation are generally the same
Finally we also note that the terms ldquoinducedrdquo and ldquotriggeredrdquo are often used interchangeably in the literature on induced seismicity and by practitioners in those fields and in the field of seismology In terms of the process of causing a seismic event the two terms should be used differently although admittedly it is difficult to define where an induced seismic event should be called a triggered seismic event and vice versa As an example of the discussion that is ongoing in the induced seismicity community the US Society of Dams has officially adopted the use of the term ldquoreservoir-triggered seismicityrdquo rather than the traditional 50-year old phrase ldquoreservoir-induced seismicityrdquo In this Protocol we use the term ldquoinducedrdquo to include all seismic events that result from fluid injection and will only use the term ldquotriggeredrdquo in well-defined situations A glossary of terms can be found in Appendix C
4 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
5
2 StepS in AddreSSing induced SeiSmicity
5 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
2 Steps In Addressing Induced Seismicity
A series of recommended steps to meet the objective stated above is included below This is not a ldquoone size fits allrdquo approach and stakeholders should tailor their actions to project-specific needs and circumstances
This document outlines the suggested steps a developer should follow to address induced seismicity issues implement an outreach campaign and cooperate with regulatory authorities and local groups With the goal in mind of gaining acceptance by non-industry stakeholders and promoting safety the Protocol is a series of technical steps to inform the project proponent as well as complementary outreach andor education steps to inform and involve the public
The following steps are proposed for addressing induced seismicity issues as they relate to the whole project
Step 1 Perform a preliminary screening evaluation
Step 2 Implement an outreach and communication program
Step 3 Review and select criteria for ground vibration and noise
Step 4 Establish seismic monitoring
Step 5 Quantify the hazard from natural and induced seismic events
Step 6 Characterize the risk of induced seismic events
Step 7 Develop risk-based mitigation plan
The steps above are listed in the order generally expected to be followed but it is anticipated that each developer will organize its own program Regulatory or other requirements may affect the order or approach to undertaking these steps For example when a Federal agency is involved (eg Federal lands funding permitting) compliance with the National Environmental Policy Act (NEPA) may be required This document is not intended to be a substitute for such activities but instead seeks to advise stakeholders who may be involved with such regulatory activities Project proponents should work closely with NEPA compliance officials with the involved Federal agency(ies) to align information needs and public involvement activities with the NEPA review process This also would be true for compliance with other environmental review requirements such as state NEPA-like laws (eg California Environmental Quality Act) and permitting or approval requirements
2 StepS in AddreSSing induced SeiSmicity
6 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
STEP 1
Perform a Preliminary Screening Evaluation
211 Purpose Sources of opposition to projects such as an EGS project often arise from a variety of possible issues ranging from local politics to community preferences or regulations Technical considerations such as those associated with seismic risk although often secondary must also be evaluated to decide if the project can proceed Therefore before going forward in the planning and engineering of an EGS facility the feasibility of such a project and the associated socioeconomic and financial risks must be evaluated to determine whether there are any obvious ldquoshow-stoppersrdquo This first step is therefore a ldquoscreeningrdquo analysis designed to eliminate sites that would present a low probability of success and to confirm those that have manageable risks and remain strong contenders This provides an initial measure of project acceptability and should include consistency with Executive Order 12898 Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations (February 11 1994)
Although not intended to be a complete analysis Step 1 should have enough rigor and credibility to support early technical communications identify potential impacts and establish credible plans to go forward with enough confidence to demonstrate that public and regulatory acceptability is achievable This step focuses on expected ground motion damages and nuisance Its goals are to identify projects that have a low likelihood of technical success or of being accepted by local populationsmdashand to give an opportunity to the responsible developer to make an informed decision as to whether it is viable to proceed and to determine the analysis needs for those projects that do proceed
212 Recommended Approach A bounding type of analysis should be performed to quickly establish the likelihood that the project would obtain regulatory approval to proceed The likelihood should be categorized as one of four levels (I) High-to-very high (II) Medium-to-high (III) Medium-to-low or (IV) Low-to-very low
Potential EGS geographic areas may vary significantly in terms of their populations and the existing level of seismicity The screening analysis for some projects may be quite clear for example a remote site with little natural seismicity would be categorized as a clear Level I and an urban site with active faulting would be a clear Level IV For those projects in all but category Level IV (which should be discarded after initial screening) this process will highlight the areas of risk that need to be addressed
The same general approach to standard risk analysis is suggested for this screening process but with an emphasis on simplicity and using an approximate or qualitative approach rather than the often more onerous quantitative approaches
a Review relevant federal state and local laws and regulations
Generally assess the prospect of proceeding with the project ie determine if the local regulations are so restrictive that any effects of induced seismicity would not be allowed
b Determine the radius of influence within which there could be a negative impact as a result of seismic activity due to EGS
Identify the existing potential seismic hazards for natural seismicity (eg US Geological Survey National Hazard Maps Petersen et al 2008) This radius of influence will be determined by many local factors such as proximity to structures expected seismicity types of structures local geology and expected size of EGS project Estimate the maximum injection-induced seismic event including a realistic maximum estimate of ground motion using similarities with existing EGS projects this will allow a refinement of the radius of influence
7
2 StepS in AddreSSing induced SeiSmicity
Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
c Identify potential impacts including physical damages social disturbances nuisance economic disruption and environmental impacts
d Establish an approximate lower and upper bound of potential damages using both the average expected induced seismicity and the worst case based on 1) the number type and average value of structures impacted and 2) the likely range of ground motion either from observations or from assumed event magnitudes and existing ground motion attenuation relationships
e Based on these results classify the overall risk as one of the four above described categories (Levels I to IV) from which the recommended decision is as follows
I Very Low II Low III Medium IV High
Proceed with planning Can proceed with planning but may require additional analysis to confirm
Probably should not proceed at this site but additional analysis might support proceeding
Do not proceed
Additionally consider and factor in the publicrsquos level of concern regarding the project Therefore the final decision needs to be made after interaction with the local community in recognition of the fact that different communities may have different acceptance levels of risk andor possibly different socioeconomic needs This will allow this risk scale to be calibrated hence outreach and transparency play an important role
If it is decided to proceed with planning the results of the bounding analysis would be presented to the public in the potentially impacted geographical region (as defined in the radius of influence) to facilitate communication and feedback In particular a scientifically credible estimate of the worst-case scenario should be made to quantify its probability of occurrence and to compare the worst-case scenario with events of comparable levels of risk including the risk associated with natural seismicity (See Step 2 which discusses mechanisms for outreach)
At a minimum the following estimates should be included in the screening study
bull A description (location magnitude frequency of occurrence) of the selected natural earthquakes andor induced seismic events considered in the screening study
bull A map of the ground motion people might experience from these earthquakes andor induced seismic event and its frequency of occurrence
bull A description of conditions that could constitute nuisances and what is commonly accepted in other similar cases (mining transportation industrial manufacturing construction etc)
bull The level of impact perceived to be safe by the stakeholders (regulators community operator etc)
bull An estimate of the number of people institutions and industries located in the region that might be exposed to any impact of concern the expected frequency of occurrence and possible mitigation measures
213 Summary Step 1 is an initial screening that should be capable of withstanding regulatory and public scrutiny for the purpose of determining the overall feasibility of the project and identifying possible flaws or circumstances that could become ldquoshow-stoppersrdquo for the EGS project
The recommended process for Step 1 includes the collection of readily available information and scientific and nontechnical information that could be used to assess the potential impact on the communities and stakeholders a simple but rigorous analysis to evaluate the possible minimum impact in routine operations and possible worst-case impact of the proposed project
7
2 StepS in AddreSSing induced SeiSmicity
8 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
STEP 2
Implement an Outreach and Communications Program
221 Purpose Acceptability to the local community is an important milestone in an EGS project It is critical that public stakeholders are kept informed and their input is considered and acted upon as the project proceeds The outreach and communications program is designed to facilitate communication and maintain positive relationships with the local community stakeholders regulators and public safety officials All of these groups are likely to provide their feedback to the geothermal developer at different times during the project
The outreach program should help the project achieve a level of transparency and participation based on the following suggested framework for interaction
bull The project developer should create an outreach plan at the start of the project and periodically update and modify the plan as needed as the project proceeds addressing stakeholder concerns
bull The amount and type of outreach should be related to the specific project situation including distance from population size of the project duration of activities with potential for induced seismicity the regulatory environment and the number and types of entities responsible for public safety
bull The dialogue should be open informative and multi-directional
bull Multiple meetings should be held as the project progresses and more information is obtained
bull Each group (community stakeholders regulators public officials) should be approached at an appropriate technical level A mechanism to respond to their concerns and questions should be put in place and maintained throughout the project
It is expected that there would be many participants in the outreach and communications plan including the project proponents (developer team seismologist civil or structural engineer local utility company and a representative of the funding entity) the community (local project employees community leaders and community members at large) and public safety officials regulators andor organizations (law enforcement fire department emergency medical personnel)
222 Recommended Approach The following list is relatively long and tries to envisage many scenarios in which the public may become involved with an EGS project As for the Protocol itself there is no ldquoone size fits allrdquo approach to outreach and communications and it is expected that project proponents will prepare their own outreach plans that are suitable to the issues at hand All of the following are considered as suggestions only some may not be needed depending on the specifics of the project and the local communities
a Evaluate outreach needs
Identify the people and organizations who would be the outreach targets hold preliminary discussions with community leaders regulators and public safety officials to explain the project and determine their concerns identify individuals (community regulatory and public safety) who have the trust of the community at large and engage them in discussions about the project identify community needs that could be partially or fully met by the EGS project (eg school science programs support to libraries or community facilities supplied by produced geothermal fluids such as a community greenhouses heating systems and swimming pools) consider what the project could reasonably offer the community to increase their involvement appreciation and pride in the project including employment opportunities
9
2 StepS in AddreSSing induced SeiSmicity
9 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
b Develop plans to approach community stakeholders regulators and public safety officials
c Develop a public relations plan to generate interest in the project from local media
d Set up a local office in the community ideally including technical displays for visitors
e Hold an initial public meeting and site visit that covers both technical and non-technical issues
Assume that the audience is well informed and knowledgeable but also be prepared to explain issues in relatively simple terms Explain how the project is funded and introduce the team and its qualifications If applicable explain that public institutions such as the US Geological Survey universities and national labs may also be involved not only as technical help but as independent agencies to check results Begin with an overview of the project and the motivation for doing it then explain the steps in the project and the approximate timeline Explain why induced seismicity may occur and the history of induced seismicity in other applications This may require an explanation of the difference between induced seismicity and natural earthquakes (size frequency etc) Ideally the public would get involved in the discussion through questions and answers ensuring a two-way dialogue with both sides asking and answering questions The developer can ask about any felt seismicity in the past and should be prepared with a historic earthquake catalogue of the area (if available) If events have occurred nearby the developer could ask if specific events were felt or not and if there was any damage
bull During this discussion it can be acknowledged that EGS projects might have implications that are technical (for the project) safety-related (ensuring no danger to life and property) and economic (a path toward an indigenous stable and renewable energy supply jobs) Explain the specific local benefit (jobs school library heating greenhouse swimming pool etc) Explain the analyses already undertaken and the potential risks and advise the public that a procedure is being developed prior to execution to prevent adverse induced seismicity as well as modifying the planned operations if induced seismicity becomes a problem Similarly advise that a procedure is being developed for evaluating damage and that it may require building inspections before any significant geothermal operations take place
bull Explain the benefits of the project both locally and globally If possible provide some images of what the geothermal power plant might look like If any activity is occurring on site use it as part of the technical explanation if there is no activity at the time the meeting is held use that to demonstrate that the fundamental nature of the site will not change very much
bull The developer should listen to concerns and respond openly and ideally would set up mechanisms to notify the community as work proceeds (phone tree e-mail list website etc) and for the community to ask questions and receive answers about the project
f If feasible hold another site visit during a period of active drilling
This will get people interested and involved since drilling activities are genuinely interesting to most people
g Hold another meeting in advance of the first stimulation
Explain the procedure for monitoring induced seismicity the thresholds that have been set for induced seismicity and their rationale the procedure for modifying the stimulation procedure in the event that the community will find the impacts of the induced seismicity intolerable the call-in line (ldquohot linerdquo) that is available for reporting felt events and how calls will be handled and the liaison between the project and public safety officials
h If feasible bring community members to the site when stimulation is occurring so that they can see the simplicity of the operation (water pumping)
i After stimulation hold another meeting to report on the results Explain what happens next and discuss the positive and any negative effects associated with the project to the community
j As additional operations at the site proceed advise the community via the communications network and seek feedback
k Plan and conduct additional meetings and media events as appropriate
2 StepS in AddreSSing induced SeiSmicity
10 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
223 Summary The overarching goal of the outreach and communications program is to engage the community in a positive and open manner before onsite activities begin and continuing as operations proceed The first step is to understand the community and its needs and concerns and then to determine creative ways to inform the community engage them in a dialogue and demonstrate the benefits of the project particularly at the local scale In addition to being an information exchange the outreach and communications program should be designed to engender long-term support for the project To the extent that a project is distant from local population the requirements of the outreach program would decrease
11
2 StepS in AddreSSing induced SeiSmicity
11 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
STEP 3
Review and Select Criteria for Ground Vibration and Noise
231 Purpose The geothermal developer should identify and evaluate existing standards and criteria thus becoming informed of the applicable regulations for ground-borne noise and vibration impact assessment and mitigation that have been developed and applied by other industries and could be helpful in evaluating the EGS project These standards and criteria apply to damage to buildings human activity interference industrialcommercialresearchmedical activity interference and wildlife habitat Existing criteria developed for non-EGS industries may or may not apply specifically to EGS and appropriate acceptance criteria for an EGS project would likely be based on a variety of factors such as land use population frequency of occurrence of EGS events magnitudes etc
232 Recommended Approach Steps for selecting environmental noise and vibration impact criteria are outlined below
a Assess Existing Conditions
Evaluate the existing ground vibration and noise environments in areas of potential impact to establish a baseline Then evaluate the impacts anticipated from the project Absolute vibration or noise limits for EGS seismic events would be at least equal to or more likely greater than that associated with existing natural and cultural background levels
b Review Local Ordinances
Identify local ordinances or requirements that may be appropriate as they relate to noise and vibration or other such disturbances For example noise and vibration from railroads or highways are not subject to local noise ordinances while lawn mowers often are
c Review Building Threshold Cosmetic Damage Criteria
Building damage criteria are usually stated in terms of the peak particle velocity (PPV) (equivalent to the peak ground velocity or PGV) measured at the ground surface (typically the building foundation but more appropriately the ground surface in the free-field) Building damage criteria usually focus on cosmetic damage which includes hairline cracking of paint or stucco where the cracks usually do not remain open
Threshold cracking criteria have been recommended in US Bureau of Mines (USBM) Report RI 8507 (Siskind et al 1980) Although these criteria were developed for blasting and construction activities the seismic energy from these activities would be similar to that from induced seismic events (in frequency bandwidth and range) and thus be applicable to induced seismicity cases These criteria are almost universally used by the construction and mining industry to assess the potential for threshold cracking due to blasting and are employed in many commercially available vibration monitoring systems Transient ground vibration from blasting at mining operations is probably most closely related to EGS-induced seismicity and the USBM criteria for threshold cracking due to blasting would appear to be directly applicable to EGS-induced seismicity
Vibration limits are often applied to construction projects to avoid threshold damage to structures Construction vibration limits may be lower than the USBM criteria possibly for two reasons One is the desire to be conservative in assessing damage risk Another is that construction vibration may involve general earth-moving operations and continuous excitation from sources such as vibratory pile drivers soil compactors and impact pile drivers which may operate for several weeks at a major project Examples of construction vibration limits include those used by the California Department of Transportation (2004) and the Federal Transit Administration (FTA 2006) These construction vibration limits may be less applicable to EGS than the USBM criteria for blasting given in RI 8507
2 StepS in AddreSSing induced SeiSmicity
12 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
d Review Structural Damage Criteria
Local building codes and structure types should be reviewed to determine appropriate ground-motion limits that might be applicable Dowding (1996) suggests that reinforced concrete structures can experience high vibration without damage perhaps as high as 125 to 250 mmsec (5 to 10 insec) peak particle velocity (PPV) These PGVs are considerably higher than thresholds for cosmetic damage Siskind (2000) discusses a number of case histories and experiments that indicate the PGVs at which both cosmetic and structural damage may occur In particular cracking of free-standing masonry walls was found for PGVs of 150 mmsec to 275 mmsec (6 to 11 insec) Continuous exposure of full-scale free-standing concrete masonry unit walls to PGVs of up to 175 mmsec (7 in sec) at 10 Hz for 26 hours did not produce cracking (Siskind 2000)
Soil settlement due to vibration is discussed by Dowding (1996) Pile driving can induce some densification though usually within a distance associated with the length of the pile A review of the literature concerning foundation settlement due to repetitive exposure to ground motions expected for EGS should be conducted Damage criteria for underground structures such as pipelines or basement walls should be reviewed a useful discussion is provided by Dowding (1996)
e Assess Human Exposure to Vibration
Guidelines for assessing human response to vibration are provided in American National Standard Institute (ANSI) S271-1983 (formerly ANSI S329-1983) Guide to the Evaluation of Human Exposure to Vibration in Buildings This standard corresponds to International Organization for Standardization (ISO) 2631 parts 1 and 2 (ISO 2003) The ANSI S271 guidelines include human response curves that define the levels of acceptability for vertical and horizontal third octave velocity and acceleration Dowding (1996) discusses the use of PPV versus ANSI S271 and ANSI S218 criteria for human exposure to vibration
f Assess Interference with Industrial and Institutional Land Uses
Vibration limits for various industrial and institutional activities should be identified The types of industrial and institutional land uses include hospitals university research laboratories biomedical research facilities semiconductor manufacturing facilities recording studios metrology laboratories and the like The Institute for Environmental Sciences (IES 1995) has recommended generic vibration criteria for various types of equipment and instrumentation Where available specifications for specific equipment (such as hospital MRI machines scanning electron microscopes etc) should be relied on
g Assess Ground-Borne Noise
Ground motions produced by an EGS-induced seismic event can produce audible noise inside buildings The FTA provides guidelines for assessing ground-borne noise and vibration impacts from new transit systems (FTA 2006) These criteria may not be directly applicable to EGS but they are likely to be referred to by stakeholders or regulators
233 Summary Numerous criteria standards and equipment specifications exist that may be drawn upon in assessing the impact of EGS seismicity on neighboring communities These should be reviewed in detail and used to develop appropriate criteria for risk assessment Some of the information may be directly applicable to EGS but most would likely require some adjustment considering the short duration and unpredictability of induced seismic events No doubt additional criteria can be found For example European countries where EGS activities have been developed are considering EGS-specific impact assessment criteria or mitigation design provisions
13
2 StepS in AddreSSing induced SeiSmicity
13 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
STEP 4
Establish Local Seismic Monitoring
241 Purpose Gather seismic data from the project area and vicinity to supplement existing seismic data (see Step 5 Section 25) The seismic data will include baseline data collected before operations begin at the site and data collected during operations The seismic data will be used not only to forecast induced seismicity activity but also to understand induced seismicity for mitigation and reservoir management purposes
As will be pointed out in Steps 5 and 6 a main element in forecasting the level of induced seismicity is to determine the baseline level of seismic activity that exists before the project starts That is how will the geothermal project modify existing ldquonaturalrdquo seismicity The amount of available seismic data will vary depending on the project location in many areas it is likely that the available baseline data will be from regional seismic monitoring (with distances between seismic monitoring stations on the order of tens of kilometers if not more) Current experience indicates that geothermal projects (particularly EGS projects) require a high sensitivity to seismicity at low magnitude thresholds (magnitude 0 to 1 range) to enable active seismic zones to be properly identified However regional seismic monitoring is usually only reliable at or above magnitude 20 Also in most cases of geothermal induced seismicity a great majority of the seismicity is below the magnitude 20 level thus it is important to know the baseline level of seismicity at the lower magnitudes Once the natural or baseline seismic data have been collected and evaluated they are typically used for making operational decisions that relate to stress directions seismic source types (faulting types) and other characteristics that will be useful for designing and operating the overall project Finally it is necessary to collect a minimum amount of seismic information to perform the screening step (Step 1) including some information on the frequency of occurrence of natural earthquakes that will be needed to estimate the potential impact on any nearby real-estate andor industrial assets
242 Recommended Approach a The seismic monitoring program should strive to collect data that is not biased in time or space in the vicinity
of the potential geothermal project
The overall objective is to collect enough information to characterize background seismicity and identify any active faults that have the potential to be affected by the EGS activities The length of monitoring time before the injection begins will depend upon the existing information on local seismicity If there is existing monitoring that detects small-magnitude events (in the magnitude 10 range) then the duration of seismic monitoring of the potential injection area may be as short as one month Alternatively in areas with no prior monitoring the duration may need to be as long as six months This implies that one should start monitoring with an array of instruments that has enough elements sensitivity and aperture to capture seismicity in the volume at least twice the radius of the anticipated stimulated (reservoir) volume at magnitudes of as small as magnitude 10 and preferably magnitude 00
b The more sensitive the array of instruments the more detail can be collected on fault structure seismicity rates failure mechanisms and state of stress
These are all needed to not only model and forecast seismicity but also to design the EGS resource development program Evaluating the ongoing natural background seismicity also enables an understanding of the mechanisms of stress buildup and release that may be more easily triggered by fluid injection Ideally bandwidth and dynamic range should be maximized to the extent possible however typical seismic networks for capturing seismicity in these types of applications target the frequency range from a few hertz to several hundred hertz Twenty-four bit resolution is now common at these data rates and should be used in EGS projects Borehole installations of wide-bandwidth sensors are better than surface sensors owing to the increased signal-to-noise ratio and the ability to capture small magnitude events increasing resolution and location accuracy The sensors (surface or borehole) should record three-component data in order to provide complete information on the failure mechanisms and wave propagation (compressional and shear waves) attributes in addition to providing data for more precise locations
2 StepS in AddreSSing induced SeiSmicity
14 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
c The minimum data processing should provide the location magnitude and source mechanisms
More sophisticated analysis such as advanced location schemes (double difference locations tomographic analysis for improved velocity models moment tensor analysis and joint inversions etc) will probably be needed in the operational phases of the project but are unlikely to be needed during the background monitoring phase Procedures for almost all of these methods are available in the public domain To estimate the instrumentation requirements we have defined a ldquotypical geothermal projectrdquo as one or two injection wells and several production wells all located in an area with a diameter of 5 km or less In such a ldquotypicalrdquo project achieving the above objectives requires at least eight three-component stations distributed over and around the area Deep or wider area projects may require more than eight stations keeping in mind that at least five stations are needed to collect enough data to reliably locate events As the project advances and the seismic events are characterized more stations may be needed to ldquofollowrdquo and characterize the seismic activity and utilize the events to develop strategies not only for mitigation of induced seismicity but also for reservoir enhancement and management In certain instances it may be beneficial or required to ldquoin-fillrdquo the main array with temporary stations to increase array sensitivity and achieve better location accuracy and focal mechanism coverage particularly at the time of reservoir creation or when the overall operational strategy is changed The final issue with regard to instrumentation is the decision regarding continuous recording vs triggered recording In any case especially during the injection phase the data should be processed in close to real time for location and magnitude to enable rapid feedback for both technical analyses and any required mitigation
d The monitoring should be maintained throughout the injection activity to validate the engineering design of the injection in terms of fluid movement directions and to guide the operators on optimal injection volumes and rates
Background and local monitoring will also separate any natural seismicity from induced seismicity providing protection to the operators against specious claims and ensuring that local vibration regulations are being followed The local monitoring should include less sensitive recorders that only record ground shaking that can be felt Typically this is achieved by installing a few strong motion recorders near any sensitive structure to record vibrations that may be problematic It is also important to make the results of the local monitoring available to the public in as close to real time as feasible The monitoring should be maintained at a comprehensive level throughout the life of the project and possibly longer however if the rate and level of seismicity decrease significantly during the project consideration can be given to discontinuing the monitoring
243 Summary Seismic monitoring should be commenced as soon as a project site is selected It should be comprehensive enough to allow complete spatial coverage of background or baseline seismicity over an area that is at least twice as large as the largest anticipated enhanced reservoir The monitoring should be maintained for the lifetime of the project and possibly longer depending on seismicity created and volume affected Instrumentation should be able to detect events at least as small as magnitude 10 and preferably to magnitude 00
15
2 StepS in AddreSSing induced SeiSmicity
15 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
STEP 5
Quantify the Hazard from Natural and Induced Seismic Events
251 Purpose Estimate the ground shaking hazard at a proposed EGS site due to natural seismicity and induced seismicity Assessing the ground shaking hazard from natural seismicity will provide a baseline from which to evaluate the additional hazard from induced seismicity Hazard is defined as the result of a physical phenomenon (such as an earthquake or induced seismic event) that can cause damage or loss There are several types of hazards that can result from an earthquake however for induced seismic events we are only concerned with ground shaking and to a much lesser extent noise
The preferred approach to characterizing ground shaking is to characterize it in terms of a quantifiable measure such as acceleration velocity or displacement Instrumental recordings of ground shaking are generally in terms of acceleration or velocity Seismology engineers prefer acceleration because that is the measure they use in their practice In the absence of recording instruments and particularly before the development of seismographs the qualitative measure called ldquointensityrdquo was used in seismology to describe ground shaking In the United States the Modified Mercalli Intensity scale is used However intensity is difficult to equate to acceleration or velocity making it of limited value in evaluating hazard and in engineering
Step 5 should be performed before any geothermal stimulation and operations are initiated Characterization of future induced seismicity at a site is very difficult and assessments must be made based upon the empirical data from other case histories and numerical models which include specific site characteristics
Two approaches can be taken to assess the seismic ground motion at a proposed site a probabilistic seismic hazard analysis (PSHA) and a deterministic seismic hazard analysis (DSHA) Hazard results feed into risk analysis Probabilistic hazard is more useful for risk analysis because it provides the probabilities of specified levels of ground motions being exceeded Scenario-based risk analysis using the results of DSHA is useful to describe potential maximum effects to stakeholders
In typical PSHAs for engineering design the minimum magnitude considered is magnitude 50 because empirical data suggests that smaller events seldom cause structural damage (Bommer et al 2006) Since no EGS-induced earthquake has exceeded magnitude 50 in size to date the hazard analyses should be performed at lower minimum magnitudes The Protocol recommends that PSHAs be performed for magnitude 40 so that the hazard with EGS seismicity can be compared with the baseline hazard To provide input into the risk analysis (Step 6) an even lower minimum magnitude should be considered for nuisance effects or interference with sensitive activities
The ground-motion hazard should be expressed in terms of peak ground acceleration (PGA) acceleration response spectra (to compare with spectra from natural earthquakes and building code design spectra) and PGV Since induced earthquakes are generally small magnitude durations will be short and not of structural concern PGV or PPV will be needed for comparison with cosmetic and structural building damage criteria with criteria for vibration-sensitive research and manufacturing and for human activity interference
2 StepS in AddreSSing induced SeiSmicity
16 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
252 Recommended Approach PSHAs should be performed first for the natural seismicity and then the EGS-induced seismicity should be superimposed on top of that
a Estimate the Baseline Hazard from Natural Seismicity
bull Evaluate historical seismicity and calculate frequency of occurrence of background seismicity based on a catalog of natural earthquakes If baseline seismic monitoring was performed in the EGS geothermal project area incorporate the data into the catalog Account for the incompleteness of the catalog and remove dependent events (eg aftershocks and foreshocks) Examine any focal mechanisms of natural seismicity to assess the tectonic stress field
bull Characterize any active or potentially active faults in the site region and estimate their source parameters (source geometry and orientation rupture process maximum magnitude recurrence model and rate) for input into the hazard analysis The maximum earthquake that can occur on a fault is a function of the available fault area and the amount of displacement that will occur in an event Empirical relationships have been developed that estimate magnitude from rupture length rupture area and maximum and average event displacement
bull For communities that may be impacted by EGS-induced seismicity evaluate the geological site conditions and if practical estimate the shear-wave velocities of the shallow subsurface beneath the potentially impacted communities The shear-wave velocity profile is often used in ground-motion prediction models to quantify site and building foundation responses
bull Select appropriate ground-motion prediction models for tectonic earthquakes for input into the hazard analysis These models are generally based on strong motion data and relate a specified ground-motion parameter (eg PGA) with the magnitude and distance of the causative event and the specific conditions at the potentially affected site(s)
bull Perform a PSHA and produce hazard curves to assess the baseline hazard due to natural seismicity prior to the occurrence of any induced seismicity De-aggregate the hazard results in terms of seismic source contributions
b Estimate the Hazard from Induced Seismicity
Estimating the hazard from induced seismicity is more difficult than for natural seismicity because of the small database of induced seismicity observations both in terms of seismic source characterization and ground-motion prediction However as more information becomes available (particularly seismic monitoring results) the hazard can be re-calculated and the uncertainties reduced Possible steps that should be taken include the following
bull Evaluate and characterize the tectonic stress field based on earthquake focal mechanisms the structural framework of the potential geothermal area and any other available data particularly the results from any prior seismic monitoring To the extent practicable given the available data develop a 3D model of the geothermal area with particular focus on 1) the stratigraphy 2) pre-existing faults and fractures which could be sources of future induced seismicity and 3) the prevailing stress field in which they exist This should include evaluations of drilling results wellbore image logs and any other subsurface imaging data that may exist (eg seismic tomography potential field data)
bull Review known cases of induced seismicity and compare the tectonic and structural framework from those cases with the potential geothermal area In particular examine and compile the information on the maximum magnitude and the frequencies of occurrence of the induced seismicity
bull Evaluate the geologic framework of the project area the characteristics and distribution of pre-existing faults and fractures the tectonic stress field etc (See Step 4 Section 242) This characterization will be useful in assessing the potential and characteristics of future EGS-induced seismicity The best approach to estimating the potential maximum induced earthquake is to characterize the maximum dimensions of pre-existing faults which could rupture in an induced earthquake To be able to estimate fault dimensions imaging faults in the subsurface is required (see Step 1 Section 21 above)
17
2 StepS in AddreSSing induced SeiSmicity
17 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
bull Review and evaluate available models for induced seismicity (eg Shapiro et al 2007 McGarr 1976) that also estimate the maximum magnitude of induced seismicity but based on injection parameters This is an active area of research and there are models being developed as this document is being written The models that are referred to here are only examples and others should be considered Developing a model for induced seismicity is the most challenging task in assessing the hazard Induced seismicity is the interaction between the injection parameters such as injection rates pressures and volume and depth of injection and the in situ stress conditions lithologic structural hydrologic and thermal conditions (eg faults fractures rock strength porosity permeability) These are the most challenging geologic characteristics to evaluate because of the difficulty in imaging and the general heterogeneity and complexity inherent in rock masses Given this challenge conservative assumptions on the maximum induced event and rates of induced seismicity can be made for upper-bound estimates of the hazard Best estimates of the hazard can be improved by incorporating the possible ranges of parameters and their uncertainties In some circumstances an evaluation of the potential for far-field triggering a damaging earthquake on a nearby fault due to fluid-injection induced seismicity may be required although no such cases have been observed to date
bull Review and select empirical ground-motion prediction model(s) appropriate for induced seismicity if any are available or at a minimum one that is appropriate for small to moderate magnitude natural earthquakes (magnitude lt 50) Almost all existing ground-motion models have been developed for magnitude 50 and above natural earthquakes and it has been suggested that there is a break in scaling between small and large earthquakes (Chiou et al 2010) Since the maximum induced earthquake will likely be smaller than magnitude 50 the ground-motion prediction model only needs to be accurate at short distances (less than 10 to 20 km Include the uncertainty in the ground-motion models
bull Calculate scenario ground motions from the maximum induced seismic event by performing a DSHA
253 Summary Compare the hazard results from the natural and induced earthquakes to assess the potential increase in hazard associated with the EGS project The hazard results are fed into Step 6 the risk analysis The hazard estimates should be updated as new information becomes available after injection activities have commenced and if and when induced seismicity has been initiated In particular the results of the seismic monitoring should be evaluated and incorporated into the hazard analyses where possible
2 StepS in AddreSSing induced SeiSmicity
18 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
STEP 6
Characterize the Risk of Induced Seismic Events
261 Purpose The purpose of this step is to develop a rigorous and credible estimate of the risk associated with the design construction and operation of the proposed EGS facility and to compare the future expected risk associated with the operation to the baseline risk existing prior to operation Conceptually this step is the same as Step 1 but instead of aiming at an order of magnitude and a bounding of the risk only for the purpose of screening Step 6 is intended to generate a higher resolution and more precise estimate for the purpose of making decisions on design and operations of the planned EGS It will provide a measure of the variation of risk during future operation and helps in evaluating alternative operational procedures including those that could mitigate the negative effects and minimize the risk of induced seismicity
262 Recommended Approach The standard method (Kaplan and Garrick 1981 US Nuclear Regulatory Commission 1981 Whitman et al 1997 McGuire 1984 Molina et al 2010) of characterizing seismic risk concentrates on the impact of moderate-to-large earthquakes that have greater magnitudes than those generally seen in injection-induced seismicity To date the maximum observed earthquakes attributed to EGS operations have been magnitude 30 to 37 and the largest geothermal injection-related event was magnitude 46 (Majer et al 2007) For all types of fluid injection the largest events have been about magnitude 50 which occurred at the Rocky Mountain Arsenal (Majer et al 2007 Cladouhos et al 2010) The vast majority of EGS induced events are less than magnitude 30 Therefore the dominant risk is associated with events that have low magnitudes and cause low-to-very-low ground motions Consequently the attention to risk will shift relatively from the high-level risk of physical damage associated with large natural earthquakes to the more mundane level of a nuisance and possibly the related economic impacts
The fundamentals of the risk estimation method do not change for small ground motions Physical damages to structures are deemed to be very small to nil but some of the basic elements used to describe the damages will have to account for this shift by for example considering the appearance of small cracks and other minor architectural damages that usually constitute a very small portion of the damage Also human perception of small vibrations and the associated nuisance need to be considered as elements of the risk This nuisance produced by small vibrations is difficult to quantify as it depends not only on the dominant frequency of the vibration but also how frequently it occurs
The elements of a detailed risk analysis are as follows (see example of existing risk-analysis software such as HAZUS 2010 or SELENA 2010)
a Characterize the ground motion at each location within the area potentially impacted (See Step 5 Section 51)
b Identify the assets that could be adversely affected and that could contribute to the total risk
Ground shaking from EGS operations may impact the quality of peoplersquos lives the built environment and the economy in several ways for which the risk needs to be evaluated Contributing to the risk are those elements of our socioeconomic and living environment for which ground-motion impact would be perceived as negative because of its consequences on the financial environmental or personal well-being of the affected community (Mileti 1982) Including all the possible risk contributors would be a daunting task and difficult to achieve and it is reasonable to restrict the range of consideration to the most important areas of concern Some of the impacts to consider are purely physical such as damage to structures and there are well-accepted methods to assess them and to quantify their associated risks usually in monetary terms (see HAZUS SELENA) Other impacts dealing with human perception and sensitivity are more difficult to assess and quantify However there are existing methods albeit not as well established as those associated with damage
19
2 StepS in AddreSSing induced SeiSmicity
19 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Four classes of impacts can be identified as follows
I Physical damage to residential housing and community facilities
Damage to structures would probably be the main concern of any community Much has been published concerning damage from medium-to-large earthquakes (see Applied Technology Council (ATC) publications particularly ATC-3 Tentative Provisions for the Development of Seismic Regulations for Buildings For small magnitude and small ground-motion events the existing information is largely based on USBM research conducted in the 1970s with respect to vibration from controlled blasting (controlled detonation) Damage to the built environment to be considered (eg structures) must be separated into at least two categories 1) minor cosmetic (threshold cracking) and 2) major structural damage
II Physical damage to the infrastructure of industrialcommercialresearchmedical facilities
It is unlikely that strong ground shaking generated by EGS-induced seismic events would occur however stakeholders nevertheless tend to be concerned with infrastructure damage Significant structural damage to infrastructures by EGS is also equally unlikely but should damage occur its assessment should be based on design seismic code requirements and in the absence of such data site visit and observation of structural characteristics Adverse effects should at least be considered for all the vital elements of the infrastructure in the potentially impacted area including industrial facilities (eg manufacturing chemicaloil processing) and research facilities (both industrial and medical)
III Human activity interference
Human activity interference includes interference with sleep conversation enjoyment of recreation or entertainment and the like Of these sleep disturbance is probably the defining activity interference and induced seismicity from EGS activity may occur at any time of day or night Speech interference is not likely as seismicity usually does not radiate sufficient noise to be audible However secondary noise radiation such as squeaking walls may occur and conversations may be suspended in response to perceptible seismic events This can become problematic if it occurs often enough during the course of a day
IV Socioeconomic impact from damaged infrastructure and operation interference in businesses and industrial facilities
Social and economic activity and personal well-being rely heavily on the reliability of complex utility networks (telephone internet water gas electricity public transportation systems) that are vital to conducting business and for maintaining quality of life The potential damage to infrastructure is consequently an important potential contributing component of the risk and any damage leading to operational malfunctions (eg telephone service becoming unavailable) creates interruptions that can be very costly Sometimes very little physical damage can lead to a cascade of network consequences in a ldquodomino effectrdquo particularly (but not exclusively) in communications (eg Internet interruptions leading to the loss of data)
c Characterize the damage potential (vulnerability) from the risk contributors
The potential damages are usually characterized in terms of a relation (called a vulnerability function) that gives the level of damages (physical damage nuisance and economic losses) for that contributor or a class of contributors as a function of the level of the ground motion at a particular location In a detailed probabilistic risk analysis the vulnerability function gives the probability of failure of a structure in response to a particular stimulus (eg a given level of ground motion) Alternatively it gives the average cost of replacement for an entire class (see HAZUS 2010 SELENA 2010 and ATC publications)
d Estimate the risk
The elemental risk associated with one risk contributor at a given location is the product of the damage that would be observed at this location for a given level of seismic ground motion and the probability that this ground-motion level would occur The value of interest is the total risk at this location which is obtained by summing the elemental risks for all possible ground-motion levels using the probabilistic seismic hazard curve developed in Step 5 A risk
2 StepS in AddreSSing induced SeiSmicity
20 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
map or map of expected losses can be obtained by repeating this calculation for all points within the impacted area Usually modern probabilistic risk analyses provide a full probability distribution of the total risk which enables an estimate of the probability that a certain level of risk (monetary loss) will be exceeded In that case if the annual probability of exceedance of risk (losses) of X dollars ($) is p it is customary to say that the ldquoreturn periodrdquo in years of $X of risk (losses) is T=1p years
e Present the results
The general purpose for presenting the results of the risk analysis is to demonstrate that the probable (or a certain percentile) future negative effects of the EGS operation are within a range that will be tolerated by the regulators and community with consideration of the overall benefits of the project as judged by the community and all the stakeholders It is also meant to provide input for comparing benefits and adverse effects on a rational probabilistic and rigorous basis
For this purpose results for all locations in the area impacted need to be presented and displayed in Geographic Information Systems (GIS) map format The results should be separated into a least three categories physical damage nuisance and economic losses At a minimum maps should be developed for each category using a simple calculation of the estimate of the risk Ideally risk maps would be developed for one or several return periods providing useful information on the range of possible risk and contributing to the development of mitigation procedures
The following is a list of possible useful presentation materials
bull Map of region impacted as a function of time (months years decades centuries)
bull Map of short-term (10 to 20 years) probable (expected) impact showing the potential for physical damages These maps will be prepared for several levels of confidence to express the uncertainty in the models
bull Map of short-term impacts in terms of the probable (expected) number of people experiencing ground shaking or exceeding design expectations as a function of time and proximity to the project
bull A map showing the ldquored-flagrdquo locations either because they are specially sensitive or likely to experience high ground motion because of specific local site geological conditions the nature of their business or the fact that they are eg a particularly sensitive node in a socioeconomic system or utility network
bull A table showing the total probable cost by category (physical nuisance economic) each year in the future as a function of time
263 Summary The purpose of Step 6 is to identify the different types of risks and develop a quantitative estimate for each type using well-accepted methods of risk assessment The risk estimates should be revised after each update of the seismic hazard analysis described in Step 6 The estimate of risk should be a function of time and of the various possible future alternative plans of operation of the planned EGS to permit evaluations and comparisons between the alternatives and help in the decision making Results should be presented in ways that account for the nature of the potential risks and the parties that may be affected by the risk in space and time and with estimates of the potential costs associated with the risks
21
2 StepS in AddreSSing induced SeiSmicity
21 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
STEP 7
Develop Risk-Based Mitigation Plan
271 Purpose This step presents some suggested mitigation measures Several types of mitigation can be applied For example direct mitigation might include modifying the injection rates andor production rates Indirect mitigation might include some sort of incentive for the affected community Establishing a bond or insurance policy to mitigate potential liability claims may be a prudent option for an EGS developer It is hoped that by properly carrying out the preceding 6 steps mitigation will not be required in the majority of projects
272 Recommended Approach
a Direct Mitigation
If the level and impacts of seismicity are exceeding original expectations it may be necessary to put mitigation measures in place and establish a means to ldquocontrolrdquo the seismicity One obvious direct mitigation measure is to stop injection This may stop induced seismicity in the long run but because the induced seismicity probably did not start immediately it will not stop immediately That is the stress states have been altered and immediately shutting off the injection without reducing the pressure may cause unexpected results For example in two EGS projects magnitude 30 plus events occurred after the injection well was shot in (Majer et al 2007) This suggests that it may be better to gradually decrease pressures and injections until the designeddesired levels of seismicity are achieved
One system of direct mitigation is a calibrated control system dubbed the ldquotraffic lightrdquo system (Majer et al 2007) This is a system for real-time monitoring and management of the induced seismic vibrations that continuously calculates and plots a cumulative window of the ground motion (usually PGV) as a function of injection rates and time
The boundaries on this traffic light system in terms of guiding decisions regarding the pumping operations are as follows (Majer et al 2007)
bull REDmdashthe lower bound of the red zone is the level of ground shaking at which damage to buildings in the area is expected to set in Pumping suspended immediately
bull AMBERmdashthe amber zone was defined by ground-motion levels at which people would be aware of the seismic activity associated with the stimulation but damage would be unlikely Pumping proceeds with caution possibly at reduced flow rates and observations are intensified
bull GREENmdashthe green zone was defined by levels of ground motion that are either below the threshold of general detectability or at higher ground-motion levels at occurrence rates lower than the already-established background activity level in the area Pumping operations proceed as planned
The major shortcoming of this type of approach is that it does not address the issue of seismicity that occurs after the end of the pumping operation If seismicity exceeding the design levels occurs after all EGS activities stop current knowledge of induced seismicity indicates that the seismicity will stop as the subsurface conditions return to the natural state The time for this to occur will depend on the rate length and volume of injections and withdrawals If seismicity does not subside in a reasonable time (few months) one should consider indirect mitigation activities (see next section) In any case monitoring should continue for at least 6 months beyond the end of the project to determine whether any seismicity is occurring that exceeds background levels before the project began
2 StepS in AddreSSing induced SeiSmicity
22 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
The results of one such application at the Berlin geothermal field in El Salvador (see Majer et al 2007 and Bommer et al 2006) showed that the ground shaking hazard caused by small-magnitude induced seismic events presents a very different problem from the usual considerations of seismic hazard for the engineering design of new structures On the one hand the levels of hazard that can be important particularly in an environment such as rural El Salvador (where buildings are particularly vulnerable owing to their method of construction) are below the levels that would normally be considered of relevance to engineering design As stated previously in PSHA for engineering purposes it is common practice to specify a lower bound of magnitude 50 On the other hand unlike the hazard associated with natural seismicity there is the possibility to actually control the induced hazard at least to some degree by reducing or terminating the activity generating the small events
b Indirect Mitigation
Different methods of indirect mitigation may be considered a few are described below
bull Seismic Monitoringmdashas has been discussed previously in this Protocol seismic monitoring in any potentially affected communities is expected to be part of an adequate EGS development plan The monitoring program should consider the relevant regulations standards and criteria regarding structural damage and noise and the need for building inspections ahead of any EGS operations Although there has been no documented case of damage from induced seismicity caused by fluid injection seismic monitoring and reporting to the public is needed The ideal monitoring program establishes background conditions and permits the evaluation of any EGS-related impact providing a quantitative basis upon which an accurate evaluation of any claims can be made This is fair to both the public and the geothermal developer Evaluating the dominant frequency and PGA or PGV (the variables used to assess structural damage) normally requires the use of surface-mounted seismometers andor accelerometers so these may need to be installed at certain locations in the affected community Continuous seismic monitoring to assess background cultural noise during various parts of the day week andor year is likely to be required Regular reporting should be a matter of course similar to evaluating the effects of blasting during a construction project
bull Increased Outreachmdashalthough it is assumed that the community is already informed about the EGS operations it may be necessary to step up the communication and information flow during certain periods particularly those characterized by any ldquounusualrdquo seismicity This should be done in conjunction with forecasts of trends in seismicity and analyses of the relationships between operational changes and changes in seismicity To the extent that the public is informed about and involved with the project they may be more accepting of the minor and temporary nuisance of induced seismicity
bull Community Supportmdashin addition to jobs a geothermal project may be able to offer other types of support to the local community to help establish good will This can come in almost any form including support for schools libraries community projects and scholarships To the extent that a community support program is established early the public may be favorably disposed toward the project
bull Compensationmdashif any damages can be documented to be caused by the induced seismicity then fair compensation should be made to the affected parties This could be directed toward the community at large perhaps in the form of community grants rather than individuals This is particularly appropriate in the case of trespass and nuisance although it may also be applicable in cases of strict liability and negligence as well The amount of compensation should be negotiated with the affected parties
23
2 StepS in AddreSSing induced SeiSmicity
23 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
c Liability and Insurance
Legal studies specifically related to geothermal-induced seismicity and its effect on man-made structures and public perceptions are rare One of the few studies by Cypser and Davis (1998) that addresses legal issues in the United States related to seismicity induced by dams oil and gas operations and geothermal operations points out the following
Liability for damage caused by vibrations can be based on several legal theories trespass strict liability negligence and nuisance Our research revealed no cases in which an appellate court has upheld or rejected the application of tort liability to an induced earthquake situation However there are numerous analogous cases that support the application of these legal theories to induced seismicity Vibrations or concussions due to blasting or heavy machinery are sometimes viewed as a lsquotrespassrsquo analogous to a physical invasion In some states activities which induce earthquakes might be considered `abnormally dangerousrsquo activities that require companies engaged in them to pay for injuries the quakes cause regardless of how careful the inducers were In some circumstances a court may find that an inducer was negligent in its site selection or in maintenance of the project If induced seismicity interferes with the use or enjoyment of anotherrsquos land then the inducing activity may be a legal nuisance even if the seismicity causes little physical damage
In the course of project planning and implementation an obvious mitigation procedure could be establishing a bond or insurance ldquopolicyrdquo that would be activated as appropriate in the case of induced seismicity
273 Summary Although the risks associated with induced seismicity in EGS projects are relatively low it is nevertheless prudent to consider that some type of mitigation may be needed at some point during the project Therefore the developer should prepare mitigation plans that focus on both the operations themselves and the nuisance or damage that might result from those operations The ldquotraffic lightrdquo system may be appropriate for many EGS operations and provides a clear set of procedures to be followed in the event that certain seismicity thresholds are reached The traffic light system and the thresholds that would trigger certain activities by the geothermal developer should be defined and explained in advance of any operations
Seismic monitoring information sharing community support and direct compensation to affected parties are among the types of indirect mitigation that may be needed Early support from the developer to the community can improve the ability to respond effectively to a potentially impacted community in the event of problematic induced seismicity This may come in the form of jobs or other forms of support that the community specifically needs
24 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
25
3 ACKNOWLEDGEMENTS
25 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
3 Acknowledgements
This work was primarily funded by the Assistant Secretary for Energy Efficiency and Renewable Energy Geothermal Technologies Program of the US Department of Energy under Contract No DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory
26 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
27
4 references
27 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
4 ReferencesAmerican Standards Institute (ANSI) S271-1983 (R2006) (formerly ANSI S329-1983) Guide to the Evaluation of Human Exposure to Vibration in Buildings
Applied Technology Council (ATC) httpwwwatcouncilorgonlinestorehtml
Bommer J J S Oates J M Cepeda C Lindholm J Bird R Torres G Marroquiacuten and J Rivas (2006) ldquoControl of hazard due to seismicity induced by a hot fractured rock geothermal projectrdquo Engineering Geology v 83 pp 287-306
California Department of Transportation 2004 Transportation- and Construction-Induced Vibration Guidance Manual
Chiou B Youngs R Abrahamson N and Addo K 2010 ldquoGround-motion attenuation model for small-to-moderate shallow crustal earthquakes in California and its implications on regionalization of ground-motion prediction modelsrdquo Earthquake Spectra v26 pp 907-926
Cladouhos T Petty S Foulger G Julian B and Fehler M 2010 ldquoInjection induced seismicity and geothermal energyrdquo Geothermal Research Council Transactions v 34 pp 1213-1220
Cypser DA and Davis SD 1998 ldquoInduced seismicity and the potential for liability under US lawrdquo Tectonophysics v 289 pp 239-255
Dowding CH 1996 Construction Vibrations Prentice Hall
Federal Transit Administration (FTA) 2006 Transit Noise and Vibration Impact Assessment FTA-VA-90-1003-06
HAZUS 2010 FEMArsquos Methodology for Estimating Potential Losses from Disasters httpwwwfemagovplanpreventhazus
Institute of Environmental Sciences 1995 Contamination Control Division Recommended Practice Considerations in Cleanroom Design IES-RP-CC0121 Appendix C
International Organization of Standardization (ISO) 2631-2 2003 Mechanical vibration and shock mdash Evaluation of human exposure to whole-body vibration mdash Part 2 Vibration in buildings (1 Hz to 80 Hz)
Kaplan S and Garrick BJ1981 ldquoOn the Quantitative Assessment of Riskrdquo Risk Analysis Vol 1 No 1 pp 11-27
Majer EL Baria R Stark M Oates S Bommer J Smith B and Asanuma H 2007 ldquoInduced seismicity associated with enhanced geothermal systemsrdquo Geothermics v 36 pp 185-222
Majer E Baria R and Stark M (2009) rdquoProtocol for induced seismicity associated with Enhanced Geothermal Systemsrdquo Report produced in Task D Annex I (9 April 2008) International Energy Agency-Geothermal Implementing Agreement (incorporating comments by C Bromley W Cumming A Jelacic and L Rybach) Available at httpwwwiea-giaorgpublicationsasp
McGarr A 1976 ldquoSeismic moments and volume changerdquo J Geophysical Res v 81 pp 1487-1494
McGuire RK 1984 ldquoSeismic Hazard and Risk Analysisrdquo Earthquake Engineering Research Institute Monograph 10 p 221
Mileti D 1982 ldquoPublic perceptions of seismic hazards and critical facilitiesrdquo Bulletin of the Seismological Society of America v 72 pp S13-S18
MIT 2006 The Future of Geothermal Energy ndash Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century MIT Press Boston USA
Molina S DH Lang and CD Lindholm 2010 SELENA ndash ldquoAn open-source tool for seismic risk and loss assessment using logic tree computation procedurerdquo Computer amp Geosciences Vol 36 Issue 3 pp 257-269
Petersen MD Frankel AD Harmsen SC Mueller CS Haller KM Wheeler RL Wesson RL Zeng Y Boyd OS Perkins DM Luco N Field EH Wills CJ and Rukstales KS 2008 Documentation for the 2008 update of the United States National Seismic Hazard Maps US Geological Survey Open-File Report 2008-1128 61 p
SELENA 2010 The SELENA-RISE Open Risk Package downloadable at httpsourceforgenetprojectsselena
Shapiro SA Dinske C and Kummerow J 2007 ldquoProbability of a given-magnitude earthquake induced by a fluid injectionrdquo Geophysical Research Letters v 34 p L22314
Siskind D E 2000 Vibrations from Blasting International Society of Explosives Engineers Cleveland OH USA
Siskind D E Stagg M S Kopp J W and Dowding C H 1980 Structure Response and Damage Produced by Ground Vibration from Surface Mine Blasting US Bureau of Mines Report RI 8507
US Nuclear Regulatory Commission 1981 Fault Tree Handbook NUREG-0492
Whitman RV Anagnos T Kircher C A Lagorio H J Lawson R S and Schneider Pl 1997 ldquoDevelopment of a national earthquake loss estimation methodologyrdquo Earthquake Spectra Vol 13 No 4 pp 643-661
Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
28
29
APPENDIX A BACKGROUND amp MOTIVATION
29 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Appendix A Background and Motivation
Summary To produce economic geothermal energy sufficient fluid heat and permeability must be present in a rock mass In many cases there is sufficient heat especially if one drills deep enough however there is often a need to enhance permeability andor fluid content ie to enhance geothermal systems This could be true in not only new geothermal projects but in existing geothermal projects where one would want to expand current production One of the issues associated with Enhanced Geothermal Systems (EGS) is the effect and role of induced seismicity during the creation or expansion of the underground reservoir and the subsequent long-term extraction of the geothermal energy Induced seismicity has been the cause of delays and possibly cancellation of at least two EGS projects worldwide although to date there have been no or few adverse physical effects on the operations or on surrounding communities from existing geothermal projects Still there is public concern over the possible amount and magnitude of the seismicity associated with current and future geothermal operations One of the more publicized incidents was the magnitude 34 event that occurred in the vicinity of the Basel Switzerland EGS project on December 7 2006 It caused local officials to stop the project and ultimately the project was cancelled This is an example of where a more comprehensive understanding of the type and nature of seismicity would be of benefit to the operators as well as the public
It should also be noted that induced seismicity is not new it has successfully been dealt with in many different environments ranging from a variety of injection and engineering applications including waste and water disposal mining oil and gas and reservoir impoundment (Majer et al 2007) Nevertheless in order to address public and regulatory acceptance as well as maintain industry buy-in of geothermal energy development a set of recommendationsprotocols are needed to be set out on how to deal with induced seismicity issues Presented here are summaries of several case histories in order to illustrate a variety of technical and public acceptance issues It is concluded that EGS induced seismicity needs do not pose any threat to the development of geothermal resources if community issues are properly handled and the operators understand the underlying mechanisms causing the seismicity and develop procedures for mitigating any adverse effects it is perceived to cause In fact induced seismicity by itself provides benefits because it can be used as a monitoring tool to understand the effectiveness of the EGS operations and shed light on the mechanics of the reservoir
Background Naturally fractured hydrothermal systems provide the easiest method of extracting heat from the earth but the total resource and its availability tend to be restricted to certain areas Reasons for pursuing the development of the EGS technology are two-fold (1) to bring uneconomic hydrothermal systems into production by improving underground conditions (stimulation) and (2) to engineer an underground condition that creates a hydrothermal system whereby injected fluids can be heated by circulation through a hot fractured region at depth and then produced to deliver heat to the surface for power conversion The process of enhancing the permeability and the subsequent extraction of energy however may create seismic events In addition to the above-mentioned seismicity at Basel events as small as magnitude 2 and above near certain projects (eg the Soultz project in France Baria et al 2005) have raised residentsrsquo concern for both damage from single events and the effect on seismicity over long time periods as the EGS project continues over many years (Majer et al 2005) Some residents believe that the induced seismicity may cause structural damage similar to that caused by larger natural earthquakes There is also fear and uncertainty that the small events may be an indication of larger events to follow Recognizing the potential of the extremely large geothermal energy resource worldwide and recognizing the possibility of misunderstanding about induced seismicity the Geothermal Implementing Agreement under the International Energy Agency (IEA) initiated an international collaboration The purpose of this collaboration is to ldquopursue an effort to address an issue of significant concern to the acceptance of geothermal energy in general but EGS in particularhellip The objective is to investigate these events to obtain a better understanding of why they occur so that they can either be avoided or mitigatedhelliprdquo
APPENDIX A BACKGROUND amp MOTIVATION
30 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
I Relevant Seismological Concepts and History of Non-Geothermal Induced Seismicity Seismicity has been linked to a number of human activities such as miningrock removal (Richardson and Jordan 2002 McGarr 1976) fluid extraction in oil and gas (Grasso 1992 Segall 1989 Segall et al 1994) waste fluid injection (Raleigh et al 1972) reservoir impoundment (Simpson 1976) and cavity collapses created as a result of an underground nuclear explosion (Boucher et al 1969)
Seismicity in general occurs over many different time and spatial scales Growth faults in the overpressurized zones of the Gulf Coast of the United States are one example of a slowly changing earthquake stress environment as they creep along an active fault zone (Mauk et al 1981) The size of an earthquake (or how much energy is released from one) depends on how much slip occurs on the fault how much stress there is on the fault before slipping how fast it fails and over how large an area its ruptures occur (Brune and Thatcher 2002) Damaging earthquakes (usually greater than magnitude 4 or 5 Bommer et al 2001) require the surfaces to slip over relatively large distances (kilometers) In most regions where there are economic geothermal resources there is usually tectonic activity These areas of high tectonic activity are more prone to seismicity than more stable areas such as the central continents (Brune and Thatcher 2002) Note however that one of the largest earthquakes ever to occur in the United States was the New Madrid series of events the early 1800s in the center of the United States It must also be noted that seismic activity is only a risk if it occurs above a certain level and close enough to an affected community
Large or damaging earthquakes tend to occur on developed or active fault systems In other words large earthquakes rarely occur where no fault exists and the small ones that do occur do not last long enough to release substantial energy Also it is difficult to create a large new fault because there is usually a pre-existing fault that will slip first For example all significant historical activity above magnitude 50 that has been observed in California has occurred on preexisting faults (bulletins of the Seismographic Stations University of California) When large earthquakes occur on previously unknown faults it is generally discovered that these faults already existed but were unmapped as was the case of the Northridge California earthquake (Southern California Earthquake Center httpwwwearthquakecountryinforootssocal-faultshtml)
One last important feature to note regarding earthquake activity is that the size of the fault (in addition to the forces available) and the strength of the rock determine how large an event may potentially be It has been shown that in almost all cases large earthquakes (magnitude 6 and above) start at depths of at least 5 to 10 km (Brune and Thatcher 2002) It is only at depth that sufficient energy can be stored to provide an adequate amount of force to move the large volumes of rock required to create a large earthquake
Water injection seems to be one of the most common causes of induced seismicity Rubey and Hubbert (1959) suggested that a pore pressure increase would reduce the ldquoeffective strength of rockrdquo and thus weaken a fault The seismicity (many events over a 10-year period with the largest having a magnitude of 53) associated with the Rocky Mountain Arsenal fluid disposal operations (injection rates of up to thirty million liters per month over a four-year period) was directly related to this phenomenon involving a significant increase in the pore pressure at depth which reduced the ldquoeffective strengthrdquo of the rocks in the subsurface (Brune and Thatcher 2002) The size rate and manner of seismicity is controlled by the rate and amount of fluid injected in the subsurface the orientation of the stress field relative to the pore pressure increase how extensive the local fault system is and last (but not least) the deviatoric stress field in the subsurface ie how much excess stress there is available to cause an earthquake (Cornet et al 1992 Cornet and Scotti 1992 Cornet and Julien 1993 Cornet and Jianmin 1995 Brune and Thatcher 2002)
31
APPENDIX A BACKGROUND amp MOTIVATION
31 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
II Description of Enhanced Geothermal Systems (EGS) An Enhanced Geothermal System (EGS) is an engineered subsurface heat exchanger designed to either extract geothermal energy under circumstances in which conventional geothermal production is uneconomic or to improve and potentially expand the production operations so that they become more economic Most commonly EGS is needed in cases where the reservoir is hot but permeability is low In such systems permeability may be enhanced by hydraulic fracturing high-rate water injection andor chemical stimulation (Allis 1982 Batra et al 1984 Beauce et al 1991 Fehler 1989) Once the permeability has been increased production can be sustained by injecting water (supplemented as necessary from external sources) into injection wells and circulating that water through the newly created permeability where it is heated as it travels to the production wells As the injected water cools the engineered fractures slippage on the fractures and faults from the induced seismicity and chemical dissolution of minerals may also create new permeability continually expanding the reservoir and exposing more heat to be mined In most EGS and hydrothermal applications the pressures are kept below the ldquohydrofracturerdquo pressure and are designed to induce failure on preexisting fractures and faults ie shear failure on preexisting fractures and faults The idea being that one wants to open an interconnected region of fractures in order to maximize the surface area exposed to the injected fluids which in turn optimizes the heat extraction from the rock
A hydrofracture on the other hand has the potential to create a ldquofast pathrdquo which may not allow an optimal ldquosweeprdquo of injected fluid throughout the rock formation Hydrofractures are used in the oil and gas industry to enhance permeability by creating a large fracture (hundreds of feet long) that connects existing fractures and porosity which will then allow one to ldquodrainrdquo the formation of fluids (oil andor gas) Subsidiary shear failure does occur during the ldquoleak-offrdquo of the fluids from the hydrofracture intersecting the existing fractures (assuming they are oriented in the right direction with the principal stresses) by the same mechanism used in EGS but it is temporary mainly happening only during the hydrofracturing process Thus actual hydrofracturing for geothermal applications may not be as common as in oil and gas applications Other EGS schemes focus on improving the chemistry of the natural reservoir fluid Steam impurities such as noncondensable gases decrease the efficiency of the power plants and acid constituents (principally HCl and H2SO4) cause corrosion of wells pipelines and turbines (Baria et al 2005) Water injection is again an important EGS tool to help manage these fluid chemistry problems
Each of the major EGS techniquesmdashhydrofracturing fluid injection and acidizationmdashhas been used to some extent in selected geothermal fields and in most cases there is some information on the seismicity (or lack thereof ) induced by these techniques Specific examples are summarized below and discussed in detail in Majer et al (2007)
As pointed out and observed injection at sub-hydrofracture pressures can also induce seismicity as documented in a number of EGS projects (Ludwin et al 1982 Mauk et al 1981 OrsquoConnell and Johnson 1991 Stevenson 1985) These studies of low-pressure injection-induced seismicity in geothermal fields have concluded that the seismicity is predominantly of low magnitude The largest recorded event associated with a geothermal operation has been a magnitude 46 at The Geysers field in northern California in the 1980s when production was at its peak Since then there have been more magnitude 4 events but none as large as the event in the early 1980s Almost all other seismicity at other geothermal fields has been in the range of magnitude 3 or less (Majer et al 2007)
Mechanisms of Induced Seismicity in Geothermal Environments
In the geothermal world induced seismicity has been documented in a number of operating geothermal fields and EGS projects In the most prominent cases thousands of earthquakes are induced annually These are predominantly microearthquakes that are not felt by people but also include earthquakes of magnitudes up to the mid-magnitude 4s At other sites the induced seismicity may be entirely of very low magnitudes or may be a short-lived transient phenomenon In the majority of the dozens of operating hydrothermal fields around the world there is no evidence whatsoever of any induced seismicity causing significant structural damage to the surrounding community (Majer et al 2005 Baria et al 2006) However as mentioned above depending on where the geothermal project is located the induced seismicity may still exceed previously agreed-upon levels to any near-by communities for a variety of reasons
APPENDIX A BACKGROUND amp MOTIVATION
32 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Several different mechanisms have been hypothesized to explain these occurrences of induced seismicity in geothermal settings
1 Pore-pressure increase As explained above in a process known as effective stress reduction increased fluid pressure can reduce static frictional resistance and thereby facilitate seismic slip in the presence of a deviatoric stress field In such cases the seismicity is driven by the local stress field but triggered on an existing fracture by the pore-pressure increase In many cases the pore pressure required to shear favorably oriented joints can be very low and vast numbers of microseismic events occur as the pressure migrates away from the well bore in a preferred direction associated with the direction of maximum principal stress In a geothermal field one obvious mechanism is fluid injection Point injection from wells can locally increase pore pressure and thus possibly account for high seismicity around injection wells if there are local regions of low permeability At higher pressures fluid injection can exceed the rock strength actually creating new fractures in the rock (as discussed above)
2 Temperature changes Cool fluids interacting with hot rock can cause contraction of fracture surfaces in a process known as thermoelastic strain As with effective stress the slight opening of the fracture reduces static friction and triggers slip along a fracture that is already near failure in a regional stress field Alternatively cool fluids interacting with hot rock can create fractures and seismicity directly related to thermal contraction In some cases researchers have detected non-shear components indicating tensile failure contraction or spalling mechanisms
3 Volume change due to fluid withdrawalinjection As fluid is produced (or also injected) from an underground resource the reservoir rock may compact or be stressed These volume changes cause a perturbation in local stresses which are already close to the failure state (geothermal systems are typically located within faulted regions under high states of stress) This situation can lead to seismic slip within or around the reservoir A similar phenomenon occurs where solid material is removed underground such as in mines leading to ldquorockburstsrdquo as the surrounding rock adjusts to the newly created void
4 Chemical alteration of fracture surfaces Injecting non-native fluids into the formation (or allowing fluids to flow into the reservoir due to extraction) may cause geochemical alteration of fracture surfaces thus reducing or increasing the coefficient of friction on the surface In the case of reduced friction microearthquakes (smaller events) would be more likely to occur Pennington et al (1986) hypothesized that if seismic barriers evolve and asperities form (resulting in increased friction) events larger than microearthquakes may become more common
All four mechanisms are of concern for EGS applications The extent to which these mechanisms are active within any specific situation is influenced by a number of local and regional geologic conditions that can include the following
a Orientation and magnitude of the deviatoric stress field in relation to existing faults
b Extent of faults and fractures The magnitude of an earthquake is related to the area of fault slippage and the stress drop across the fault Larger faults have more potential for a larger event with a large proportion of the seismic energy being at the dominant frequency of the seismic event related to the length of the shearing fault (ie the larger the fault the lower the emitted frequency which brings it closer to the ranges of frequencies where soils and structures are directly affected and therefore the greater likelihood of structural damage) Large magnitude can also be generated by high stress drop on smaller fault ruptures but the frequency emitted is too high to cause structural damage As a general rule EGS projects should be careful with any operation that includes direct physical contact or hydrologic communication with large active faults
c Rock mechanical properties such as compaction coefficient shear modulus damping and ductility
d Hydrologic factors such as the static pressure profile existence of aquifers and aquicludes rock permeability and porosity
e Historical natural seismicity In some cases induced seismicity has occurred in places where there was little or no baseline record of natural seismicity In other cases exploitation of underground resources in areas of high background seismicity has resulted in little or no induced seismicity Still any assessment of induced seismicity potential should include a study of historical earthquake activity
33
APPENDIX A BACKGROUND amp MOTIVATION
33 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
As stated above several conditions must be met for significant (damaging) earthquakes to occur There must be a fault system large enough to allow significant slip there must be forces present to cause this slip along the fault (as opposed to some other direction) and these forces must be greater than the forces holding the fault together (the sum of the forces perpendicular to the fault plus the strength of the material in the fault) Also as pointed out above the larger earthquakes that can cause damage to a structure usually can only occur at depths greater than 5 km Consequently it is easy to see why the occurrence of large magnitude events is not a common phenomenon In fact a variety of factors must come together at the right time (enough energy stored up by the earth to be released) and in the right place (on a fault large enough to produce a large event) for a significant earthquake to occur It is also easy to see why seismicity may take the form of many small events
III Geothermal Case Histories Several case histories are summarized to demonstrate the different experiences with and the technical and public perception issues encountered with EGS systems These represent a variety of different conditions (but see also Knoll 1992 Guha 2000 Talebi 1998)
The primary issues addressed in these case histories include the following (for details see Majer et al 2007)
Technical Approach
The objective of the injection is to increase the productivity of the reservoir Each case history will have different technical specifications and conditions Important parameters in the design of injection programs are
bull Injection pressure
bull Volume of injection
bull Rate of injection
bull Temperature of fluids
bull Chemistry of fluid
bull Continuity of injection
bull Location and depth of injections
bull In situ stress magnitudes and patterns
bull Fracturepermeability of rocks
bull Historical seismicity
Public Concerns
Each site will also present different levels and types of public concerns Some sites are very remote and thus there is little public concern regarding induced seismicity On the other hand some sites are near or close to urban areas Felt seismicity may be perceived as an isolated annoyance or there may be concern about the cumulative effects of repeated events and the possibility of larger earthquakes in the future
Commonalities and Lessons Learned
In order to recommend how to best mitigate the effects of induced seismicity one must examine the common aspects of the different environments and determine what has been learned to date For example a preliminary examination of data in certain cases has revealed an emerging pattern of larger events occurring on the edges of the injection areas even occurring after injection has stopped In other cases there is an initial burst of seismicity as injection commences but then seismicity decreases or even ceases as injection stabilizes If one can learn from previous EGS projects then past lessons can help prevent future mistakes
APPENDIX A BACKGROUND amp MOTIVATION
34 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
In this study (Majer et al 2007) the case histories included are the following
a The Geysers USA A large body of seismic and productioninjection data have been collected over the last 35 years and induced seismicity has been tied to both steam production and water injection Supplemental injection projects were faced with substantial community opposition despite prior studies predicting less than significant impact The opposition has abated somewhat because of improved communication with residents and actual experience with the increased injection
b Cooper Basin Australia This is an example of a new project that has the potential for massive injection Test injections have triggered seismic events over magnitude 30 The project is however in a remote area and there is little or no community concern
c Berlin El Salvador This was an EGS project on the margins of an existing geothermal field The proponents have developed and implemented a procedure for managing injection-induced seismicity that involves simple criteria to determine whether to continue injection or not This procedure may be applicable to other EGS projects
d Soultz France This is a well-studied example with many types of data collected over the last 15 years in addition to the seismic data EGS reservoirs were created at two depths (3500 m and 5000 m) with the deeper reservoir aimed at proving the concept at great depth and high temperature (200ordmC) Concern about induced seismicity has curtailed activity at the project and no further stimulations are planned until the issue with the local communitymdashassociated with microseismicity and possible damage to structures from an event of around magnitude 29mdashis resolved
IV Gaps in Knowledge As stated above following the six international workshops held on induced seismicity under the auspices of the International Energy Agencyrsquos Geothermal Implementing Agreement (IEA-GIA) DOE and GEISER it has been shown that existing scientific research case histories and industrial standards provide a solid basis for characterizing induced seismicity and the planning of its monitoring Therefore the focus for additional study should be not only on understanding how to mitigate and control the seismicity if necessary but on the beneficial use of induced seismicity as a tool for creating sustaining and characterizing the improved subsurface heat exchangers whose performance is crucial to the success of future EGS projects Following is a list of the primary scientific issues that were discussed at the workshops These are in no particular priority order and are not meant to exclude other issues but were the ones most discussed
1 Do the larger seismic events triggered during EGS operations have a pattern with respect to the general seismicity It was pointed out that at Soultz The Geysers and other sites the largest events tend to occur on the fringes even outside the ldquomain cloudrdquo of events and often well after injection has been stopped Moreover large apparently triggered events are often observed after shut-in of EGS injection operations making such events still more difficult to control The development and use of suitable coupled reservoir fluid flowgeomechanical simulation programs will offer a great help in this respect and advances are being made in this area see for example Hazzard et al (2002) Cornet and Julien (1993) Kohl and Meacutegel (2005) Ghassemi and Tarasovs (2005) By looking at an extensive suite of such models it should be possible to determine what features are correlated to the occurrence of this phenomenon and would eventually allow the development of predictive models of seismicity Laboratory acoustic emission work would greatly help in this effort by complementing the numerical studies and helping to calibrate the models used
2 What are the source parameters and mechanisms of induced events The issue of stress drop versus fault size and moment is important There is some evidence that large stress drops may be occurring on small faults resulting in larger-magnitude events than the conventional models would predict (Brune and Thatcher 2002 and Kanamori and Rivera 2004) It was pointed out that understanding stress heterogeneity may be a key to understanding EGS seismicity Some results support this hypothesis (Baria et al 2005) For example the regional stress field must be determined before any stability analysis is done which (it was concluded) requires integration of various techniques such as borehole stress tests and source mechanism studies It was also found that the existence of induced seismicity does not prove that the rock mass is close to failure it merely outlines local stress concentrations (Cornet et al 1992) In addition it was found that at Soultz it took a 4 to 5 megapascal (MPa) pore-pressure increase over
35
APPENDIX A BACKGROUND amp MOTIVATION
35 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
in situ stress at around 3500 m depth to induce seismicity into a fresh fault that ignores large-scale pre-existing fractures Finally it is difficult to identify the failure criterion of large-scale pre-existing faults many of which do not have significant cohesion
3 Are there experiments that can be performed that will shed light on key mechanisms causing EGS seismicity Over the years of observing geothermal induced seismicity many different mechanisms have been proposed Pore-pressure increase thermal stresses volume change chemical alteration stress redistribution and subsidence are just a few of the proposed mechanisms Are repeating events a good sign or not Does similarity of signals provide clues to overall mechanisms One proposed experiment is to study the injection of hot water versus cold water to determine if thermal effects are the cause of seismicity If we can come up with a few key experiments to either eliminate or determine the relative effects of different mechanisms we would be heading in the right direction
4 How does induced seismicity differ in naturally fractured systems from hydrofracturing environments The variability of natural systems is quite largemdashthey vary from systems such as The Geysers to low-temperature systems each varying in geologic and structural complexity Do similar mechanisms apply and will it be necessary to start afresh with each system or can we learn from each system such that subsequently encountered systems would be easier to address
5 Is it possible to mitigate the effects of induced seismicity and optimize production at the same time In other words can EGS fracture networks be engineered to have both the desirable properties for efficient heat extraction (large fracture surface area reasonable permeability etc) and yet be generated by a process in which the associated induced seismicity does not exceed well-defined thresholds of tolerable ground shaking The traffic light system developed by Bommer et al (2006) goes some way to achieving this end but the idea of fracture network engineering (as introduced in Hazzard et al 2002) should be further investigated Microearthquake activity could be a sign of enhanced fluid paths fracture openingmovement and possibly permeability enhancement (especially in hydrofracture operations) or a repeated movement on an existing fault or parts of a fault The generation of seismicity is a measure of how we are perturbing an already dynamic system as a result of fluid injection or extraction
6 Does the reservoir reach equilibrium Steady state may be the wrong term but energy can be released in many different ways Steamhot water releases energy as does seismicity creep subsidence etc (local and regional stress are the energy inputs or storage) It has been pointed out that while the number of events at The Geysers is increasing the average energy release (as measured by cumulative magnitude of events) is actually constant or slightly decreasing (Majer and Peterson 2005) If this decrease in energy occurs as the result of many small events then this is good if it occurs as the result of a few big events then this is undesirable Thus an understanding of magnitude distribution in both space and time is necessary
V Summary and ConclusionsWay Forward At least six international workshops that have been convened in the last four years to date to address the issue of EGS-induced seismicity have come to the conclusion that induced seismicity poses little threat to produce damaging seismicity but it must be taken seriously and dealt with to make the project acceptable to regulators and any affected communities If properly planned and executed it should not pose any threat to the overall development of the geothermal resources In fact induced seismicity provides a direct benefit because it can be used as a monitoring tool to understand the effectiveness of the EGS operations and shed light on the mechanics of the reservoir It was pointed out many times in these workshops that even in nongeothermal cases where there has been significant induced seismicity (reservoir impoundment (Koyna) hydrocarbon production (Gazli) and waste disposal activities (Rocky Mountain Arsenal Hoover and Dietrich 1969 and Hsieh and Bredehoft 1981)) effects of induced seismicity has been dealt with in a successful manner as not to hinder the objective of the primary project
During these workshops scientists and engineers working in this field have guided us toward a short- and long-term path The short-term path is to ensure that there is open communication between the geothermal energy producer and the local inhabitants This involves early establishment of a monitoring and reporting plan communication of the plan to the affected community and diligent follow-up in the form of reporting and meeting commitments The establishment of good working relationships between the geothermal producer and the local inhabitants is essential Adoption of best
APPENDIX A BACKGROUND amp MOTIVATION
36 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
practices from other industries should also be considered For example in the Netherlands gas producers adopt a good neighbor policy based on a proactive approach to monitoring reporting investigating and if necessary compensating for any damage (see NAM 2002) Similarly geothermal operators in Iceland have consistently shown that it is possible to gain public acceptance and even vocal support for field development operations by ensuring that local inhabitants see the direct economic benefit of those activities (Gudni Axelsson personal communication)
The long-term path must surely be the achievement of a step-change in our understanding of the processes underlying induced seismicity so that any associated benefit can be correctly applied and thus reduce any risk At the same time subsurface fracture networks with the desired properties must be engineered Seismicity is a key piece of information in understanding fracture networks and is now routinely being used to understand the dynamics of fracturing and the all-important relationship between the fractures and the fluid behavior Future research will be most effective by encouraging international cooperation through data exchange sharing results of field studies and research at regular meetings and engaging industry in the research projects Additional experience and the application of the practices discussed above will provide further knowledge helping us to successfully utilize EGS-induced seismicity and achieve the full potential of EGS
References for Appendix A Allis RG (1982) ldquoMechanisms of induced seismicity at The Geysers geothermal reservoirrdquo California Geophys Res Lett 9 629
Baria R S Michelet J Baumgaumlrtner B Dyer J Nicholls T Hettkamp D Teza N Soma H Asanuma J Garnish and T Megel (2005) ldquoCreation and mapping of 5000 m deep HDRHFR Reservoir to produce electricityrdquo Proceedings Paper 1627pdf World Geothermal Congress 2005 Antalya Turkey April 24ndash29 2005
Baria R E Majer M Fehler N Toksoz C Bromley and D Teza (2006) ldquoInternational cooperation to address induced seismicity in geothermal systemsrdquo Thirty-First Workshop on Geothermal Reservoir Engineering Stanford University Stanford California January 30-February 1 2006 SGP-TR-179
Batra R JN Albright and C Bradley (1984) ldquoDownhole seismic monitoring of an acid treatment in the Beowawe Geothermal Fieldrdquo Trans Geothermal Resources Council 8 479
Beauce A H Fabriol D LeMasne CCavoit P Mechler and X K Chen (1991) ldquoSeismic studies on the HDR Site of Soultz-forets (Alsace France)rdquo Geotherm Sci Tech 3 239
Bommer JJ G Georgallides and IJ Tromans (2001) ldquoIs there a near field for small-to-moderate-magnitude earthquakesrdquo Journal of Earthquake Engineering 5(3) 395ndash423
Bommer J J S Oates J M Cepeda C Lindholm J Bird R Torres G Marroquiacuten and J Rivas (2006) ldquoControl of hazard due to seismicity induced by a hot fractured rock geothermal projectrdquo Engineering Geology 83(4) 287ndash306
Boucher G A Ryall and AE Jones (1969) ldquoEarthquakes associated with underground nuclear explosionsrdquo J Geophys Res 74 3808
Brune J and W Thatcher (2002) International Handbook of Earthquake and Engineering Seismology V 81A Intl Assoc Seismology and Phys of Earthrsquos Interior Committee on Education pp 569ndash588
Cornet FH and Yin Jianmin (1995) ldquoAnalysis of induced seismicity for stress field determinationrdquo Pure and Applied Geophys 145 677
Cornet FH and O Scotti (1992) ldquoAnalysis of induced seismicity for fault zone identificationrdquo Int J Rock Mech Min Sci amp Geomech Abstr 30 789
Cornet FH Y Jianmin and L Martel (1992) ldquoStress heterogeneities and flow paths in a granite Rock Massrdquo Pre-Workshop Volume for the Workshop on Induced Seismicity 33rd US Symposium on Rock Mechanics 184
Cornet FH and P Julien (1993) ldquoStress determination from hydraulic test data and focal mechanisms of induced seismicityrdquo Int J Rock Mech Min Sci amp Geomech Abstr 26 235
Cypser DA SD Davis (1998) ldquoInduced seismicity and the potential for liability under US lawrdquo Tectonophysics 289(1) 239ndash255
Fehler M(1989) ldquoStress control of seismicity patterns observed during hydraulic fracturing experiments at the Fenton Hill hot dry rock geothermal energy site New Mexicordquo International J of Rock Mech and Mining Sci amp Geomech Abstracts V 26 p 211- 219
Ghassemi A and S Tarasovs (2005) ldquoA three-dimensional study of the effects of thermo-mechanical loads on fracture slip in enhanced geothermal reservoirsrdquo Submitted to International Journal of Rock Mech Min Sci amp Geomech
37
APPENDIX A BACKGROUND amp MOTIVATION
37 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Grasso J (1992) ldquoMechanics of seismic instabilities induced by the recovery of hydrocarbonsrdquo Pure amp Applied Geophysics 139 507
Guha SK (2000) Induced Earthquakes Kluwer Academic Publishers Dordrecht The Netherlands
Hazzard JF RP Young and SJ Oates (2002) ldquoNumerical modeling of seismicity induced by fluid injection in a fractured reservoirrdquo Mining and Tunnel Innovation and Opportunity Proceedings of the 5th North American Rock Mechanics Symposium Toronto Canada 1023-1030 University of Toronto Press
Hoover DB and JA Dietrich (1969) ldquoSeismic activity during the 1968 test pumping at the Rocky Mountain Arsenal disposal wellrdquo US Geological Survey Circular 613
Hsieh PA and JD Bredehoft (1981) ldquoA reservoir analysis of the Denver earthquakes a case of induced seismicityrdquo J Geophys Res 86 (B2) 903-920
Kanamori H and L Rivera (2004) ldquoStatic and Dynamic Scaling Relations for Earthquakes and their implications for Rupture Speed and Stress Droprdquo Bull Seismol Soc Am v 94 no 1 p 314-319
Knoll P (Ed) (1992) Induced Seismicity AA Balkema Rotterdam The Netherlands
Kohl T and T Meacutegel (2005) ldquoCoupled hydro-mechanical modelling of the GPK3 reservoir stimulation at the European EGS site Soultz-Sous-Foretsrdquo Proceedings Thirtieth workshop on Geothermal Reservoir Engineering Stanford University Stanford California January 31-February 2 2005
Ludwin RS V Cagnetti and CG Bufe (1982) ldquoComparision of seismicity in the Geysers geothermal area with the surrounding areardquo Bulletin Seismol Soc Am 72 863
Majer EL and JE Peterson (2005) ldquoApplication of microearthquake monitoring for evaluating and managing the effects of fluid injection at naturally fractured EGS Sitesrdquo GRC Transactions 29 103ndash107
Majer E R Baria and M Fehler (2005) ldquoCooperative research on induced seismicity associated with enhanced geothermal systemsrdquo Geothermal Resources Council Transactions 29 GRC 2005 Annual Meeting Sept 25ndash28 2005
Majer EL Baria R Stark M Oates S Bommer J Smith B and Asanuma H 2007 Induced seismicity associated with enhanced geothermal systems Geothermics v 36 p 185-222
Mauk F GG Sorrells and B Kimball (1981) ldquoMicroseismicity associated with development of Gulf Coast geopressured-geothermal wells Two studies Pleasant Bayou No 2 and Dow LR Sweezy No 1rdquo Geopressured-Geothermal Energy 105 (Proc 5th US Gulf Coast Geopressured-Geothermal Energy Conf DG Bebout and AL Bachman eds)
McGarr A (1976) ldquoSeismic moment and volume changerdquo J Geophys Res 81 1487
NAM (2002) Aardtrillingen Nederlandse Aardolie Maatschappij (NAM) public information leaflet available from wwwnamnl September 2002
OrsquoConnell DRH and LR Johnson (1991) ldquoProgressive Inversion for Hypocenters and P Wave and S Wave Velocity Structure Application to the Geysers California Geothermal Fieldrdquo Journal of Geophysical Research v 96 B4 6223-6236 doi10102991JB00154
Pennington WD SD Davis SM Carlson J DuPree and TE Ewing (1986) ldquoThe evolution of seismic barriers and asperities caused by the depressuring of fault planes in oil and gas fields of South Texasrdquo Bull of the Seismological Soc of America 76(4) 939ndash948
Raleigh CB JH Healy and JD Bredehoeft (1972) ldquoFaulting and crustal stress at Rangely Coloradordquo AGU Geophysical Monograph 16 275ndash284
Richardson E and T Jordan (2002) ldquoSeismicity in deep gold mines of South Africa Implications for tectonic earthquakesrdquo Bulletin of the Seismological Society of America 92(5) 1766ndash1782
Ruby W W and Hubbert M K 1959 ldquoRole of pore pressure in mechanics of overthrust faulting IIrdquo ldquoOverthrust belt in geosynclinals area of western Wyoming in light of fluids pressure hypothesisrdquo GSA Bulletin V 70 no 2 p 167-206
Segall P (1989) ldquoEarthquakes triggered by fluid extractionrdquo Geology 17 942ndash946
Segall P JR Grasso and A Mossop (1994) ldquoPoroelastic stressing and induced seismicity near the Lacq gas field southwestern Francerdquo Jour Geophys Res 99 15423ndash15438
Simpson DW (1976) ldquoSeismicity changes associated with reservoir loadingrdquo Engineering Geology 10 123
Stevenson DA (1985) ldquoLouisiana Gulf Coast seismicity induced by geopressured-geothermal well developmentrdquo 6th Conf Geopressured-Geothermal Energy 319 (MH Dorfman amp RA Morton ed 1985)
Talebi S (Ed) 1998 Seismicity Associated with Mines Reservoirs and Fluid Injection Birkhaumluser Verlag Basel
Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems38
39
APPENDIX B LIST OF AcrOnymS
39 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Appendix B List of Acronyms
ANSI American National Standard Institute
ATC Applied Technology Council
DSHA Deterministic Seismic Hazard Analysis
EGS Enhanced Geothermal System
GIS Geographic Information Systems
IES Institute for Environmental Sciences
ISO International Organization for Standardization
FTA Federal Transportation Administration
km Kilometer
m Meter
MRI Magnetic Resonance Imaging
MW Megawatt
PGA Peak Ground Acceleration
PGV Peak Ground Velocity
PPV Peak Particle Velocity
PSHA Probabilistic Seismic Hazard Analysis
USBM US Bureau of Mines
40 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
41
APPENDIX C Glossary oF TErMs
41 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Appendix C Glossary of Terms
Amplitude Peak-to-peak measure of a parameter associated with a seismic wave or vibration (eg displacement velocity) usually refers to the level or intensity of ground shaking or vibration
Average annual value Amount of damage per causative event multiplied by the annual probability of occurrence of such events summed over all possible earthquakes and all possible consequences of each earthquake
Deterministic seismic hazard analysis Estimation of the hazard from a selected scenario earthquake or seismic event
Earthquake Result of slip or displacement on a geologic fault resulting in the release of seismic energy Some earthquakes can be ldquoinducedrdquo as a result of a man-made activity eg fluid injection
Enhanced Geothermal Systems (EGS) Activities undertaken to increase the permeability in a targeted subsurface volume via injecting and withdrawing fluids into and from the rock formations that is intended to result in an increased ability to extract energy from a subsurface heat source
Fault mechanism Description of the rupture process of an earthquake ie style of faulting and the rupture fault plane on which it occurs
Focal mechanism Graphic representation of the faulting mechanism of an earthquake calculated by seismologists
Ground-motion prediction model Relationship usually based on strong motion data that predicts the amplitude of a specified ground-motion parameter eg peak ground acceleration (PGA) as a function of magnitude distance and site conditions
Human response curves Graphic representation of a humanrsquos sensitivity and response to vibration as a function of frequency
Induced seismic event Seismic event eg an earthquake that is induced by manmade activities such as fluid injection reservoir impoundment mining and other activities The term ldquoinducedrdquo has been used to include ldquotriggered seismic eventsrdquo and so sometimes the terms are used interchangeably See ldquotriggered seismic eventsrdquo below and in this report
Moment magnitude Preferred method to calculate the magnitude of an earthquake or seismic event based on its seismic moment Seismologists regard moment magnitude as a more accurate estimate of the size of an earthquake than earlier scales such as Richter local magnitude Moment magnitude and Richter local magnitude are roughly equivalent at magnitudes less than 70
Peak ground acceleration (PGA) Maximum instantaneous amplitude of the absolute value of the acceleration of the ground
Peak particle velocity (PPV) Maximum instantaneous amplitude of the absolute value of the velocity of an object or surface
Peak ground velocity (PGV) Maximum instantaneous amplitude of the absolute value of the velocity of the ground
Probabilistic seismic hazard analysis Probabilistic estimation of the ground motions that are expected to occur or be exceeded given a specified annual frequency or return period
Probability of exceedance Probability or more accurately the frequency at which the value of a specified parameter is equaled or exceeded
Quad Unit of energy equal to 1015 BTU 1055 x 1018 Joule and 29307 Terrawatt-hours
Rock permeability Ability of a rock to transmit fluids (oil water gas etc)
APPENDIX C Glossary oF TErMs
42 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Seismic hazard Effect of an earthquake that can result in loss or damage such as ground shaking liquefaction and landslides
Seismic hazard curve Result of a probabilistic seismic hazard analysis The probabilistic hazard is expressed as the relationship between some ground-motion parameter eg PGA and annual exceedance probability (frequency) or return period
Seismic risk Probability of loss or damage due to seismicity
Shear-wave velocity profile Relationship between the shear-wave velocity of the earth and depth Shear-wave velocities of the near-surface (top hundreds of meters) of the ground control the amplification of incoming seismic waves resulting in frequency-dependent increases or decreases in the amplitudes of ground shaking
Spectral frequency Frequencies that constitute the ground-motion record They are the frequencies for which it is necessary to know the energy they carry to be able to reconstitute the full record in the time domain
Tectonic stresses Stresses in the earth due to geologic processes such as movement of the tectonic plates
Temperature gradient Physical quantity that describes (in this context) the change in temperature with depth in the earth The temperature gradient is a dimensional quantity expressed in units of degrees (on a particular temperature scale) per unit length (eg ordmCkm)
Thermal contraction Contracting response of hot materials when interacting with cool fluids
Tomography Imaging by sections or sectioning through the use of any kind of penetrating wave A device used in tomography is called a tomograph while the image produced is a tomogram
Transient ground vibration Temporarily sustained ground vibration
Triggered seismic event Seismic event that is the result of failure along a preshyexisting zone of weakness eg a fault that is already critically stressed and is pushed to failure by a stress perturbation from natural or manmade activities
Vibration Dynamic motion of an object characterized by direction and amplitude
Vibration exposure Personrsquos exposure to vibrations in this case ground-motion vibrations
Vulnerability function Function that characterizes potential damages in terms of a relation that gives the level of consequence (damage nuisance economic losses) as a function of the level of the ground motion at a particular location
APPENDIX D workshop pArTICIpANTsrEVIEwErs
Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Appendix D Workshop ParticipantsReviewers
Affiliation Name Affiliation Name
AltaRock Energy Joe Iovenitti Massachusetts Institute Michael Fehler
Will Osborn of Technology
Anderson Springs Community Alliance
Jeff Gospe Michigan Technological University
Wayne Pennington
Northern California Bill Smith APEX Ken Maher Power Agency
Bureau of Land Management
Linda Christian People Wise Lucy Fine
Calpine Corporation Mark Walters Savy Risk Consulting Jean Savy
Melinda Wright Southern Methodist University
Brian Stump
Rosemary Antonopoulos Stanford University Mark Zoback
Consultant John R Haught
Cumming Geoscience William Cumming
Friends of Cobb Mt Hamilton Hess
GeothermEx Inc Ann Robertson-Tait
Institute of Earth Science Mike Hasting and Engineering (NZ)
Lake County Mark Dellinger Special Districts
Lawrence Berkeley National Lab
Bob Budnitz
Ernie Majer
Larry Hutchings
Larry Myer
Mack Kennedy
Pat Dobson
Lawrence Livermore Bill Foxall National Lab
The University of Texas Cliff Frohlich at Austin
US Department of Energy Alexandra Pressman
Alison LaBonte
Avi Gopstein
Brian Costner
Chris Carusona
Christy King-Gilmore
Douglas Kaempf
Jay Nathwani
Lauren Boyd
US Geological Survey Art McGarr
Dave Oppenheimer
Steve Hickman
URS Corporation Ivan Wong
Los Alamos National Lab James Ruthledge Wilson Ihrig amp Associates Jim Nelson
43
43
44 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
45
APPENDIX E RElEVANT WEbsiTEs
45 Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems
Appendix E Relevant Websites
US Department of Energyrsquos Geothermal Technologiesrsquo Program
httpwwweereenergygovgeothermal
Original Induced Seismicity Protocol
httpesdlblgovfilesresearchprojectsinduced_seismicityegsEGS-IS-Protocol-Final-Draft-20110531pdf
IEA-GIA Induced Seismicity Protocol
httpwwwiea-giaorgdocumentsProtocolforInducedSeismicityEGS-GIADoc25Feb09pdf
Lawrence Berkeley National Labrsquos Induced Seismicity Website
httpesdlblgovresearchprojectsinduced_seismicity
Primer on EGS Induced Seismicity
httpesdlblgovfilesresearchprojectsinduced_seismicityegsprimeregspdf
- -
EERE Information Center For information on the 1-877-EERE-INFO (1-877 337 3463) Geothermal Technologies Program wwweereenergygovinformationcenter visit geothermalenergygov
January 2012 | DOEEE-0662
Appendix B EGS Best Practices
This page intentionally left blank
VERSION APRIL 8 2016
Best Practices for Addressing Induced Seismicity Associated With Enhanced
Geothermal Systems (EGS)
By
Ernie Majer Lawrence Berkeley National Laboratory Berkeley CA 94720 James Nelson Wilson Ihrig amp Associates Emeryville CA 94608 Ann Robertson-Tait GeothermEx Inc Richmond CA 94806
Jean Savy Savy Risk Consulting Oakland CA 94610 Ivan Wong URS Corporation Oakland CA 94612
ONE
TWO
THREE
TABLE OF CONTENTS
Abbreviations vi
Glossaryviii
Units xiv
Forewordxv
Section 1 Step 1 Preliminary Screening Evaluation1-1
11 Purpose 1-1 12 Guiding Principles for Site Screening 1-1 13 Evaluate Risks With Simple Bounding Methods 1-2
131 Local State and Federal Governmentsrsquo Acceptance Criteria 1-3
132 Impact On Local Community 1-3 133 Natural Seismicity and Associated Long-Term Seismic
Risk1-4 134 Magnitude and Location of Worst Case Induced
Earthquake and Associated Risk 1-4 135 Assessing the Overall Risk of the Planned EGS 1-5 136 Identify Main Possible Risk-Associated Reasons for Not
Completing a Project 1-5 14 EGS Project Benefits 1-6 15 Documentation for Initial Project Phase Decision Making1-6
151 Full Technical Documentation 1-6 152 Summary Evaluation of the Risk1-6
16 Case Studies1-7
Section 2 Step 2 Outreach and Communications2-1
21 Purpose 2-1 22 Main Elements2-1 23 Examples 2-2
231 Other Industrial Projects2-2 232 EGS Projects2-6 233 Project Near a Community 2-6 234 Project Distant From a Community2-8
24 Recommended Approach 2-9 25 Summary2-11
Section 3 Step 3 Criteria for Damage Vibration and Noise3-1
31 Purpose 3-1 32 Building Damage Criteria3-2
321 Threshold Cracking 3-3 322 Minor and Major Damage 3-10
33 Damage Criteria for Civil Structures3-10
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 ii
FOUR
FIVE
TABLE OF CONTENTS
34 Damage Criteria for Buried Structures3-11 341 Wells3-11 342 Pipelines 3-11 343 Basement Walls 3-12 344 Tunnels 3-12
35 Landslide and Rockslide3-13 36 Human Response 3-13
361 Third Octave Filters3-13 362 Vibration3-14 363 Ground-Borne Noise 3-25
37 Laboratory and Manufacturing Facilities 3-27 371 Criteria 3-27
38 Summary3-30 39 Suggested Reading 3-31
Section 4 Step 4 Collection of Seismicity Data4-1
41 Purpose 4-1 42 Gathering Data to Establish BackgroundHistorical Seismicity
Levels Regional 4-1 421 Possible Sources of Background Data4-2 422 Data Requirements 4-2
43 Local Seismic Monitoring 4-4 431 Basic Requirements 4-4 432 Instrumentation Needs and Data Coverage 4-5 433 Instrumentation and Deployment 4-6 434 Data Archiving and Processing Requirements 4-9
44 Summary4-11 45 Suggested Reading 4-11
Section 5 Step 5 Hazard Evaluation of Natural and Induced Seismic Events 5-1
51 Purpose 5-1 52 Overview of Approach 5-2
521 Estimate the Baseline Hazard From Natural Seismicity 5-2 522 Estimate the Hazard From Induced Seismicity 5-2
53 PSHA Methodology and Computer Programs 5-3 531 Evaluate Historical Seismicity 5-3 532 Characterize Seismic Sources5-5 533 Areal Sources5-8 534 Characterize Site Conditions 5-8 535 Select Ground Motion Prediction Models 5-9 536 PSHA Products 5-9
54 Additional Steps In Characterizing EGS for PSHA 5-10 541 Characterize Local and Regional Stress Field5-11 542 Develop 3D Geologic Model5-11 543 Review of Relevant EGS Case Histories5-11
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 iii
SIX
SEVEN
TABLE OF CONTENTS
544 Develop Induced Seismicity Model 5-11 545 Select Ground Motion Prediction Models for Induced
Seismicity 5-13 546 Products 5-13
55 Summary5-13 56 Suggested Reading 5-13
Section 6 Step 6 Risk Informed Decision Analysis and Tools for Design and Operation of EGS6-1
61 Purpose 6-1 62 Overview of Best Practice Approach 6-1
621 Hazard Vulnerability and Exposure 6-1 622 General Framework of a Best-Practice Risk Analysis for
EGS6-2 63 Seismic Hazard Characterization for Risk Assessment6-4
631 Probabilistic and Scenario Hazard6-4 632 Size of the Assessment Area 6-4 633 Minimum Magnitude of Interest 6-5 634 Time Dependence 6-5
64 Vulnerability and Damage Characterization of Elements Contributing to the Seismic Risk6-5 641 General Development of Vulnerability Functions 6-7 642 Residential and Community Facility Building Stock6-7 643 Industrial Commercial Research and Medical Facilities6-7 644 Infrastructure 6-8 645 Socioeconomic Impact and Operation Interference In
Business and Industrial Facilities 6-8 646 Nuisance 6-8
65 Available Tools Needed Data and Available Resources 6-9 651 HAZUS6-9 652 SELENA6-10 653 RiskScape 6-10 654 CRISIS6-10 655 OpenRisk 6-11 656 QLARM6-11
66 Presentation of Results Needed for Risk-Informed EGS Decision-Making6-11 661 Seismic Risk Associated With Natural Seismicity6-12 662 Seismic Risk Associated With EGS Operation 6-12
67 Summary6-12 68 Suggested Reading 6-12
Section 7 Step 7 Risk-Based Mitigation Plan7-1
71 Purpose 7-1 72 Recommended Approach 7-1
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 iv
EIGHT
NINE
TABLE OF CONTENTS
721 Direct Mitigation 7-1 722 Indirect Mitigation7-3 723 Receiver Mitigation 7-4 724 Liability 7-5 725 Insurance7-5
73 Summary7-6
Section 8 Acknowledgements 8-1
Section 9 References9-1
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 v
ABBREVIATIONS
1-D one-dimensional 3-D three-dimensional
ANSI American National Standards Institute ATC Applied Technology Council
BLM Bureau of Land Management BRGM Bureau de Recherches Geologiques et Miniegraveres
CCS Carbon capture and sequestration DC direct current
DOENETL Department of Energy National Energy Technology Laboratory DSHA deterministic seismic hazard analysis
EGS enhanced geothermal system FEMA Federal Emergency Management Agency
GIS geographic information systems GPL GNU Public License
GPS global positioning system HAZUS-MH HAZUS-Multi-Hazard
IES Institute of Environmental Sciences ISO International Standard Organization
KML Keyhole Markup Language M (earthquake) moment magnitude
MDR mean damage ratio MRI magnetic resonance imaging ndash machine or picture
NEPA National Environmental Policy Act NIBS National Institute of Building Sciences
NRC Nuclear Regulatory Commission Pa Pascal (unit of pressure or stress)
PEER Pacific Earthquake Engineering Research PGA peak ground acceleration
PGV peak ground velocity PPV peak particle velocity
PSHA probabilistic seismic hazard analysis
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 vi
RMS root-mean-square SCEC Southern California Earthquake Center
SEM scanning electron microscope SERIANEX Trinational SEismic RIsk ANalysis EXpert Group
SPL sound pressure level ndashdecibels ( dB) relative 20x10-6Pascal RMS SRA seismic risk analysis
STEM scanning transmission electron microscopes TEM transmission electron microscope
USBM US Bureau of Mines USGS US Geological Survey
VEL velocity level ndash decibels (dB) relative to one micronsecond V-L L M H very-low low medium high
VS shear-wave (S-wave) velocity VP compression-wave (P-wave) velocity
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 vii
GLOSSARY Acceleration level ndash dB The level of acceleration is twenty times the common
logarithm (ie base ten) of the ratio of the acceleration amplitude to the reference acceleration amplitude
Amplitude Half the peak-to-peak amplitude associated with a seismic wave or vibration (eg displacement velocity etc) usually refers to the level or intensity of ground shaking or vibration
Average annual value The amount of damage per causative event multiplied by the annual probability of occurrence of event summed over all possible events (ie earthquakes) and all possible consequences of each event
Corner frequency The frequency of an electronic filter (iethe system) that characterizes the transition between high-frequncy energy which loses energy when flowing through the system compared to lower frequency energy passing unaltered through (bandpass) the system
Deterministic seismic hazard analysis The characterization of the hazard from a selected scenario earthquake or seismic event (DSHA)
Earthquake or event The result of slip or other discontinuous displacement (ie ldquorupturerdquo) across a geologic fault resulting in the sudden release of seismic energy Some earthquakes can be ldquoinduced or triggeredrdquo as a result of a man-made activity eg fluid injection
Enhanced Geothermal Systems (EGS) Activities undertaken to increase the permeability in a targeted subsurface volume (ie rock formations) via injecting into and withdrawing fluids from the rock formations with the intent of increasing the ability to extract energy from a subsurface heat source
Fault mechanism The description of the rupture process of an earthquake includes the forces or displacement history of the slip across the activated geologic fault
Focal mechanism A graphic representation of the faulting mechanism of an earthquake used by seismologists
Ground-borne noise Noise due to vibration of room surfaces (walls and floors)
Ground motion prediction model A relationship usually based on strong motion data (ie motion recorded near an earthquake) that predicts the amplitude of a specified or desired ground motion parameter (eg peak ground acceleration (PGA)) as a function of magnitude distance and site conditions
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 viii
Human response curves A graphic representation of human sensitivity and human response to ground vibration as a function of frequency as provided in ISO 2631 and derivative standards
Hydraulic fracturing Sometimes called ldquofracrsquoingrdquo in the oil industry and ldquofrackingrdquo in the news media the technique consists of injecting high-pressure fluids below the surface into a rock targeted mass through a borehole causing new fractures and displacing native fluids The fractures increase the permeability of the rock which aids in the extraction of natural gas andor crude oil
Induced seismic event A seismic event (eg an earthquake) that is induced by man-made activities such as fluid injection retention dam reservoir impoundment mining quarrying and other activities The term ldquoinducedrdquo has been used to include ldquotriggered seismic eventsrdquo and so sometimes the terms are used interchangeably See ldquotriggered seismic eventsrdquo below and Section 1 of this report
Inter-event interval The time interval between earthquake events Same as recurrence interval
Modified Mercalli Intensity (MMI) A 12-class categorization of earthquake ground shaking based on the observed effects of the event on the Earthrsquos surface humans objects of nature and man-made structures Class I is the lowest (eg no damage) and XII the highest category (ietotal destruction)
Moment magnitude (M) The preferred metric for the size or magnitude of an earthquake or seismic event based on its seismic moment Seismologists regard moment magnitude as a more accurate estimate of the size of an earthquake than earlier scales such as Richter local magnitude Moment magnitude and Richter local magnitude are roughly equivalent at magnitudes less than M70
Peak ground acceleration (PGA) The maximum instantaneous absolute value of the acceleration of the ground
Peak ground velocity (PGV) The maximum instantaneous absolute value of the velocity of the ground
Peak particle velocity (PPV) The maximum instantaneous absolute value of the velocity of an object or surface
Poisson process A stochastic process where the occurrence of an event has no effect on the probability of an occurrence of any earlier or later event (ie all events are random and independent of each other
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 ix
Probabilistic seismic hazard analysis (PSHA) The probabilistic estimation of the ground motions that
are expected to occur or be exceeded given a specified annual frequency or return period of events
Probability of exceedance The probability that the value of a specified parameter is equaled or exceeded within a given time period In the PSHA it is interpreted as the frequency of exceedance
Quad A unit of energy equal to 1015
Joule = 29307 Terrawatt-hours BTU = 1055 x 1018
Rate of occurrence Number of events per unit of time Usually expressed as the annual rate of occurrence (unitsyear)
Recurrence interval The average earthquakes
time period between individual
Return period It is the inverse of the annual probability of exceedanceCommonly used in place of the annual probability ofexceedance
Rock permeability The measure of transmissivity of fluids (oil water natural gas etc) through a rock mass
rms vibration The square root of the integral of the square of the vibration amplitude with respect to time divided by the integration time The root-mean-square vibration is often measured over a period of one second for transient phenomena such as short-period seismic motion The integration time must be indicated for nonstationary events The vibration may be displacement velocity or acceleration units but the units must be indicated
Scenario earthquake A projected earthquake that is constructed purposes of defining a set of actions
for the
Seismic hazard curve The result of a probabilistic seismic hazard analysis The probabilistic hazard is expressed as the relationship between some ground motion parameter (eg PGA) and annual exceedance probability (frequency) or its inverse the return period
Seismic hazard The effect of an earthquake that can result in loss or damage Examples include ground shaking liquefaction landslides and tsunamis
Seismic moment The seismic moment Mo is the product of the shear modulus of the rock material the area of slip and the (average) displacement discontinuity across the slip
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 x
Seismic risk Shear-wave velocity profile
Slip rate
Sound pressure level-dB
Spectral frequency
Structural damage
Tectonic stresses
Temperature gradient
Thermal contraction
Threshold Damage
area The relationship between moment magnitude M and moment Mo can vary from site to site but one accepted relation is M = (23)Log10[Mo(dyne-cm)] -107
The probability of loss or damage due to seismicity The relationship between the shear-wave velocity and depth in the Earth Shear-wave velocities of the material in the top few kilometers of the Earth control the amplification of incoming seismic waves resulting in frequency-dependent increases or decreases in the amplitudes of ground shaking The speed of slip across a fault in an earthquake Specifically the fault displacement divided by the time period in which the displacement occurred
The sound pressure level is equal to 20 times the common logarithm of the root-mean-square sound pressure p divided by the reference sound pressure of 20x10-6 Pa The sound pressure level is abbreviated as SPL Mathematically SPL = 20 Log10 (p(Pa) 20x10-6
Pa) in dB
The range of frequencies that constitute the ground motion record Knowledge of both the energy distribution spanning these frequencies and how their arrivals are timed is the necessary data for the reconstruction of the full record (ie full waveform of the recorded signal) in the time domain The time domain arrival rate is called ldquophasingrdquo in the frequency domain
Serious weakening or distortion of structure resulting in large open cracks in walls and masonry and buckled walls The stresses in the earth due to natural (ie geologic) processes such as movement of the tectonic plates The change in temperature with depth in the Earth The temperature gradient is a dimensional quantity expressed in degrees (on a particular temperature scale) per unit length (eg ordmCkm) The contracting of a material when in contact with something of a cooler temperature For example the contracting hot rock when subjected with cool fluids
Cosmetic damage involving cracks that do not remain open after vibration
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 xi
Minor Damage
Major Damage
Tomography
Transient ground vibration
Triggered seismic event
Vibration
Vibration exposure
Vibration level
Broken windows dislodged articles on shelves broken glass and dishes
Large open cracks structural damage due to shifting or settlement of foundation warping of walls and floors loss of structural integrity Imaging of a solid body divided into sections and characterizing a property of each section by the quality of waves passing through the section A device used in tomography is called a tomograph while the image produced is a tomogram Examples include X-Ray tomography acoustic tomography and CAT Scans Temporarily sustained ground vibration usually occurring over a time period of less than a few seconds A seismic event that is the result of failure along a pre-existing zone of weakness (eg a fault) that is critically stressed and fails by a stress perturbation from natural or man-made activity See Foreword The dynamic and repetitive motion of an object or part of an object characterized by direction and amplitude The vibration exposure is the integral (ie the sum) of the square of the vibration amplitude integrated over time in seconds The vibration exposure is measured over the entire duration of a seismic event Duration is the seismic motion discernable above the ambient motion The exposure duration is typically 2 to 5 seconds for small magnitude seismic events The vibration may be displacement velocity or acceleration but the unit must be specified
The level of vibration in decibels (dB) is 20 times the common logarithm (ie base ten) of the ratio of the vibration amplitude and reference amplitude The vibration amplitude may be the peak vibration amplitude but is typically the root-mean-square amplitude The unit must be indicated such as ldquovibration velocity level in dB relative to 1micro-insecrdquo Common reference amplitudes are
Acceleration One millionth of earthrsquos gravitation acceleration or 10-6g One millionth of one meter per second squared or 10-6msec2
Velocity
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 xii
One millionth of one meter per second or 10-6msec One millionths of one centimeter per second or 10-8msec One millionth of one inch per second or 10-6insec
Displacement One millionth of one meter or one micron
Vulnerability function A function that characterizes potential damage as a mathematical relation that gives the level of consequence (damage nuisance economic losses) as a function of the level of the ground-motion at a location
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 xiii
UNITS cmsec2 acceleration in centimeters per second per second cmsec velocity in centimeters per second
dB decibel dBA A-Weighted Sound Level ndash decibels relative to 20x10-6 Pascal
dBC C-Weighted Sound Level ndash decibels relative to 20x10-6 Pascal g acceleration of earth gravity (1g = 981 cmsec2)
GHz gigaHertz GWh giga Watt-hour
Hz frequency in Hertz or one cycle per second insec velocity inches per second
km kilometer 103 meters m meter
msec velocity in meter per second Mhz megahertz 106 Hertz
micro-insec velocity in 1 micro-inchsec = 10-6 insec micronsec velocity in 1 micronsec = 10-6 msec
mm millimeter 10-3 m mmsec velocity in millimeter per second
MW mega-Watt 106 Watts Pa Pascal 1Nm2 = 145x10-4 psi
psi pound per square inch sec second
VdB Velocity level ndash decibels relative to 1x10-6 insec
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 xiv
FOREWORD Geothermal energy is a viable form of alternative energy that is expected to grow significantly in the near and long term This is especially true if the energy from geothermal systems can be enhanced ie enhanced geothermal systems (EGS) As with the development of any new technology however some aspects are acceptable and others need clarification and study
One of the main issues often associated with subsurface fluid injection an integral part of all the EGS technologies is the impact and the utility of microseismicity (microearthquakes) that often occur during fluid injections Recent publicity surrounding injection-induced seismicity at several geothermal sites points out the need to address and mitigate potential problems that induced seismicity may cause (Majer et al 2007) Therefore it is critical that the policy makers and the general community be assured that geothermal technologies relying on fluid injections will be engineered to minimize induced seismicity risks to acceptable levels This will ensure that the resource is safe and cost-effective
Addressing the impacts and the utility of induced seismicity the US Department of Energy (DOE) in 2004 initiated and participated in an international activity to develop a Protocol to address both technical and public acceptance issues surrounding EGS-induced seismicity This resulted in an International Energy Agency (IEA) Protocol (Majer et al 2009) followed by an updated Protocol in 2012 (Majer et al 2012) These Protocols serve as general guidelines for the public regulators and geothermal operators In comparison this document provides a set of general guidelines that detail useful steps that geothermal project proponents could take to deal with induced seismicity issues The procedures are NOT a prescription but instead suggest an approach to engage public officials industry regulators and the public to facilitate the approval process helping to avoid project delays and promoting safety
Although the Protocols are being used and followed by a number of geothermal stakeholders DOE felt another document a ldquoBest Practicesrdquo document was needed by the geothermal operators This document is the ldquoBest Practicesrdquo document and provides more detail than the Protocols while still following the seven main steps in the updated Protocol (Majer et al 2012) Like the Protocol this Best Practices document is intended to be a living document it is intended to supplement the existing IEA Protocol and the new DOE Protocol As practically as possible this document is up-to-date with state-of-the-art knowledge and practices both technical and non-technical
As methods experience knowledge and regulations change so will this document We recognize that ldquoone sizerdquo does not fit all geothermal projects and not everything presented herein should be required for every EGS project Local conditions will call for different actions Variations will result from factors including the population density around the project past seismicity in the region the size of the project the depth and volume of injection and its relation to the geologic setting (eg faults) etc
This document was prepared at the direction of the DOErsquos Geothermal Technologies Program It is intended to help industry identify important issues and parameters that may be necessary for the evaluation and mitigation of adverse effects of induced seismicity and aiding in the utilization of the seismicity to optimize EGS reservoir performance We note that determining site-specific criteria for any particular project is beyond the scope of this document it is the obligation of project developers to meet any and all federal state or local regulations
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 xv
Finally induced seismicity has historically occurred in many different energy and industrial applications (eg retention dam reservoir impoundment mining construction waste fluid disposal oil and gas production etc) Although projects have been stopped because of induced seismicity issues proper study and engineering controls have always been applied to enable the safe and economic implementation of these technologies and to optimize either extraction or injection of fluids into the earth
As described in the updated Protocol (Majer et al 2012) the seven basic steps are Step 1 Preliminary Screening Evaluation
Step 2 Outreach and Communications Step 3 Criteria For Damage Vibration and Noise
Step 4 Collection of Seismicity Data Step 5 Hazard Evaluation of Natural and Induced Seismic Events
Step 6 Risk Informed Decision Analysis and Tools for Design and Operation of EGS Step 7 Risk-Based Mitigation Plan
These steps are described in detail in the following sections Each of the following sections addresses these steps individually and in order
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 xvi
1 Section 1 ONE Step 1 Preliminary Screening Evaluation
SECTION ONE Step 1 Preliminary Screening Evaluation
11 PURPOSE The goal of a preliminary screening evaluation is to evaluate the relative merit of candidate EGS site locations without investing substantial amounts of time effort and money This section describes this approach a screening evaluation based on simple analytical methods and acceptability criteria (see Section 3) One aspect of this screening is to determine if a candidate EGS site presents any problems that could impede its licensing or its acceptance by local institutions or community
When considering several candidate sites the purpose of this step is to perform a ranking and pre-selection The Protocol (Majer et al 2012) recommends a simple approach that calls for evaluating the worthiness of a candidate EGS site and when several sites are considered to compare the relative merit of each based on a bounding estimation of the seismic risk associated with the planned EGS operation
12 GUIDING PRINCIPLES FOR SITE SCREENING Many factors influence the type and location of energy projects including EGS projects Choosing sites for energy projects (and other large infrastructure projects) has been a subject of formal studies since the early 1970rsquos Lesbirel and Shaw (2000) summarize the evolution of methods used to select the sites for major projects
bull Early 1970s Least Cost Analysis
bull Late 1970s to 1980s Decide Announce and Defend (DAD)
bull Late 1980s to 1990s Development of a more comprehensive framework for managing conflicts and the emergence of comparative studies of various project alternatives
Building on this Davy (1997) noted that through the 1980rsquos the common procedure in siting facilities focused on four criteria
1 Profitability (facility under consideration must yield a benefit to the operator regardless of its status as private or public)
2 Functionality (the development of a facility must consider all technical aspects to ensure a functional operation)
3 Safety (the development must avoid all harm risks and other adverse effects to human health and environment)
4 Legality (the facility must meet legal standards) This approach presupposes that profitable functional safe and legal facilities should be built While the above criteria are important they will not necessarily have much of a relationship to the degree of public support Therefore the criteria need to be broadened to encompass the issues that are important to the community and other non-project stakeholders Since the 1990s there has been a significant body of work about gaining public acceptance of projects The work of experts such as Kunreuther et al (1993) and Raab and Susskind (2009) have made significant contributions to understanding the relationship between public opinion
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 1-1
SECTION ONE Step 1 Preliminary Screening Evaluation
and the success or failure of a project These experts and others laid the groundwork for dialogue in selecting sites for infrastructure projects (including power plants and transmission lines)
The general tendency for siting critical or controversial facilities is developing a realistic risk profile and ensuring that all the stakeholders including local communities are well informed and understand what is at stake Section 13 lays down the framework using risk evaluation for comparing candidate sites It describes how to assess the negative aspects of risk (safety possible damages nuisance) and it recommends how to present those results along with benefits to the stakeholders
13 EVALUATE RISKS WITH SIMPLE BOUNDING METHODS The screening evaluation in Step 1 is not meant to provide a definitive estimate of risk It is meant to identify the sites that would most likely be inappropriate based on risk of exceeding acceptability criteria of ground shaking This criteria is developed from experience in other sites with similar issues (see Section 3) It is intended to avoid extensive studies of sites that would have very low likelihood of gaining acceptance Therefore the emphasis on using simple bounding methods is to minimize the work before final site selection It is based on using onset of damage and nuisance criteria to define risk acceptability rather than full fledged vulnerability functions (see Section 6) to calculate risk
No method or process is generally endorsed to achieve the goals in this step but common sense and recent projects not all specifically for EGS can give useful insights For example studies performed by US Department of EnergyNational Energy Technology Laboratory (DOENETL) for the carbon capture and sequestration (CCS) projects can be used for site screening (DOENETL 2010 Screenings are often not formally risk based The present Best Practices document emphasizes the use of risk information to help make decisions It assumes that a technical screening based on the geology and other physical considerations has already been done
The process recommended in Step 1 is summarized in Figure 1-1 and starts with examining local regulations In this process each of the separate risk quantification parts can be simple but must convey reasonable confidence in the bounding results or complete and high resolution knowing that once the screening is done and the site selected a detailed risk analysis will be performed (Step 6 of the Protocol Majer et al 2012)
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 1-2
SECTION ONE Step 1 Preliminary Screening Evaluation
Source NETL 2009
Figure 1-1 Elements of a Bounding Risk Analysis
131 Local State and Federal Governmentsrsquo Acceptance Criteria As part of project definition developers should establish criteria to quantify and rank potential EGS areas using acceptance criteria including criteria of the type described in Section 3 of this document The criteria should also include primary factors leading to a gono-go decisions and factors that may lead to a contingent set of analyses For exampleprimary factors might include
bull Verifying that the site can be permitted under federal state and local regulations including zoning regulations
bull For projects with federal funding assuring National Environmental Policy Act (NEPA) requirements can be met
bull Verifying that mechanisms can be established for obtaining access from surface and subsurface owners for storage surface facilities and pipelines
132 Impact on Local Community There should be a complete list of possible impacts on the local community For the social impact and nuisance this list should be completed concurrently with the outreach program (see Section 2) to permit the development of simple consequence metrics These metric will be used in the bounding risk analysis with classification of very-low (V-L) low (L) medium (M) or high (H) consequence as suggested in the Protocol (Majer et al 2012)
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 1-3
SECTION ONE Step 1 Preliminary Screening Evaluation
133 Natural Seismicity and Associated Long-Term Seismic Risk Step 1 is not intended to require extensive calculations and comprehensive research field work efforts or development of extensive databases on seismicity or vulnerability of buildings Risk from natural seismicity can be estimated by available techniques and software using methods reliable enough to give orders of magnitude We recommend using seismicity data ground motion recordings and updating or installing a local network as soon as possible (see Section 4) An estimate of probabilistic seismic hazard can be taken from existing hazard maps (see for example US Geologic Survey [USGS 2008]) However adjustments should be made to include natural seismic events as small as moment magnitude M 4 or M 35 if possible This will create a base-line that can differentiate natural risk from risk induced by the EGS where earthquakes are typically smaller than M 35 The updating effort should cover local seismic source zones or faults and ground motion prediction models for small distances and very small magnitudes Given the complexity of the induced earthquake generation we recommend performing this update using case studies of other similar EGS projects Current efforts to physically model small earthquakes in the areas of crustal stress disturbance are still in research mode they are very complex and require extensive calculations ndash not what is envisioned here
Whenever possible site-specific ground motion that takes into account the local characteristics and geology should be included within the scope and level of effort commensurate with the level envisioned for this section In most cases building-code (see FEMA 232 [FEMA 2006] and FEMA P-749 FEMA [2010]) approaches and data bases can be used
Risk of physical damage economic loss estimate and loss of life need only be estimated using standard methods with existing data bases either generic or with analogs
Long-term risk is usually expressed in terms of monetary loss and loss of lives and the goal is only to be able to determine whether the risk is V-L L M or H (see definition of risk levels in the Protocol [Majer et al 2012])
134 Magnitude and Location of Worst Case Induced Earthquake and Associated Risk Earthquakes induced in EGS fields are generally in a magnitude ranging Mlt -2 (insignificant) to about M 35 (locally feelable) (Majer et al 2007) Somewhat larger earthquakes have been observed but very infrequently The largest earthquake to date believed to be associated with an EGS operation is M 47 However note that every site will be different depending on whether there are pre-existing faults within the EGS field which implies a very good knowledge of the subsurface geology and therefore may not be applicable at this stage (ie in the screening Step 1) If enough information is available to perform a simple analysis the case of the Basel Switzerland EGS study can be used as an example of best practice (SERIANEX 2009) In the SERIANEX study it is believed that all faults within 15 km of the injection were identified and characterized to determine the maximum possible earthquake These calculations included fault geometry orientation and the best-estimates for the orientations and directions of crustal stresses Assuming an earthquake could be triggered by changes in rock properties the largest modeled event was retained as the maximum possible magnitude that could be induced by the EGS By necessity this magnitude will always be small since the existence of a large fault capable of being stimulated to generate very large earthquakes should automatically disqualify a site from EGS development
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 1-4
SECTION ONE Step 1 Preliminary Screening Evaluation
135 Assessing the Overall Risk of the Planned EGS Because of its approximate and bounding nature the metric of risk estimates as suggested in the Protocol for Step 1 is expressed on a scale of four values V-L L M and H These have to be interpreted as levels of failing to fulfill needs and regulations and failing to obtain acceptance from the community That is a V-L risk signifies that the project is practically without risk and is a ldquogordquo The likelihood of passing all hurdles is very high On the opposite end of the risk spectrum is the H risk estimate a ldquono-gordquo indicator Here there is too much uncertainty in fulfilling regulations or acceptance criteria or there is a high likelihood that opposition to the project will force abandonment Note that only risks in the form of negative consequences (physical damage nuisance) need to be considered Benefits resulting from EGS operations do not need to be formally considered in this step This provides a level of conservatism in the pre-selection We note that one can introduce benefit parameters to differentiate between close candidate sites Rather than expressing risk on a scale of 1 to 4 (V-L L M and H) it is recommended to translate the estimate into a qualitative description of the expected effects This would better communicate the risk and facilitate interaction with local communities and populations
Short of performing a detailed risk analysis (Step 6) once a site has been selected the overall risk of the planned EGS should include
bull The baseline risk from natural seismicity in standard metrics (physical damage monetary terms loss of lives)
bull An estimate of the added risk from EGS as a function of time correlated with the planned injection program This estimate should be for small earthquakes that would potentially occur in the volume occupied by the geothermal field The estimate should be expressed in relative terms at the four levels V-L L M and H
bull An estimate of the added risk also correlated with injection for earthquakes that could be triggered on nearby existing faults (V-L L M and H) using maximum possible magnitude(s) and location(s) of triggered earthquakes
bull A rough estimate of areas where the impact of the induced seismicity would be highest and which groups of the population would most likely be affected This would include an upper-bound on the possible effects
136 Identify Main Possible Risk-Associated Reasons for Not Completing a Project Some of the possibilities for not completing a project are
bull Technical The geology and general characteristics of the planned EGS field do not comply with acceptable physical criteria This analysis is performed in the first phase of the site selection
bull Regulations Regulations and local ordinances can limit or forbid certain types of operations For example there are limitations on hydraulic fracturing exist in some areas
bull Lack of Acceptance State or local communities may have ordinances or vote in ordinances similar to hydraulic fracturing of the previous item
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 1-5
SECTION ONE Step 1 Preliminary Screening Evaluation
bull Financial Infeasibility This can be due to the characteristics of the EGS field or can be compounded by additional expenses for mitigation of the expected induced risk
bull Abandonment The project can be abandoned by the developer for various reasons including company strategic re-directions bankruptcy etc
The overall risk analysis in Step 1 should rank the possible scenarios of non-completion This should include relative ranking for each alternative and propose possible mitigation alternatives
14 EGS PROJECT BENEFITS For the purpose of helping - decision-makers and local communities evaluate a project pragmatically there should be an identification and assessment of possible benefits of completing the EGS projectThese could possibly include
bull Ecological maintenance and protection of the environment on the EGS site
bull Provisions for new roads and general local infrastructure
bull Benefits to the developer including financial improved strategic alignment
bull Financial benefits to local communities through negotiated electricity prices
bull Social benefits including increased employment in the region Identifying and clearly characterizing and documenting possible benefits are necessary to provide meaningful information to the stakeholdersrsquo decision making
15 DOCUMENTATION FOR THE PROJECTrsquoS INITIAL PHASE DECISION MAKING
151 Full Technical Documentation Detailed documentation of the processes and analyses should be transparent complete and accessible The documentation should describe all assumptions used in the analyses a clear description of the methods of analysis and a full accounting of data bases Simplicity and approximate bounding methods should be carefully documented to give confidence that the approaches are rigorous rational and provide some level of conservatism in spite of their simplicity The completeness and appropriateness of the documentation should clearly efficiently and convincingly support the decisions
152 Summary Evaluation of the Risk To inform all stakeholders including non-experts and the general public the documentation should contain a summary evaluation of the information that led to the decisions This shoule include all of the following
bull A summary of the dominant risk issues
bull A summary of benefits
bull A description of mitigation measures and a plan to address risk issues
bull An explanation of the decision to pursue or not pursue the project
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 1-6
SECTION ONE Step 1 Preliminary Screening Evaluation
bull Finally if a decision to pursue a plan for completing the project
16 CASE STUDIES Substantial projects are usually the subject of a feasibility analysis prior to making the decision to proceed However there are no documented cases to date that followed a process such as the one advocated in Step 1 Most of the time decisions on whether or not to proceed have been ad hoc They have not been based on a rigorous screening processor lack the level of communication accessible to all stakeholders In some cases risk analyses have been performed that pertain to Step 6 of the Protocol and are usually full detailed analyses rather than the simple or bounding type of approach advocated in this step
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 1-7
2 Section 2 TWO Step 2 Outreach and Communications
SECTION TWO Step 2 Outreach and Communications
21 PURPOSE Since stakeholder acceptability is an important component of an EGS project outreach and communication become important elements of the project Poor communication and outreach can ldquomakerdquo ldquobreakrdquo or seriously delay a project (Majer et al 2007) Since all EGS projects in the US require environmental permits that address a variety of safety and environmental issues (air quality water traffic etc) and induced seismicity it is critical to keep public stakeholders informed as part of the permitting process For later reference it is also critical for project operators to consider and act upon public stakeholdersrsquo input as the project proceeds The outreach and communication program should facilitate communication and maintain positive relationships with the local community the regulators and the public safety officials All are likely to provide feedback to the geothermal developer at different times during the project
Since to date few EGS projects have been implemented we cite principles and examples from other similar types of projects to provide a context for EGS outreach and communications Much of this comes from publications about siting of industrial facilities including several energy projects and their outreach and communication approaches Experiences from two different EGS projects are also cited one near a population center and one far from any population center Also some of the referenced non-EGS projects deal with hazards different from induced seismicity and by comparison have higher overall risk potential Nevertheless valuable lessons can be learned from these examples and incorporated into the outreach and communication program for an EGS project As with all steps outlined in this document the effort expended on this step can vary significantly For example if the EGS project is far away from any assets of concern (eg areas with dense population critical facilities or particular environmental sensitivities) then much less effort will be required compared to a project that is close to many assets andor under more stringent regulatory control
22 MAIN ELEMENTS The EGS outreach and communication program should help the project achieve transparency and participation based on the following suggested framework
bull To develop the most effective outreach and communications program the project developer should make an initial assessment of the level of induced seismic risk to nearby communities (see Sections 3 and 4) and the level of community awareness and concern
bull At the start of the project the project developer should make an outreach plan and periodically update the plan as the project proceeds This includes modifying the plan as needed to address stakeholder concerns
bull The amount and type of outreach should be specific to the project situation including distance from population size of the project duration of activities with potential for induced seismicity the regulatory environment and the number and types of entities responsible for public safety
bull The dialogue should be open informative multi-directional and invite enquiries
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-1
SECTION TWO Step 2 Outreach and Communications
bull As the project progresses and more information is obtained meetings should be held periodically
bull The stakeholder groups (eg community regulators public officials etc) should be approached at their appropriate technical levels and a mechanism to respond to their concerns and questions should be put in place and maintained throughout the project
It must must be recognized that there could be many participants in the outreach and communications plan including the project proponents (eg developer team seismologist(s) civil or structural engineer(s) local utility company and representative(s) of the funding entity) the community (eg local project employees community leaders and at-large community members) and public safety officials regulators andor organizations (eg law enforcement fire department emergency medical personnel)
23 EXAMPLES In this section we summarize experiences related to siting industrial facilities and energy projects to suggest some guiding principles for an EGS outreach and communications program
Few examples exist of outreach and programs associated directly with geothermal projects so this section begins with two examples of outreach programs from other industries Also included are summaries of the outreach activities from two EGS projects one near a population center and the otherfar from any population These two geothermal projects can be viewed as possible end-members of effort that may be required for EGS projects
231 Other Industrial Projects Relevant information and experiences from two different waste disposal projects are summarized below It is not implied here however that EGS-induced seismicity has the same risk potential as those hazards associated with waste disposal (we know of no case of structural damage associated with induced seismicity from an EGS site let alone any lethal hazards) Both projects developed community outreach and communication programs (Community Relations Plans) It must be noted that the overall project scopes of these two energy applications are much larger than most EGS projects thus financial resources are much larger in these types of projects and more resources were used on outreach than would be expected in a typical EGS project Both plans were aimed at interested stakeholders including individuals organizations special interest groups governmental agencies tribal governments and tribal members The purpose was to provide information and facilitate participation in the permitting process related to waste disposal and other activities at the sites Before the implementation of the Community Relations Plans (the ldquoPlansrdquo) there was a significant outreach effort to establish open working relationships and the Plans provided a vehicle to expand public participation in the dialogue Overall the Plans addressed six objectives related to outreach and communications
bull Establishing working relationships with communities and interested members of the public
bull Establishing productive relations between the operator and affected local groups including the participation of government agencies regulators
bull Informing communities and interested parties of permit activities
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-2
SECTION TWO Step 2 Outreach and Communications
bull Minimizing disputes and resolving differences with communities and interested members of the public
bull Providing timely responses to individual requests for information
bull Establishing mechanisms for communities and interested members of the public to provide feedback and input
In one case a web page was developed to provide information on permits permit-related activities and meetings (including the Permit itself as well as other pertinent documents relating to the operation of the project) and featured a well-received comment and response tool for the public The Plans also specified that notices about activities at the site andor the Permit were to be published in local newspapers and that the local regulatory agency would maintain a mailing list of interested parties to receive notices about the project An e-mail notification service was implemented as well
In essence the Plans formalized a significant amount of outreach aimed at local governments civic organizations schools and anyone interested in learning about the project A key tenet of the outreach programs was to ldquoeducate on the facts and avoid the need to correct the rumorsrdquo As noted in the preceding section openness and transparency have been found to be the most effective ways for the various stakeholders to understand the project thus enabling the project to gain public acceptance
Operators approached the issue of public acceptance by following a hierarchical approach 1 Discuss the project with elected officials to gauge their interest in having the project
within their jurisdiction(s) 2 Make presentations to the local officials (in this case the Chamber of Commerce) which
included many community business leaders to generate interest in the project 3 Engage with various civic organizations to educate the members of these organizations
and show them the site Education programs and site visits were repeated periodically as the projects progressed enabling the new stakeholders to be informed The operators took a proactive approach toward information dissemination by requesting invitations to public meetings so they would be included on the agenda Although they participated in many such meetings in the early stages of the projects at present they meet with local organizations on an annual basis The operators began building public support by providing information to the community and making a management-level commitment to answer all questions that were asked even about sensitive issues that might have ldquopainfulrdquo answers The operators accepted that attempting to hide information would be detrimental overall because if the community were to discover the facts on their own the credibility of the project proponents would be undermined Furthermore by providing the data the operators could ensure that the facts were correct Today these projects are highly supported by the community to the point where attendance at public meetings has gradually declined as members of the community have grown more comfortable with time At the start of one project the local economy was in trouble with many in the community unemployed (an ongoing concern worldwide) However the desire for jobs did not outweigh the concerns about the safety risks associated with the project The project managers considered
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-3
SECTION TWO Step 2 Outreach and Communications
what they could offer to the public beyond employment and realized that they could offer the following
bull Provide expertise that was previously unavailable (ie provide an in-kind service to the local city for assistance with issues that involve advanced engineering andor scientific expertise)
bull Make donations to local organizations including the donation of computer equipment to schools
bull Purchase specialized equipment for school education programs or other specific local needs
bull Through an MOU with the City provide training to emergency personnel and support the Cityrsquos emergency facilities Specifically this included the training of local emergency and hospital personnel and dispatching local Emergency Medical Technicians (EMTs) to accident sites
bull Get engineers and scientists more involved in the community by volunteering to teach at the local Community College and public schools (enabling students to learn from highly skilled PhDs who graduated from top-tier academic institutions)
bull Participate in community events like the National Environmental Week bull Provide an information and visitor center with a video tour of the facility display boards
and other information and have management actively encourage the public to come and talk to them at the Information Center
Another plan to develop a Carbon Capture and Storage (CCS) project within depleted gas fields provides a useful case history ndash particularly in terms of the timing and type of communications between the project stakeholders and the local community ndash on what activities could have been avoided to maintain mutual trust between all parties and the project Some valuable lessons were learned and can be used as guidelines for EGS projects It is also worthwhile to mention some factors to avoid in these activities
bull The project was presented to the community as a final plan therefore stakeholder input was not obtained or addressed before the plan was finalized
bull Even at the initial phase no open dialogue existed between the project developer and the appropriate governmentregulator agency This led to a situation in which the project was presented and interpreted as a project of the developer alone instead of a project that was mutually beneficial to different stakeholders This made the developer an easy target for opposition
bull After local opposition became clear a dialogue between stakeholders was set up via an ldquoadministrative consultation grouprdquo (government consultant) however the dialogue was limited only to government entities The project developer non-governmental organizations research institutes and community groups were not involved Although the consultation group did improve communication between the different levels of government it did not bring the viewpoints of the members closer to each other or decrease local opposition to the project
bull The debate between the stakeholders took place mostly in public via formal procedures organized events press releases or through the media Little informal andor direct contact occurred between the project developers and opponents This made the situation
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-4
SECTION TWO Step 2 Outreach and Communications
worse Direct contact should have been established at the beginning when stakeholders had not already taken their positions This could have been achieved using a neutral facilitator to build mutual trust and openness The needs and values of the community could then have been taken into account in planning and implementing the project Although implementation of the project might not be consistent with the wishes of all stakeholders the fact that they had been involved in an open fair and transparent process in which stakeholders trusted each other would limit resistance to the project
bull Through various institutional procedures the national government gradually withdrew executive decision-making abilities from the municipal government These changes in procedures (which were often not announced to the municipality in advance) increased the distrust in the national government by the local stakeholders and increased their opposition to the project Had these changes in procedures been discussed openly with the local stakeholders (especially with the municipal government) in advance a more unified approach would have been taken probably leading to a less negative tenor of the debate
bull Absent an understanding of national and international energy policy (ie CCS climate change energy security etc) the public had difficulties understanding why the project was required at all and why their community had been chosen More attention to contextual aspects and the involvement of the national government might have led the public to interpret the project differently and accept it more readily
bull The initial presentation of the project was considered to be too technical and too complicated for the public to understand raising many questions A better adaptation of the presentation to the demands and needs of the public was required Underestimating the intelligence of the local community can have similar consequences the abundance and accessibility of information via the internet provides a powerful tool for information to the public
bull Because the project developer and government agency were both invested in the project they were not considered to be suppliers of trustworthy information The lack of openness and transparency from the beginning contributed strongly to this sentiment If the project developers had shared with the public the underlying reasons for the project and the associated technical challenges and uncertainties more trust would have developed
bull Opponents and proponents of the project both communicated to the residents each providing their own (and sometimes inconsistent) information Almost no communal communication efforts occurred in which opponents and proponents cooperated with each other or simply sat down at the same table This lack of communal communication increased the idea that members of the public had to choose sides making a ldquoblack or whiterdquo type of decision More nuanced viewpoints were never heard
This experience shows how a lack of outreach and communication could lead to opposition to a project This could lead to increased opposition with time leading to an impasse that would leave little room for open dialogue
Therefore here are some useful lessons to be taken from these cases
bull Community and local stakeholders should be involved early in the project process to create mutual trust and commitment to the project
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-5
SECTION TWO Step 2 Outreach and Communications
bull The values needs and opinions of stakeholders and the community should be taken into account in discussing possible project designs There should be room for adaptation leading to acceptable compromises in the project design
bull Regular formal and informal contact should take place during project implementation and operation
bull Discussion should move beyond the proposed project to include the relevant policies and context and how the project serves to meet the broader societal goals
232 EGS Projects The examples given above are not specific to EGS and it would be surprising if such efforts were required for gaining project acceptance (both regulatory and public acceptance) as in the two examples above To illustrate this point we give two examples of successful community outreach for two ongoing EGS projects one with high seismicity near a somewhat cautious community that had experience with induced seismicity and another one with low seismicity somewhat distant from a community that had no experience with induced seismicity This second project however was located in a tectonically active geologic province where residents have experienced natural seismicity It should be noted that other EGS projects are in the process of obtaining final approval for operations but because they have not advanced to the stimulation phase they cannot be considered as ldquobest practicesrdquo yet Currently no US examples illustrate the process starting from ldquoscratchrdquo (ie no geothermal production at all) but these two examples will cover the range of activities
233 Project near a Community As EGS becomes more successful there will be cases where EGS projects may be located near communities where small levels of induced seismicity may be perceived either as an annoyance nuisance or even damaging In these cases more outreach education and communication will probably be needed when compared to more isolated projects In the case described here the particular subject project was an existing geothermal field The developer wanted to augment the production from the hydrothermal system with an EGS project In addition there was already a history of injectionproduction-related seismicity for over 30 years In one way this was beneficial because the operators residents and regulators had experience with seismicity issues In other ways this was detrimental Some residents were wary because it was perceived that the EGS project may increase felt seismicity above the current levels of seismicity (which are still not acceptable to some residents see mitigation Section 7)
It should be noted that in the early days of the hydrothermal operations the previous owners of the project were not the model of community outreach and even denied that the seismicity was induced by the geothermal operations but it was natural and would occur anyway (this added to the effort required for community acceptance in later years) As time went on and the USGS continued its earthquake monitoring direct correlations could be made between injection and seismicity the owners realized that it was to their benefit to change their stance on the causes of the seismicity and started an improved community outreach program Over the years as ownership changed the outreach and communication program has greatly improved
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-6
SECTION TWO Step 2 Outreach and Communications
While there is still some degree of community concern and opposition regulators and policy makers have accepted the project and allowed operations to continue It is doubtful that this would have happened without an effective outreach and education program The existing (pre-EGS) outreach education and community relations consisted of the following elements
1 Open access and communication with all stake holders on a routine basis
2 Up-to-date information on various aspects of the project (regular community newsletters) 3 Sensitivity to community concerns (special meeting arranged if necessary)
4 Periodic meetings with all stakeholders 5 A public visitor center with up-to-date information about all aspects of the geothermal
project with a section for EGS 6 A public hotline that can be called for any concerns
7 Third party monitoring of seismicity for unbiased results (the USGS and other institutions had been monitoring for many years as part of the USGS earthquake hazards program and various research efforts) All of these data were publically available
8 Funds contributed to community needs (see mitigation section of this document Section 7)
Additional efforts that were implemented as part of the EGS-specific phase of the project are outlined below As can be seen prior to the EGS project there was already a considerable outreach program in place However once the EGS project was undertaken the residents expressed additional concerns regarding different injection procedures and possible generation of increased induced seismicity over current levels This required further education and outreach for both the regulators and the community
These outreach activities were based on the above principles but the education and community outreach were focused on the perceived impacts from the EGS project itself instead of educating the community and regulators about the aspects of the project that were designed to limit the induced seismicity as described below
1 It was in the best interest of the project to control the seismicity rather than maximize the seismicity (ie some community members having limited information about EGS assumed that the operators wanted to maximize the seismicity believing that the larger the fractures the better) Once the community was shown that the best case for the operator was many small fractures rather than a few large fractures the community was more at ease with the project
2 The EGS project was in the part of the field that was the most distant from the community thus reducing the impact of the seismicity in general
3 Injection would be done in steps such that one could monitor the seismicity as it developed and thus have better chances for control
4 Regular (monthly or more) public updates would be providedabout the seismicity and project aspects to the public
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-7
SECTION TWO Step 2 Outreach and Communications
5 Timely responses would be made to any inquiries to the hot-line 6 Updated visitor center would include EGS activities and education (eg ldquoWhat is EGSrdquo
FAQs etc) This project is a good example of where community education about the project (emphasizing the good practices and engineering aspects) convinced the regulators and the community that the risk of induced seismicity was minimal This was done by partnering with public institutions such as universities the USGS and similar third parties to assure the community that the project operator was following best practices In any case it is clear that a variety of outreach options are available to assure the community that the project can be in its best interest
As of this writing the subject project is approaching the six-month time frame without any induced seismicity issues Strong community outreach showing timely results and demonstrating the tangible benefits of the project to the community have allowed the project to move ahead smoothly
234 Project Distant From a Community The second project is one that is located in a rural area with the closest community approximately 25 kilometers away This community has less than a few thousand people with few if any sensitive assets (such as electronics assembly facilities or research institutes) with a rural community and small structures The closest large city is about 75 kilometers away The project is in a tectonic area that has experienced large seismicity over the last 50 plus years (M 60 plus within 50 kilometers) but the subject project is in a 25 km diameter ldquoholegaprdquo of seismicity
This is also an ongoing geothermal area that has implemented an EGS project to supplement existing production Prior to the EGS project the only regional seismic monitoring was done by the state university The detection threshold was between M 10 to 15 below any felt events at the field let alone at the community 25 kilometers away Thus there was no pre-existing community concern due to any induced seismicity during the previous 10 years of operation The community interaction consisted of the project director requesting a series of meetings with the public to inform them in an ldquoopenrdquo forum about the project itself including the potential for induced seismicity Additionally the operator requested a meeting with local officials and regulators (state and federal) At this two-hour meeting the basics of EGS were explained and the various components of the EGS project were laid out This was done as part of an overall environmental assessment for such factors as air and water qualitysupply impacts noise construction impacts and land disturbance From this meeting it was agreed that an induced seismicity protocol would be developed based on the existing IEA (Majer et al 2009)
This protocol was fairly simple with the key component being that if the seismicity due to EGS ever exceeded M= 20 the project would stop and reassess the injection parameters The public was continually informed via news media and community presentations as to the progress and nature of the project This informed and transparent approach developed a positive relationship between the operator and the public receiving interested inquiries instead of backlash after a number of seismic events were felt by the community members
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-8
SECTION TWO Step 2 Outreach and Communications
24 RECOMMENDED APPROACH The preceding discussion illustrates the four main requirements of a ldquobest practicesrdquo approach to outreach and communications about EGS projects Those four requirements and their essential components are listed below Again to re-emphasize in some cases much less effort will be required and in other cases a significant effort as previously described may be required
1 Identify key stakeholders early in the process Particularly for pilot projects that may gain significant attention it is critical to identify and engage all stakeholders early in the project lifecycle so that the outreach is properly targeted Evaluating opinions and concerns in the early stages of the project will ensure that the outreach is responsive to the stakeholder community Surveys focus groups and interactive meetings with a select group of representatives of the community can help ensure that the right participants are involved and that the right issues are being discussed
2 Establish an appropriate outreach team clearly defining the processes for both internal and external communications for the project This team will become the ldquofacerdquo of the project and thus will have a direct impact on how the community perceives the project and the project developers Important elements include the following a Understand the audience and tailor the information to match the intended audiencersquos
degree of interest education and time constraints b Adapt the format detail and complexity of the outreach to the specific needs of the
audience c Maintain consistency of messages delivered to the public particularly about real or
perceived public risks This is especially important to coordinate when the project developer is made up of several operators or agencies
d Monitor the community ldquobuzzrdquo to gauge perceptions note any relative pre-existing community issues identify misconceptions and develop strategies to counteract them
e Develop a multi-disciplinary outreach team that may include project managers scientists government officials company spokespersons safety personnel technical service providers and other personnel who are involved in key decision making processes for the project
f Set up a local office in the community ideally including technical displays for visitors (ie visitor center)
g Institute a mechanism for community feedback such as community meetings and hotlines
3 Provide the community with complete and credible information about the project necessarily including contentious issues This includes such elements as
a Providing a context for the project in the form of a national energy policy for example Having a government representative discuss the project with the community may help to gain the public trust
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-9
SECTION TWO Step 2 Outreach and Communications
b Provide appropriate and relevant data to the community this may include a website with seismicity data gathered by an independent third party
c Assembling the evidence and analyzing the options in advance demonstrating that the project is well conceived and placing any associated risk in the proper context
d Fully addressing all aspects of the project including those that may be perceived as negative and explaining the trade-offs that are made in choosing particular options
e Reaching consensus on the basic justification of the project This means demonstrating that the project provides the best solution to the problem(s) at hand
f Actively managing the outreach and communication program to ensure that requests for information are being fulfilled
g As the project advances changing the dialogue appropriately The dialogue will naturally shift from addressing concerns to sharing progress and results thus keeping the community engaged
4 Gain a community perspective as a pathway for gaining public trust A developer who has better insights into the diverse concerns of the community will be better equipped to demonstrate how the project can support the community This typically requires
a Gaining an in-depth understanding of the local situation (economy employment education energy needs environmental issues etc) to provide a context for understanding the underlying views about the project and its risks and benefits
b Providing a venue and method for the community to express their views in a way that is comfortable to them thus helping to open the lines of communication This requires a fundamental acknowledgement of public perspectives particularly about the key factors that cause people to worry about the project andor its risks and permits a proactive and constructive discussion
c Enabling ldquovigorous public debaterdquo about the pros and cons of the project and maintaining fairness in the siting process (ldquosocial justicerdquo or ldquoenvironmental justicerdquo) This may be difficult to accommodate in the EGS process as it is common to have a pre-determined location for such a project based on the ownership of the land and the ownership or leasing of mineral (geothermal) rights That is there is rarely an option for moving an entire EGS project and resource considerations may dictate a very limited set of possible well locations
d Initiating stakeholder involvement process as early as possible and setting realistic but firm timetables
e Including broad representation of legitimate stakeholder groups (including government agencies and citizen groups) and seeking consensus perhaps by using ldquoprofessional neutralsrdquo to facilitate collaborative decision-making
f Identifying community needs that could be partially or fully met by the EGS project (eg school science programs support to libraries or community facilities supplied by produced geothermal fluids such as a community greenhouse heating system swimming pool etc)
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-10
SECTION TWO Step 2 Outreach and Communications
g Conveying information about project safety including the mandates and responsibilities of the project operator and local safety officials
h Structuring the stakeholder involvement processes to supplement (but not supplant) the formal back-stop process while modifying formal processes to better accommodate consensus-building opportunities
Additional suggestions about how to approach the community are included in the Protocol (Majer et al 2012) As noted in the Protocol it is expected that the approach presented herein will be suitably modified according to the needs and nature of the project and the surrounding environment
25 SUMMARY The outreach and communication program should be designed to engage the community in a positive and open manner thus building credibility and trust The program should begin with an analysis of the concerns and needs of the community to ensure that the outreach is properly targeted A hierarchical approach (approaching elected leaders and safety officials first then safety officials and then the public) can help set the tone and scope of the dialogue The project should be presented in the larger context of national energy policy and the underlying drivers and the potential benefits to the local community providing nuance and dimension to the discussion
Outreach and communication should be undertaken before activities begin on site and should continue as operations proceed Information should be delivered proactively by the developer avoiding the need to go on the defensive As noted by examples given above an outreach program should ldquoeducate on the facts and avoid the need to correct the rumorsrdquo The developer should strive to be seen as a positive force that understands and responds to community needs and concerns and provides an overall benefit to the community By understanding the community and its needs and concerns the developer can determine creative ways to engage in a dialogue that demonstrates the benefits of the project particularly at the local scale Although it will have a strong focus on the exchange of information a successful outreach and communication program will also engender long-term support for the project It should also be reiterated that induced seismicity will not be the only need for outreach and education As stated above water issues air quality traffic noise and construction impacts will all require similar efforts (more or less) and thus induced seismicity should not be singled out as a standalone issue in fact in some cases it will be a minor issue
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 2-11
3 Section 3 THREE Step 3 Criteria for Damage Vibration and Noise
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
31 PURPOSE This section provides guidelines for selecting criteria for vibration and ground-borne noise to assess the potential impact of EGS-induced seismicity on the built environment and human activity These criteria may be used for impact assessment real-time monitoring and control or post-event assessment The criteria described below are base criteria that define thresholds of acceptability They do not address the severity of impact as a function of magnitude That is they do not provide guidelines for assessing the cost or extent of damage to structures the percentage of people ldquohighly annoyedrdquo or the level of disruption to manufacturing activities These impacts and risks are represented by a vulnerability curve as described in Section 6 where the methods of risk analysis are discussed The guidelines discussed in this section are based primarily on common practices in the mining transportation medical research and manufacturing industries and on published standards for assessing human annoyance Criteria may be developed to suit particular situations related to EGS These guidelines are intended to be simple easily understood and easily applied while addressing common standards for vibration impact assessment Even so they are perhaps unfamiliar to the EGS industry Vibration and noise control engineers are familiar with and can readily interpret these guidelines and can apply them to predicted or measured ground motion and ground-borne noise using commonly available instrumentation and analysis techniques While the magnitude and spectral character of transportation-related vibration and noise can be predicted with a modest degree of certainty EGS seismicity must necessarily be described in probabilistic terms The assessment of the acceptability of an EGS project has to be based on the probabilities of occurrence of various ground motions and an identification of an acceptable change in these probabilities relative to natural or background seismicity Requiring that EGS-induced ground motion never exceed a certain magnitude in areas where that magnitude is often exceeded by natural seismicity is unreasonable However an EGS project that increases the probability of occurrence at a given magnitude within a given time period relative to the seismic background by less than some agreed-upon percentage might be considered acceptable These probabilities can in principle be translated into cost and nuisance risk thereby aiding the selection of appropriate criteria This is necessarily a socio-economic problem and is discussed in greater detail in the context of risk analysis in Step 6 of this document Some experience has been gained with respect to building damage activity interference and human response to seismicity related to EGS projects in Europe other geothermal fields and more recently to hydraulic fracturing in the US Such experience can be combined with that of the transportation and mining industry to help develop acceptable criteria for a given project Levels or magnitudes of vibration and noise can be identified below which no impact would occur based on experience with these industries These ldquothresholdsrdquo and higher impact levels are discussed below
While an impact assessment of an EGS project may employ particular criteria the actual vibration or noise that may occur during EGS activity including any that may exceed these criteria might not actually produce an impact in the form of identifiable building damage interruption of service interference with manufacturing or interference with domestic human activity The post-EGS assessment of damage or activity interference resulting from EGS
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-1
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
activity should be based on actual damage or activity interference for which pre-EGS surveys of existing conditions and building conditions are necessary
Table 3-1 is a guide to various sub-sections of this section as a function of ground motion For example if a site would be located in proximity to a hospital or medical laboratory no concern would be expected if the expected maximum ground motion would be less than 005 mmsec RMS measured over a time period of one second Where EGS-induced ground motions in excess of 005 mmsec might be expected one should refer to Section 37 for a more detailed discussion of the effects on laboratory and manufacturing facilities If the hospital also has an MRI Section 37 should still be consulted if the projected root-mean-square vibration velocity exceeds 00063 mmsec or the projected PGV exceeds 00005 g The values shown in Table 3-1 are not criteria as these are discussed in the indicated sections Rather Table 3-1 is a guide for using this document
To the extent that EGS facilities would be located in a remote area distant from cultural features the considerations of this section might not apply However communities or structures of some type would invariably be located within a few miles of an EGS site necessitating an assessment of potential impact on them be it slight Many of the potentially impacted receivers are subjected to naturally occurring ground motions and the occasional EGS-induced ground motion may be more of a nuisance than a cause for alarm or damage
Table 3-1 Impact Guide
Impact Maximum Velocity Acceleration Section Bridges Reinforced concrete structures
125 mmsec PGV 02 g PGA 33 34
Building Damage 125 mmsec PGV 002 g PGA 32 Human Disturbance 01 mmsec RMS (1-sec)
04 mmsec PGV 000036 g RMS (1-sec) 36
Hospital laboratories wet chemistry laboratories
005 mmsec RMS (1-sec)
000018 g RMS (1-sec) 37
MRIs scanning electron micro-scopes
00063 mmsec RMS (1-sec)
00005 g PGA 37
Semiconductor manufacturing research laboratories scanning transmission electron microscopes
32 mmsec RMS (1-sec) 10 micro-g RMS (1-sec)
37
32 BUILDING DAMAGE CRITERIA Dowding (1996 pg 110) has categorized building damage into the following categories (1) threshold cracking (2) minor damage and (3) major damage A threshold cracking criterion identifies an acceptable level of ground shaking above which cosmetic damage due to cracking of stucco plaster or gypsum board walls might occur and where crack closure may be expected Minor damage involves cracking without permanent opening damage to dishes fallen objects
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-2
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
and broken windows Major damage is indicated by permanent opening of cracks due to structural damage involving weakening or deformation of the structure shifting of foundations and significant settlement as might be associated with liquefaction Major damage criteria are typically much higher than threshold damage criteria by an order of magnitude Major damage criteria are of a type that may be called consequence criteria and have a more complex representation that allows estimating the full probability of damage for a given set of ground shaking and local conditions Major damage criteria are of a type that may be used to develop the vulnerability functions that are used in standard methods of detailed risk analysis (see Step 6) The various building damage categories are discussed in greater detail below with particular emphasis on threshold cracking criteria as these are likely to be most relevant for EGS-induced seismicity Moreover meeting threshold cracking criteria would imply that minor damage would be unlikely or perhaps confined to a very small fraction of structures and that major damage would be highly improbable
321 Threshold Cracking The US Bureau of Mines (Syskind Staggg Kopp and Dowding 1980) has defined threshold cracking limits for blasting-induced peak particle velocities (PPV) or peak ground velocities (PGV) to avoid cosmetic damage These threshold cracking limits as a function of the principal frequency are provided in Figure 3-1 The principal frequency is usually determined by zero-crossings of the waveform (controlled primarily by the response of the stratified earth) The limit is typically given as peak particle velocity or PPV which is often applied to building foundations and structures as well as ground near to but not adjacent to the structure For the purposes of this document PPV is assumed to be equivalent to PGV for all practical purposes unless otherwise stated The limit would apply to the ground surface in the absence of structures The PPV of the foundation structures should generally be less than the free surface PGV The limit of 19 mmsec (075 insec) between 4 and 16 Hz is for gypsum board walls while the limit of 125 mmsec (05 insec) between 28 and 10 Hz is for plaster walls Plaster walls are generally of older construction are unreinforced and thus crack more readily than modern gypsum board walls with taped joints The difference between threshold cracking criteria for gypsum board walls and plaster walls is small compared to the uncertainties inherent in the prediction of actual cosmetic cracking Interior surfaces trimmed with wood panels or un-finished interiors would withstand higher levels of vibration Tiled surfaces are generally backed by core board gypsum board or other substrate that resists cracking for which the limit shown for gypsum board may apply PGAs of 0025 g 005 g 01 g and 02 g are also plotted in Figure 3-1 Using a comparison of MMI with PGA adapted from Wald (1999) the Modified Mercalli Intensities (MMI) corresponding to these constant acceleration curves are indicated in Figure 3-1 The MMI scale describes qualitative effects of seismic ground motion and are compared with PGA and PGV in Table 3-2 Wald (1999) provides relationship between MMI as defined by Richter (1958) and PGA and PGV based on a regression analysis of horizontal ground motions for various seismic events in California Assigning a PGA or PGV to an MMI (or vice versa) is subject to considerable uncertainty The observations given in Table 3-2 were obtained from Richter
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-3
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
(1958) because Wald (1999) cited Richter in defining the MMI The observations assigned by the USGS to each MMI differ slightly from those defined by Richter (1958)
Table 3-2 Modified Mercalli Intensity and Peak Ground Acceleration (Wald 1999)
MMI Description PGA g
PGV-mmsec
Observations (Richter 1958)
III Weak 00017 to 0014
1 to 11 Felt indoors Hanging objects swing May not be recognized as an earthquake
IV Light 0014 to 0039
11 to 34 Hanging objects swing Vibration like passing of heavy trucks or sensation of a jolt like a heavy ball striking the walls Standing motor cars rock Windows dishes doors rattle Glasses clink Crockery clashes In the upper range of IV wooden walls and frame creak
V Moderate 0039 to 0092
34 to 81 Felt outdoors direction estimated Sleepers awakened Liquids disturbed some spilled Small unstable objects displaced or upset Doors swing close open Shutters pictures move Pendulum clocks stop start change rate
VI Strong 0092 to 018
81 to 160
Felt by all Many frightened and run outdoors Persons walk unsteadily Windows dishes glassware broken Knickknacks books etc off shelves Pictures off walls Furniture moved or overturned Weak plaster and masonry D cracked Small bells ring (church school) Trees bushes shaken
VII Very Strong 018-034
160 to 310
Difficult to stand Noticed by drivers of motor cars Hanging objects quiver Furniture broken Damage to masonry D including cracks Weak chimneys broken at roof line Fall of plaster loose bricks stones tiles cornices un-braced parapets and architectural ornaments Some cracks in masonry C Waves on ponds water turbid with mud Small slides and caving in along sand or gravel banks Large bells ring Concrete irrigation ditches damaged
VIII Destructive 034 to 065
310 to 600
Steering of motor cars affected Damage to masonry C partial collapse Some damage to masonry B none to masonry A Fall of stucco and some masonry walls Twisting fall of chimneys factory stacks monuments towers elevated tanks Frame houses moved on foundations if not bolted down loose panel walls thrown out Decayed piling broken off Branches broken from trees Changes in flow or temperature of springs and wells Cracks in wet ground and on steep slopes
Masonry A Good workmanship mortar and design reinforced especially laterally and bound together by using steel concrete etc designed to resist lateral forces
Masonry B Good workmanship and mortar reinforced but not designed to resist lateral forces Masonry C Ordinary workmanship and mortar no extreme weaknesses like failing to tie in at corners
but neither reinforced nor designed to resist horizontal forces Masonry D Weak materials such as adobe poor mortar low standards of workmanship weak
horizontally
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-4
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
The PGV limit shown for plaster-walled structures between 10 Hz and 40 Hz corresponds to a constant zero-to-peak (0-P) displacement limit of 02 mm (0008 in) This is a relatively trivial displacement that structures should be able to tolerate even though the associated peak ground acceleration at 40Hz is well above an MMI of VI This suggests that the MMI scale is poorly correlated with PGV at spectral peaks above 10 Hz The USBM vibration limits shown in Figure 3-1 indicate a decreasing PGV (or PPV) limit with decreasing frequency below 25 Hz This variation corresponds to a constant zero-to-peak (0-P) displacement curve of 08 mm (0032 in) At these low frequencies dynamic strains within buildings should be proportional to the ground acceleration rather than ground displacement The USBM criteria for threshold damage are widely used for construction vibration and blasting vibration monitoring but the constant displacement limit shown below 25 Hz is both puzzling and not well founded A review of USBM RI 8507 suggests that the constant displacement below 25Hz is not clearly supported by measurement data or correlation of any such data with building damage The USBM criterion curve is actually recommended as an ldquoAlternative Blasting Level Criteriardquo in Appendix B of RI 8507 with the statement that ldquoAn ultimate maximum displacement of 0030 inch (presumably zero-to-peak) is recommended which would only be of concern where very low frequencies are encounteredrdquo The report also reviews various literature concerning low frequency ground motion such as by Thoenen and Windes (1942) However Thoenen and Windes (1942) indicate that an acceleration limit of 01g is safe down to at least 2Hz Other references referred to in USBM 8507 are discussed with reference to ldquolow frequenciesrdquo that are not defined No examples of threshold damage are presented for PGVs of less than 125 mmsec (05 insec) at frequencies below 25Hz Thus applying the 08 mm (0032 in) 0-P criterion at frequencies below 25 may be unreasonable and if so would place severe and unnecessary restrictions on EGS-induced seismicity where such events would include low frequency ground motion Rather building damage criteria for ground motion of any kind at frequencies below roughly 25Hz should be based on experience with earthquake ground motions Accordingly a composite building damage criterion curve is suggested in Figure 3-2 to address the inconsistancy between threshold cracking limits and seismological experience The criterion is equivalent to the USBM RI 8507 criterion curve above 25 Hz Below 25 Hz the curve is drawn such that a constant acceleration of 002g with respect to frequency equates to the PGV criterion of 125mmsec (05 insec) at 25 Hz The criterion curve of 002 g shown below 25 Hz is comparable to an MMI of IV The PGV criterion of 125mmsec between 25 and 10 Hz also corresponds to an MMI of IV as indicated in Table 3-2 That is the suggested threshold cracking criterion of Figure 3-2 is consistent with an MMI IV The modified curve thus rationalizes the MMI scale with the USBM RI 8507 building threshold damage criteria with some degree of conservatism The minimum of 125 mmsec (05 insec) of the curve between 25 and 10 Hz corresponds to the typical range of resonance frequencies of wood-frame structures This curve is suggested as an appropriate PGV threshold cracking criterion for EGS-induced seismicity one which is based on experience with seismic ground motion as well as mining- and construction-generated ground motions and one which is generally considered conservative for a wide variety of wood-frame structures
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-5
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
The threshold damage criterion is given as a function of frequency for which an estimate of the spectral peak associated with the PGV is needed The determination of the spectral peak of the PGV is typically made by counting ldquozero-crossingsrdquo of the velocity motion This method is subject to some interpretation where the velocity waveforms contain substantial high frequency content but it is widely used in the blasting and construction industry More sophisticated techniques apply Fourier analysis to the transient velocity waveform to define the spectral peak The quantity plotted in Figure 3-2 against the criterion curve is the magnitude of the velocity waveform along the vertical axis and the spectral peak along the horizontal axis
Neglecting the maximum permissible PGV at 40Hz and higher frequencies (50mmsec) one may simply determine the vector-sum PGA PGV and zero-to-peak (0-P) ground displacement by differentiation and integration of the velocity waveforms If all three of these amplitudes exceed respectively 002g 125mmsec and 02mm 0-P (04 mm P-P) then the event would be in excess of the suggested threshold cracking criterion regardless of the spectrum If any one or more of these peak amplitudes did not exceed its respective threshold then the ground motion might be within the threshold cracking limit This would be a less-than-conservative test but would not require determination of a spectral peak by counting zero-crossings or Fourier analysis thus simplifying real-time data analysis and interpretation Additional investigation of this technique is needed High amplitude PGVrsquos at spectral peak frequencies in excess of 40Hz are likely to be rare However if this does occur then an additional criterion would be a maximum PGV of 50mmsec if the 0-P displacement is less than 02 mm respectively Adjustment of these acceleration velocity and displacement thresholds might be appropriate based on a review of seismic waveforms and local building types However distinction between building types (for example wood frame or masonry) is usually not made when applying criteria Figure 3-3 is an example output of an Instantel Minimate blast vibration monitor that illustrates the velocity waveform and PGVs plotted against the USBM criteria This chart is typical of the type of output that is used for monitoring blasting- and construction-related transients as well as continuous vibration The PGVs in three orthogonal axes are listed together with the vector sum The peak vector sum indicates the maximum PGV in any direction This type of display can be used for assessing EGS-induced seismicity though the modified criterion curve of Figure 3-2 is suggested here in lieu of the USBM RI 8507 criteria shown in Figure 3-1 and Figure 3-3
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-8
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
Figure 3-3 Example Event Report
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-9
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
322 Minor and Major Damage Dowding (1996) summarizes work by Edwards and Northwood (1960) and Northwood et al (1963) who characterize minor and major damage Minor damage would include superficial damage not causing weakening of the structure but would include broken windows loosened or fallen plaster and hairline cracks in masonry Minor damage would be associated with a moderate earthquake of MMI VI or higher
Major damage would include serious weakening of the structure This would be indicated by the presence of large cracks or shifting of the foundation or bearing walls or major settlement resulting in distortion or weakening of the superstructure Dowding (1985) indicates that threshold cracking occurred in older structures at about 76 mmsec (3 insec) minor damage at 114 mmsec (45 insec) and major damage at 203 mmsec (8 insec) The spectral frequencies associated with these damages were not identified From these examples a reasonable criterion for major damage would be 125 mmsec (5 insec) However damage at lower amplitudes of PGV may occur and would depend on the quality of construction age condition etc For example unreinforced masonry structures may be more prone to structural damage than modern reinforced masonry structures Construction vibration damage criteria for historical structures are generally lower or more restrictive than those of modern structures even though historical structures may easily withstand substantially greater motion than modern structures of the same type Minor and major damage to residential wood frame and masonry structures should be nil if EGS seismicity remains within threshold cracking criteria Hazard and risk assessment methods are described in Sections 5 and 6 respectively
33 DAMAGE CRITERIA FOR CIVIL STRUCTURES Civil structures include the following
Dams Bridges
Highways Railroads
Tunnels Power Plants
Pipe Lines Runways
Damage criteria for civil structures would depend on the nature of the structure Modern civil structures are by regulation designed to withstand substantial earthquake ground motions Ground motions induced by EGS activities are not expected to exceed those of natural origin in seismically active areas Hence damage due to EGS seismicity would not be expected to damage civil structures such as those listed above if they are designed to seismic codes for seismic areas The construction design drawings and specifications should be reviewed for seismic design criteria that may be applicable to EGS seismicity However seismic criteria may be defined in
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-10
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
terms of acceleration and are probably excessively conservative for frequencies above 10Hz (See the discussion above regarding Figure 3-2)
34 DAMAGE CRITERIA FOR BURIED STRUCTURES The estimate of probable damage to buried structures is based on the strain induced by the passing seismic shear wave and the strength of the material forming the structure The strains due to passing shear waves in buried structures can conservatively be assumed to be the same as those of the surrounding soil Buried structures are not subject to resonance amplification in the same manner as a building due to the loading of the soil and damping related to re-radiation of waves into the soil by the structure Thus buried structures should withstand much higher ground motion amplitudes than those that would damage surface structures Dowding (1996) discusses vibration damage to buried structures in some detail The probability of damage should be based on expected maximum ground strains and the flexibility of the buried structures which may require finite-element analysis In any case EGS seismicity that would not cause cosmetic damage to surface structures would very likely not damage underground structures
341 Wells Dowding (1996) describes results obtained from a USBM study concerning water wells The study indicated no loss of well capacity with PGVs produced by blasting as high as 84 mmsec (33 insec) and no loss of water level with PGVs as high as 141 mmsec (55 insec) This does not stop well owners from claiming that construction-related vibration damages their wells Thus inspection of deep water wells prior to project implementation should be conducted to assess well condition prior to EGS stimulation This pertains to ground motions dewatering or changes to aquifers are another matter to be considered by others
342 Pipelines Failure of gas transmission lines due to weld failures and other defects are of concern with respect to pipeline operations Relatively large tensile hoop stresses in the pipe wall due to high pressure gas would be superposed with strains induced by passing ground motion waves Old pipelines especially those manufactured with welded seams have some history of rupturing under excessive pressure However a properly maintained and designed pipeline should offer substantial margin of safety against normal soil movement over time with resulting strains in the soil that may exceed those associated with passing low amplitude seismic waves from induced seismicity
Assuming a shear-wave velocity in soil of 200 msec and PGV of perhaps 025 msec (10 insec) the peak strain in the soil due to the passing wave would be on the order of 025200 = 000125 giving a stress in the pipeline wall of 260 MPa (37500 psi) comparable with the yield strength of mild steel Designing an EGS project to limit PGVs to threshold damage criteria on the order of 50 mmsec (2 insec) would give a peak stress in the steel of 22 MPa (7500 psi) well within the yield strength of mild steel Dynamic stresses in the pipe wall should be less due to the higher modulus of the steel relative to that of the soil though a complete analysis would include the stresses due to pressurization
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-11
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
Dowding (1996) describes pipe wall strain measurements conducted during blasting at short range PGVs on the order of 114 msec (45 insec) produced strains in the pipe wall on the order of 500E-6 giving a pipe wall stress on the order of 100 MPa (15000 psi) Scaling down to PGVs on the order of 5 insec would imply a pipe wall stress of 12 MPa (1700 psi) a relatively small amount Again the seismically induced stresses must be combined with operating pipeline wall stresses due to pressure
As with any civil structure pipelines would be expected to be constructed to meet large ground motion seismic criteria Pipeline plan and profile drawings operating pressures and fluid types should be reviewed and discussed with the pipeline operator Gas transmission lines in poor condition should be identified and considered carefully Inspection of any nearby gas transmission line may be considered prior to EGS startup
343 Basement Walls Basement walls are usually constructed of either concrete block or reinforced concrete Dowding (1996) indicates that the former exhibited cracking of mortar joints at 75 mmsec (3 insec) Reinforced concrete walls cracked when the PPV exceeded 250 mmsec (10 insec) though in this case the failure was at the juncture of two walls
Again EGS projects designed to limit PPV or PGV to threshold cracking criteria should cause no cracking of basement walls The existing conditions of basement walls and structures should be documented with pre-construction surveys prior to EGS stimulation
344 Tunnels Dowding and Rozen (1978) summarize damages to tunnel structures of various types caused by earthquakes The summary considers 71 tunnel structures and 13 different earthquakes with Richter magnitudes ML 58 to 83 and with focal depths ranging from 13 to 40 km The review included four types of tunnels (a) unlined rock tunnels (b) temporary steel liners with wood blocking (c) final concrete lining and (d) final masonry lining The conclusions are
(1) Tunnels are less prone to seismic damage than surface structures for a given surface ground motion
(2) No damage to tunnels of any type occurred for estimated ground surface PGVs of 02 msec (8 insec) and PGAs of 019 g
(3) In cases where shaking was identified as causing tunnel damage the tunnels were in ground or rock of poor condition
(4) Total collapse of a tunnel was found only in cases of an intersecting fault and (5) Tunnels are much safer than surface structures for the same intensity of shaking
However the estimated ground motions are for the ground surface and lower amplitudes of ground motion likely occurred at tunnel depth Some amplification of tunnel stresses might occur for seismic wavelengths comparable with the tunnel diameter Tunnels in soil with liquefaction potential or tunnel portals near landslide-prone areas or tunnels intersected by faults or poor soil or rock conditions are at greater risk than tunnels in competent rock or tunnels with concrete liners and grouted soil Tunnels within an EGS seismic zone should be identified and reviewed with the responsible agencies to determine damage potential A survey of any such tunnels
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-12
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
should be conducted as part of the EGS impact assessment Tunnels may include (but not be limited to) railroad highway mining or water transport tunnels Tunnels should be inspected prior to EGS activities to identify pre-existing defects cracks seepage etc
35 LANDSLIDE AND ROCKSLIDE Landslides and rockslides caused by ground motion are difficult to predict though they have been documented in the case of large earthquakes Landslides may involve very slow movement of soil over time or may be abrupt as with an avalanche Rock slides may involve an avalanche of rock or the occasional motion of rocks or boulders that after a period of time result in the accumulation of rock mounts and slopes
Loose rock such as talus slopes may be viewed as colluvium deposited at its angle of repose Ground motions associated with blasting are usually too small to cause landslides of colluvium However the potential for rockslide in response to ground motion exists This is of particular interest to highway construction engineers for blasting at the base of talus slopes Landslide triggering associated with strong-motion seismic events of the order of M 6 or higher is discussed by Wieczorek (Transportation Research Board 1996) Evidently landslide triggering by smaller events is relatively rare Historical seismicity should define an acceptable limit for PGVs associated with EGS
36 HUMAN RESPONSE Human response to ground vibration includes perceptible vibration and low frequency ground-borne noise one or both of which are common with rail transportation construction and mining operations Some of the substantial literature that exists for human response to floor vibration and ground-borne noise caused by these sources is applicable to transient induced seismicity specifically that regarding mining and construction activities Evidently both ground motion and ground-borne noise from EGS activity near Basel Switzerland has caused human annoyance and the literature regarding this should be consulted Criteria for assessing the significance of vibration and ground-borne noise are discussed below
361 Third Octave Filters Third octave filters are commonly used for assessing human response to both noise and vibration (Third octave filters are also used for describing the vibration tolerance of sensitive instrumentation as discussed below) A third octave filter is a unity-gain filter with a bandwidth of approximately 23 of its nominal center frequency The third octave filter response is ldquomaximally flatrdquo with typically a 6-pole filter roll-characteristic of 36dB per octave outside of the filter pass-band Third octave filters are normally provided with high quality commercial sound level meters or vibration analyzers and can be used in a practical manner for monitoring of ground motions The responses of third octave filters are specified in ANSI Standard S111-2004 (R2009) The response time of a third octave filter increases with its order and is inversely proportional to its bandwidth That is the response time of 6th order filter is longer than the response time of a 3rd order filter Older analog third octave filters were usually 3rd order and referred to as Class III filters in the ANSI standards Modern digital sound and vibration meters almost universally provide 6th order filters The response time is important for short-period transient events such as
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-13
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
those produced by induced seismicity A third octave filter with center frequency of 4 Hz will have a filter bandwidth of slightly less than 1-Hz with a corresponding response time of the order of one second Induced seismic events by EGS projects will likely have durations less than one second The averaging time used for measuring the root-mean-square vibration needs to be long enough to include the filter response time The vibration ldquodoserdquo analysis approach discussed below is intended to circumvent this issue
362 Vibration
Metrics ISO 2631-1 (1997) is a standard for assessing human response to acceleration for people standing sitting or lying Frequency weightings are specified for application to third octave vibration acceleration spectra extending from 05 to 80 Hz together with methods for combining the weighted acceleration in all six degrees of freedom Two procedures are recommended in ISO 2631-1 for assessing transient acceleration the running RMS evaluation method and the fourth-power dose method The running RMS method involves determining the RMS amplitude of the weighted acceleration continuously with an integration time of one second Exponential weighting with respect to time may be employed The maximum RMS amplitude occurring during a transient event is called the Maximum Transient Vibration Value (MTVV) The fourth-power vibration dose is defined as the fourth root of the integral with respect to time of the weighted acceleration amplitude raised to the fourth power This approach is intended to represent the peak value within a given time period
Siskind et al (1980) suggest using a second-power vibration velocity dose computed by integrating the square of the vibration velocity amplitude over the entire signature with respect to time As with the fourth power approach this method is also independent of the integration time The integration times used in the dose procedures must be short enough to avoid introduction of background vibration into the estimate In the absence of background vibration the result would be independent of the integration time provided that the integration time covers or spans the duration of the transient event The second-power dose approach may be used with virtually any good quality sound level meter or vibration analyzer and the results should be comparable with the ISO 2631 fourth-power dose Some sound level meters or vibration analyzers can measure the fourth-power dose
ISO 2631-2 (2003) recommends limits for human exposure to vibration in buildings using the measurement methods outlined in the ISO 2631-1 standard The standard recommends a single weighting network or filter to be applied to analog ground acceleration to obtain the weighted acceleration regardless of the axis of vibration The filter is a simple low-pass filter with corner frequency of 56 Hz giving a constant acceleration response below 56 Hz and a constant velocity response above 56 Hz Band limiting filters are also recommended with corner frequencies of 08Hz (high pass) and 100 Hz (low pass) to define the overall bandwidth The filter response is tabulated at third octave band center frequencies for application to third octave acceleration data The 08 Hz high pass and 100 Hz low pass filters are probably unnecessary as
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-14
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
the spectral peak of EGS seismic acceleration and velocity associated with induced seismicity by EGS projects would likely be between 1 Hz and 100 Hz
ANSI S271-1983 (R2006) recommends third octave acceleration and velocity base-response curves for characterizing human response to vibration referring to ANSI S318-1979 The third octave acceleration and velocity base-response curves are plotted in Figure 3-4 and Figure 3-5 respectively The base-response curves are approximately twice the threshold of perception Base-response curves are provided for each axis and a composite curve is also recommended (ANSI S318-1979 is no longer in publication as of this writing supplanted by ANSI S272-1 which primarily follows ISO 2631-1) A simple (single-pole) low-pass filter response function is recommended in ANSI S271 for filtering analog acceleration data equivalent to the weighting function recommended in ISO 2631-2 (2003) but without band limiting filters at 08 and 100Hz The corresponding filter for analog velocity data would be a (single-pole) high-pass filter with corner frequency of 56Hz The ANSI S271 standard suggests that the root-mean-square (RMS) amplitude should be determined over the duration of the transient which for EGS seismicity would typically be of the order of a second or less
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-15
FREQUENCY - HZ 1 10 100
Z-AXIS ACCEL XY AXIS ACCEL COMBINED-AXIS ACCEL
1
10
100
1000 1
3 O
CTA
VE R
MS
AC
CEL
ERA
TIO
N
mmsec2
1010
100 g
10
1
01
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
Figure 3-4 Base Response Limits for Whole-Body Third-Octave Acceleration Exposure ndash Derived from ANSI S271
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-16
1 10 100
FREQUENCY - HZ
Z-AXIS VELOC XY-AXIS VELOCI COMBINED-AXIS VELOC
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
13
OCT
AVE
RM
S VE
LOCI
TY -
MM
SEC
1
01
Figure 3-5 Base Response Limits for Whole-Body Third-Octave Velocity Exposure ndash Derived from ANSI S271
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-17
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
Examples Figure 3-6 illustrates two example seismograms One is the un-weighted ground surface acceleration (measured in one particular axis) and the other is the weighted acceleration obtained by low-pass filtering the acceleration with a single-pole (6 dB attenuation per octave) filter with corner frequency of 56Hz as recommended in ANSI S271 The peak amplitude of the weighted acceleration signal is less than the PGA by only a modest amount as much of the spectrum of the acceleration signature is above the corner frequency of 56Hz A shorter period acceleration transient with higher frequency content would produce a significantly lower weighted acceleration waveform Third octave spectra of the un-weighted acceleration are plotted in Figure 3-7 The acceleration spectra are the peak the fourth-power dose the second power dose and the MTVV of the third octave band filtered signals The corresponding values for the overall (broadband un-weighted) PGA the overall fourth-power acceleration dose the overall second acceleration dose and the overall MTVV are plotted at the left hand side of Figure 3-7 The corresponding weighted peak acceleration the weighted fourth-power acceleration dose the weighted second-power dose and the weighted MTVV are plotted at the right-hand side
The fourth-power and the second-power dose curves are almost indistinguishable from one another suggesting that either the second-power acceleration dose approach or the fourth-power dose may be used for characterizing this particular transient ground motion The peak values of the overall and weighted acceleration are roughly about 50 to 100 higher than either of the dose magnitudes The MTVV (the maximum root-mean-square amplitude determined over any one-second time period) is generally significantly less than the dose magnitudes This makes the dose approach most attractive for event characterization relative to human response However the dose units include the square root of or fourth root of time and thus differ from the MTVV units which is a root-mean-square acceleration The third octave analyses indicate that the acceleration dose is between 64 and 128 times the ANSI S271 base response curve and thus highly perceptible to humans The peak third octave acceleration is plotted for illustration but should not necessarily be used for comparison with the ANSI S271 base response curve as these specifically apply to RMS third octave acceleration or dose Even so the peak values are not much greater than the dose values
The spectrum of this particular seismogram is such that its peak occurs at the transition frequency between constant acceleration and constant velocity regions of the ANSI curves As a result employing only the acceleration or velocity for assessing human annoyance potential is not entirely adequate However filtering the acceleration signal with a 56-Hz low pass filter as recommended in ANSI S271 and ISO 2631-2 provides a single number of weighted acceleration for assessing human annoyance potential The weighted accelerations are plotted at the right hand side of Figure 3-7
Measurement Location The ISO 2631-2 and ANSI S271 standards recommend measuring vibration acceleration (or velocity) in the buildings in which people would be located This may be impractical for EGS monitoring activity and would be difficult from a prediction point of view because building
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-18
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
response may vary considerably from one to the next The most practical approach for both prediction and monitoring would be to use the ground surface acceleration
Sidewalks and asphalt surfaces are ideal measurement surfaces for monitoring EGS vibration as the sidewalk has a large bearing surface relative to its mass assuming intimate contact between sidewalk and soil Transducers buried in pits at a depth of at most 1 m provide excellent permanent monitoring points However the back-fill of the pit must be of the same density as the surrounding soil That is the transducers should not be encased in concrete blocks that are in turn buried in the soil as the massive concrete block and soil will act as a spring-mass isolation system with a damped resonance of the order of perhaps 10 to 30Hz This may be acceptable for strong-motion seismicity with spectral peak at 3Hz but could be problematic for high spectral peak events From a practical point of view the building interior floor vibration acceleration or velocity will be roughly one to two times the exterior ground surface velocity or acceleration This comparison may be the result of measuring too closely to the foundation of the building as the ground surface response is reduced by the presence of the building foundation Considerable uncertainty exists in characterizing building response to vibration and considering the large number of building types and people that may be present near an EGS project the better approach would be to estimate a reasonable amplification factor that is representative of the buildings in the area In the absence of more information one may simply take the ground surface incident acceleration as a first estimate especially for transient motions with spectral peaks at frequencies below the fundamental floor resonance frequencies of structures These fundamental frequencies are usually of the order of 12Hz or higher for residential wood frame structures The incident ground surface acceleration or velocity can be multiplied by a factor of two if an additional safety factor is desired
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-19
006
-006
-004
-002
0
002
004
AC
CEL
ERA
TIO
N -
G
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
10 11 12 13 14 15
TIME - SEC
ACCELERATION
WEIGHTED ACCELERATION
Figure 3-6 Example Ground Acceleration
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-20
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
Recommended Practice for Assessing Human Response to EGS Vibration The ISO 2631-1 ANSI S271 and ANSI S271 standards provide excellent guidelines for assessing building interior floor vibration Of the various methods the recommended approach is to employ a second-power acceleration dose method with a good quality precision integrating sound level meter or vibration meter or the fourth-power dose method as recommended by ISO 2631-1 As shown above the second-power dose method gives results that are very similar to the fourth-power acceleration dose method for transient events of the order of one second or less In the event that a transient duration extends several seconds both the second-power and fourth-power dose methods will reflect the effect of increasing transient duration ANSI S271 Acceleration
Examples of limits for third octave acceleration dose are listed in Table 3-3 in terms of multiples of the composite base response curve given in ANSI S271 The base response curve corresponds to third octave acceleration and velocity limits of 000036 g and 100 micronsec (01 mmsec) for frequencies below and above 56 Hz respectively These limits would be applied to third octave vibration acceleration dose as described above The composite acceleration base response curve is illustrated in Figure 3-4 and the corresponding composite third octave velocity base response curve is illustrated in Figure 3-5 Third octave acceleration data are plotted against these criteria curves in Figure 3-7 The dose responses shown in Figure 3-7 fall between 32 and 64 times the base response curve The prototype limits are given as a function of recurrence interval Thus events that recur over time periods of less than 10 minutes during the night would be acceptable provided that their third octave acceleration dose was within the base response curve Events recurring over a time period of less than one hour but not less than 10 minutes during the night would be acceptable if their acceleration doses were within twice the base response curve These limits would be multiplied by a factor of two for daytime periods The daytime limits are extended in multiples of two for larger time periods However the ability to control or predict the time of day during which an induced seismic event occurs is severely limited Therefore the night time limits should probably be applied as a conservative measure A maximum limit of 64 times the base the response curve is suggested as this would correspond to an RMS magnitude of 0023 g with a PGA of perhaps 005 g (MMI V) and would exceed the threshold cracking criterion
The limits listed in Table 3-3 may require adjustment based on hazard assessment accuracy practicality receiver type land use etc A similar table may be developed for hospitals nursing homes schools and other land uses where vibration may interfere with activity Also higher limits might be considered during EGS stimulation over a short period of time with more restrictive post-stimulation limits for production over much longer time periods though such an approach must be vetted with stakeholders Weighted Acceleration Dose Limits
The single number weighted acceleration approach is recommended to reduce the complexity of assessing human response to ground motion As indicated above this involves filtering the acceleration signal with a low pass single-pole filter with roll-off frequency of 56Hz as recommended in ANSI S271 The weighted acceleration should then be squared and integrated with respect to time over the transient duration The results should be summed over each axis and the square root of the sum should be taken to obtain the composite vector-sum dose This
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-22
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
process will generally yield a higher value that would be obtained by comparison of third octave spectra with the response curves
Prototype limits for weighted composite acceleration dose are listed in Table 3-4 The prototype acceleration limits are derived by taking the multiple of the base response curve acceleration limit at the low frequency limit (below 56Hz) and multiplying by the square root of two (+3dB) Thus the low frequency acceleration limit for the ANSI S271 acceleration base response curve at 2Hz is 000036 g and multiplying by 14 gives a weighted acceleration limit of 00005 g The factor of root two is intended to accommodate the difference between the weighted acceleration and the maximum value obtained in any third octave band which is necessarily less than the weighted acceleration (A more conservative and acceptable approach would be to not employ the factor of 14) An event with maximum weighted acceleration dose of 00005 g would be largely unnoticed Events of this nature would correspond to a weighted velocity of about 100 micronsec typically considered as a threshold impact on human occupancy though the threshold of human perception is actually less than this by perhaps a factor of two (ANSI Standard S271) Events of this type could occur repeatedly throughout the night without generating significant annoyance A weighted acceleration dose of 0001g occurring repeatedly through the day time period would probably be acceptable for daytime residential occupancy However above these dose amplitudes human annoyance may rise rapidly Repeated exposure to perceptible vibration with high occurrence rate (short recurrence period) would likely generate significant reaction A maximum dose of 0032 g-sec12 or 0032 g-sec14 is suggested as the PGA associated with such an even would be 005 g or 006 g corresponding to an MMI V and could be above the threshold cracking criterion of 002g Weighted Velocity Dose Limits
Table 3-5 contains prototype vibration dose limits that correspond to the prototype limits given in Table 3-4 The weighted vibration velocity would be obtained by applying a high-pass single-pole filter with corner frequency of 56 Hz to the velocity waveform This may be most appropriate for velocity data obtained with a 1-Hz or 2-Hz seismometer or geophone Typical EGS vibration is expected to have most of its energy at frequencies below 10 Hz Thus either the weighted velocity or the weighted acceleration are probably of equal merit The choice may depend more on transducer selection and instrumentation simplicity PGA and PGV Limits
Detailed prediction of EGS ground acceleration or velocity signatures with spectral content is perhaps impracticable whereas prediction of the PGA or PGV may be straight-forward given appropriate EGS seismic models and statistics Thus human annoyance may have to be based on PGA and PGV rather than weighted RMS or dose acceleration In this case the PGA and PGV would be about 50 to 100 higher than the un-weighted acceleration or velocity dose judging from the results given in Figure 3-7 If spectral characteristics can be predicted the weighted peak acceleration can be estimated in which case the prototype limits would be roughly 50 to 100 higher than the prototype limits shown for the weighted acceleration dose in Table 3-4 or the weighted velocity dose limits given in Table 3-5 If the joint probability of recurrence of an event with given un-weighted PGA and PGV can be predicted then the PGA and PGV may be compared directly with the limits given in Table 3-4
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-23
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
and Table 3-5 respectively perhaps with a multiplier of two to account for peak versus RMS magnitudes to determine an acceptable recurrence period As an example if events with predicted PGAs and PGVs in excess of 0001 g and 0280 mmsec respectively are predicted to recur within ten minutes then the suggested night time criterion would be exceeded On the other hand if either the un-weighted PGA or the PGV or both are less than 0001 g and 028 mmsec then the event would be within the suggested criterion for a 10-minute recurrence interval The un-weighted PGA and PGV limits can be taken as twice the acceleration and velocity dose limits given in Table 3-4 and Table 3-5
Table 3-3 Suggested Criteria for Third Octave Ground Surface Acceleration Dose versus Recurrence Period
Time of Day
Multiple of Third Octave Composite Base Response Curve (Figure 3-4) for Residential Occupancy
ANSI S271 lt 10 Min lt1 Hr lt 8 Hr lt 24-Hr lt1 Week Maximum
Day 2 4 8 16 32 64 Night 1 2 4
Table 3-4 Suggested Weighted Acceleration Dose Limits versus Recurrence Period
Time of Day
Weighted Acceleration Dose Limits for Residential Occupancy g-sec12 or g-sec14
ANSI S271 Weighting lt 10 Min lt1 Hr lt 8 Hr lt 24-Hr lt1 Week Maximum
Day 0001 0002 0004 0008 0016 0032 Night 00005 0001 0002
Table 3-5 Suggested Weighted Velocity Dose Limits versus Recurrence Period
Time of Day
Weighted Velocity Dose Limits for Residential Occupancy (mmsec)-sec12 or (mmsec)-sec14
ANSI S271 Weighting lt 10 Min lt1 Hr lt 8 Hr lt 24-Hr lt1 Week Maximum
Day 028 056 112 224 448 896 Night 014 028 056
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-24
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
363 Ground-Borne Noise Ground-borne noise is radiated into rooms by vibrating walls and floors The interior noise is computed by estimating the input sound power resulting from vibrating surfaces accounting for radiation efficiency of various modes of wall vibration and accounting for the acoustical absorption present in the room As a practical matter the average absorption coefficient can be assumed to be 05 and the radiation efficiency of the room may be assumed to be 50 Thus without going into the details the interior third-octave band sound pressure in decibels relative to 20 micro-Pascal can be estimated by adding 32dB to the room surface third-octave band vibration velocity level in dB re one micronsec energy-averaged over the room surfaces That is for each third octave band
SPL (dB re 20 x 10-6 Pa) = VEL (dB re 10-6 msec) + 32dB Here SPL is the sound pressure level and VEL is the velocity level both in decibels This approach is employed for the prediction of ground-borne noise produced by rail transit systems (Federal Transit Administration 2006) The uncertainty in this conversion is roughly five decibels (Often the decibel is abbreviated as VdB in the US for example VdB relative to 1 micro-insec) (The ISO standard reference level for vibration velocity is 10-8 msec This may be preferable to using 10-6 msec as a reference level to maintain uniformity between international standards)
The room surface vibration velocity level is difficult to predict as it depends on foundation response to incident ground vibration and structure design (See above discussion regarding interior versus exterior vibration) The A-Weighted sound level is perhaps the most universal metric for assessing the noise environment of human beings as it has been employed throughout the world for well over 50 years The A-Weighted sound level is obtained by filtering the analog sound pressure with an A-Weighting network and analyzing the resulting signal with an RMS detector The A-Weighting network is universally provided with sound level meters so that monitoring EGS-induced ground-borne noise is entirely practicable However a precision sound level meter with low input noise and accurate response down to 10 Hz is needed for accurate assessment Other weighting networks are also provided such as the C-Weighting network that has been proposed by some for assessing low-frequency noise The C-weighting is essentially flat between 315 Hz and 8 KHz The response of the A-Weighting network is plotted in Figure 3-8
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-25
A-Weighting 35929 PM 7222011
16 316 63 125 250 500 1K 2K 4K 8K 16K
FREQUENCY - HZ
A-WEIGHTING
-70
-60
-50
-40
-30
-20
-10
0
10
RES
PON
SE -
DEC
IBEL
S
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
Figure 3-8 A-Weighting Network Filter Response
The A-Weighted sound level can be obtained by applying the A-Weighting response curve to the estimated third-octave band sound pressure spectrum and summing the third-octave band sound energies To do this one must estimate the spectrum of sound pressure Where no estimate is available a peak frequency of 31 Hz is perhaps adequate for small magnitude events recognizing that the peak could be at sub-audible frequencies The A-weighting response in decibels can also be added to narrow band spectra or Fourier power spectra given in decibels The adjusted spectral levels can then be energy-summed to obtain the A-weighed sound (Energy-summing is also known as ldquodecibel additionrdquo The energy in each band is 10(01L) These energies are summed over all bands The resulting sound level is then 10Log10 [sum of band energies])
Audible ground-borne noise due to EGS activities would be unlikely unless the loss factor of the surficial soil is low For example rock or very stiff glacial tills support efficient transmission of ground-borne noise from rail transit subway systems in Toronto The quality factor of these soils Q is of the order of 40 corresponding to a loss factor of Q-1 of 0025 Audible ground-borne noise would typically involve frequencies above 20 Hz below which frequency a personrsquos aural response is very low and decreases rapidly with decreasing frequency as illustrated by the A-weighted response curve given in Figure 3-8 Perceptible ground vibration with spectral peaks at 31 Hz and above may be particular audible Short-period low-magnitude seismic events can be
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-26
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
audible As a practical matter extending the measurement range down to include the 125 Hz third octave band is desirable to cover the sub-audible range Precision sound levels meters with high quality condenser microphones can extend the range down to about 4 Hz or even lower with special microphones
A limit of 35dBA averaged over the duration of the transient event is reasonable for residential occupancy where sleeping is a normal activity Lower limits of 25dBA would apply to concert halls or structures where low background noise is a basis for use However audible EGS-induced ground-borne noise may be infrequent in which case higher limits would likely be appropriate for these specialized public spaces especially in view of typical background noise due to HVAC systems door closings automobile and truck traffic and aircraft The limit might also be relaxed for residential structures located near highways with heavy truck traffic at night or near airports Seismic vibration events that are not perceptible may yet produce audible noise if the spectral peak frequency is high enough Conversely seismic events that are above the threshold of tactile perception may go un-noticed if the noise produced by such events is not audible above the background Audibility may be greater at night when background noise levels are least in which case greater awareness of ground vibration may exist
37 LABORATORY AND MANUFACTURING FACILITIES Ground vibration may impact sensitive laboratory and manufacturing equipment such as scanning electron micro-scopes (SEM) scanning transmission electron micro-scopes (STEM) photolithography machines electron deposition machines laser interferometers laser metrology systems machining equipment and the like The nature of such operations is such that manufacturing productivity may be lessened or in some cases prevented The impact would be increased cost of production due to higher product defect rates
371 Criteria Vibration criteria published by the Institute of Environmental Sciences are plotted in Figure 3-9 and listed in Table 3-6 for sensitive equipment Also plotted for comparison are vibration limits for typical spaces used for human activity The limits given in Figure 3-9 and Table 3-6 apply to third-octave band RMS velocities measured over the duration of the vibration event The time duration of transient vibration from EGS activities would be one second or less The typical practice for such transients is to analyze the transient waveforms continuously with an integration time of one second and choose the maximum value obtained for each third-octave band which is the MTVV discussed in the ISO 2631 standard This approach may be unnecessarily severe but is nevertheless practicable for transient analysis and is commonly employed In any case measurement procedures given in manufacturerrsquos specifications for sensitive equipment should be used if available
Custom Laboratory Apparatus Custom-designed laboratory experimental apparatuses common in university research laboratories are not necessarily designed to control floor vibration As a result custom laboratory equipment may be particularly sensitive to vibration for which no published criteria are available The limits given in Table 3-6 can be applied based on the descriptions of equipment and line-widths involved The limits relevant to sensitive equipment are labeled as
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-27
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
VC-A through VC-G and are recommended by the IES as floor vibration criteria for sensitive laboratory equipment
Figure 3-9 IES Vibration Criteria for Sensitive Equipment (IES-RP-CC012) (See Table 3-6)
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-28
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
Table 3-6 IES Vibration Criteria for Sensitive Equipment (IES-RP-CC012)
Equipment Category
Description Detail Size ndash
microns
10-6msec rms
Workshop (ISO)
Distinctly perceptible vibration NA 800
Office (ISO) Perceptible Vibration NA 400 Residential Day (ISO)
Barely perceptible Adequate for computer equipment probe test equipment and low power micro-scopes
75 200
Operating Theater (ISO)
Suitable for hospital operating theaters without OR Scopes optical microscopes up to 100X mechanical balances
25 100
VC-A Adequate for most optical microscopes up to 400X micro-balances optical balances proximity and projection aligners
8 50
VC-B Optical microscopes to 1000X inspection and lithography equipment to 3micron line widths
3 25
VC-C Photo-lithography and inspection equipment to 1micron line width scanning electron micro-scopes optical tables
1 125
VC-D Photo-lithography and inspection equipment to 300 nano-meter line width scanning electron micro-scopes at 100000X laser interferometers
03 63
VC-E Photo-lithography and inspection equipment to 100 nano-meter line width scanning electron micro-scopes at 100000X long-path laser interferometers1 scanning tunneling electron micro-scopes1
01 32
VC-F Scanning Transmission electron microscopes1 16
VC-G Scanning Transmission Electron microscopes at highest resolution atomic force micro-scopes atomic tweezers1
08
NOTE 1 These equipment are inferred by the writer
Medical Every major medical center today has one or more magnetic resonance imaging systems (MRI) that typically have low tolerance to ground motion Site specifications for vibration environments of MRIs are provided by manufacturers and should be reviewed to estimate the potential for vibration impact Each manufacturer has its own vibration tolerance specification and these vary from one model to the next Absent specific information the following limits on third-octave band vibration velocity measured in any 1-second interval (MTVV) represent reasonable criteria (based on the writerrsquos experience)
15 Tesla 125 micronsec (VC-C Table 3-6)
3 Tesla 63 micronsec (VC-D Table 3-6) The typical General Electric MRI (as of 2010) can withstand PGAs of up to 00005 g without requiring additional study PGAs due to EGS activities may exceed this criterion in which case
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-29
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
estimates of the spectral energy of the acceleration with a bin bandwidth of typically 0125Hz may be required for frequencies from 0 to 50 Hz the typical range of the GE specification These estimates would be compared with criterion curves specified by the manufacturer which criteria may be of the order of 100 micro-g at low frequencies
Other medical equipment that may be subject to vibration includes optical microscopes micro-balances operating room micro-scopes (OR Scopes) and other laboratory analysis equipment While these might be impacted by short transient ground vibration the nature of their use is such that observations might be repeated with little loss of efficiency A typical vibration velocity limit for such laboratory equipment would be an RMS velocity of 50 micronsec in any third-octave band between 5Hz and 100Hz measured over any one-second period (VC-A Table 3-6)
CT scanners and PET scanners while achieving high resolution do not appear to be particularly sensitive to vibration judging from an apparent lack of vibration tolerance specifications for these machines Even so frequent exposure of equipment to floor vibration in excess of 100 micronsec may interfere with operations A VC-A limit of 50 micronsec (RMS) may be appropriate Manufacturersrsquo specifications should be obtained for such equipment and carefully reviewed
The floor vibration criterion for operating theaters is indicated in Figure 3-9 to be 100 micronsec (4000 micro-insec) while the American National Standards Institute (ANSI-S271) recommends a limit to 70 micronsec (2800 micro-insec) Operating room microscopes due to their cantilevered supports must be supported or mounted at points where structural vibration is less than perhaps 125 micronsec (500 micro-insec) (VC-C) Modern OR scopes can be provided with gyroscopic stabilizers that increase their tolerance to vibration
Biological Research Many biological research institutions use medical mice and other animals for research purposes Of particular concern is maintenance of the environment of experimental and control mice to ensure that both experience the same environment Otherwise environmental differences may influence the outcome of an experiment This is a difficult area to assess though some progress has been made In any case vibration and ground-borne noise have become an issue for the assessment of transportation and construction vibration impacts on medical mice and other animals One may assume that laboratory researchers would be concerned over possible effects of EGS induced seismicity on medical mice
38 SUMMARY The assessment of seismic impact on human activity can be a daunting task and criteria for assessment should be simple and easily applied to ground motion and vibration estimates Fortunately ground-borne noise and vibration impact criteria are available from the transportation construction and mining industries that can be applied to seismic hazard estimates with little adjustment Doing so at an early stage in the EGS development process may facilitate acceptance and allow mitigation of adverse seismic impacts The preceding discussion summarizes the most widely used impact criteria and the EGS developer can draw upon the experiences gained in these other industries
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-30
SECTION THREE Step 3 Criteria for Damage Vibration and Noise
39 SUGGESTED READING Beranek L L (Editor) Noise and Vibration Control McGraw-Hill 650 p 1971 Barkan D D Dynamics of Bases and Foundations McGraw-Hill 434 p 1962
Dowding CH 1996 Construction vibrations Prentice Hall Richart F D Hall H R and Woods R D Vibrations of Soils and Foundations Prentice-
Hall 414p 1970 Siskind D E M S Stagg J W Kopp and C H Dowding 1980 Structure Response and
Damage Produced by Ground Vibration from Surface Mine Blasting US Bureau of Mines Report of Investigations RI 8507
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 3-31
4 Section 4 FOUR Step 4 Collection of Seismicity Data
SECTION FOUR Step 4 Collection of Seismicity Data
41 PURPOSE The purpose of this step is to gather the data on seismicity that will be needed to accomplish the objectives of the EGSGeothermal project Also included will be suggested goals for and means to process the data This section will deal primarily with seismic data It is obvious that to accurately estimate or forecast induced seismicity otherdata will aso be critical Examples will be stress data faults and lithology injection parametersetc Seismicity data will primarily be used for two related but different needs The first need is to address any issues related to the publicregulatory acceptance of any induced seismicity The second need is to aid in the design and successful operation of the EGS project In short the seismic data will be used not only to forecast induced seismic activity but also to understand induced seismicity for mitigation and reservoir-management purposes Not included in this step would be any collection or analysis of any active seismic data required to characterize the subsurface characteristics of the EGS system or surroundings (although the results of those efforts would be useful for processing the earthquake data)
42 GATHERING DATA TO ESTABLISH BACKGROUNDHISTORICAL SEISMICITY LEVELS REGIONAL
The first step in understanding the potential for induced seismicity as well as in providing data for the EGS design is to identify past and present natural seismicity These data will be needed for the induced seismicity hazard and risk analysis (Sections 5 and 6) as well as for understanding current stressfaultsfracture patterns For example Step 1 of the Protocol is to screen the potential EGS area for any obvious ldquoshowstoppersrdquo In areas of high naturalbackground seismicity it may be undesirable to consider developing an EGS project On the other hand if the EGS project is in a relatively unpopulated area the high levels of seismicity may indicate a high potential for EGS project success (zones of high fracture heat etc) Also the tolerance for seismicity in active seismic areas may be higher than in areas where the public has not experienced any significant levels of seismicity
This does not imply however that if the anticipated induced seismicity is not over background seismicity levels (in maximum size only) there will not be a public acceptance issue For example there may have been historical seismicity above magnitude 4 and even if the anticipated induced seismicity maximum seismicity is all below a 30 the number of events below 30 may cause public concern That is it is important to determine public acceptance levels of any induced seismicity
On the positive side if the potential EGS site is in an earthquake-prone area structures may have been built to more stringent codes than in areas of low seismic activity In any case the use and need for gathering historicalbackground seismicity will be specific to each area Background seismicity data will be needed at both the regional level and local level (scale of EGS project) Today almost all parts of the US are monitored with seismographic networks that are capable of detecting and locating seismicity at M 20 and above and in many areas at M 15 and above This is adequate for any background regional seismic studies but may not be adequate for local seismic studies at the individual EGS scale
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-1
SECTION FOUR Step 4 Collection of Seismicity Data
421 Possible Sources of Background Data In the US there have been a number of ongoing seismic monitoring programs run by the USGS as part of their National Earthquake Hazard Reduction Program (NEHRP) Access to the data is supplied through the USGS website httpearthquakeusgsgov A variety of other information is also available at this site such as Shake Maps risk estimates and other useful information that will be needed to assess hazard and risks of the seismicity In addition the USGS can provide links to other data sets that may be useful for understanding historicalbackground seismicity (httpearthquakeusgsgovother_eqsitesphp) By accessing these data sets the reader can specify the area and time period of interest While much of the data collected in the US is either sent to the USGS or to the data center operated by the Incorporated Research Institutes of Seismology (IRIS httpwwwiriseduhq) individual universities also operate their own seismographic networks such as CaltechUniversity of Southern California (Southern California Earthquake Center (SCEC) httpwwwdatascecorg UC Berkeley Seismographic Stations (httpwwwncedcorg) University of Nevada Reno (httpwwwseismounredu ) and the University of Washington (httpwwwesswashingtoneduSEISPNSN ) to name a few There also may be available data that was collected for ldquoprivaterdquo purposes These would include any seismic networks installed for locating or monitoring past or current geothermal resources or other natural resources State offices related to natural resources or oil and gas resources may also have records of such data Additionally the construction of critical structures such as large power plants dams or nuclear power plants may have required seismic studies These studies are often comprehensive and require detailed hazard assessments and thus could possibly provide the amount of information needed for EGS hazard assessments
If all else fails a background seismic study may be required specifically for the project This would require either installing a regional network or augmenting an existing network A large number of stations (more than five or six) would likely be unnecessary owing to the existing coverage of USGS and or other networks in the US
422 Data Requirements The time required for seismic monitoring (ie the amount of background data) and the magnitude range of the data will also depend on the area under study In general the developer would need enough data to perform a credible probabilistic seismic hazard analysis (PSHA) (Section 6) Accomplishing this would require sufficient data over a wide-enough magnitude range to derive the occurrence rate ie sufficient data to construct an accurate ldquob-valuerdquo from the data (Figure 4-1) This may require access to data that has been recorded over many years Correct calculation of the b-value is critical because it is related to the physical mechanisms of the earthquakes which is important to the hazard analysis (See httpadsabsharvardeduabs2006AGUFMS42C08F) A common mistake is to use a least-squares method for calculating the slope of the magnitude versus cumulative numbers of events plot rather than a maximum likelihood approach (Aki 1965) as well as not having a large-enough data set Note that there is no evidence for significant b value variation with location onoff of major faults in California (httppasadenawrusgsgovofficekfelzer AGU2006Talkpdf) Seismic data are also required to provide information on stress patterns that will affect the nature of any induced seismicity To provide useful data for both a PSHA and stress analysis a representative sampling of the earthquakes in the area of interest will be necessary A number often used is 2000 events for a
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-2
SECTION FOUR Step 4 Collection of Seismicity Data
credible b-value (httppasadenawrusgsgovofficekfelzerAGU2006Talkpdf ) In most cases it will be difficult to gather enough seismicity data to satisfy the 2000 event criteria ie if there have been no seismic networks in the area this will be difficult For example assuming a b-value of 10 and an occurrence rate of one M 20 per month it will be necessary to monitor down to M 00 for 20 months to gather enough data On the other hand if the b-value is 15 it will be necessary to monitor for several months In terms of enough data for stress analysis a few well-recorded tens of events (ie with enough azimuthal coverage to fill the focal sphere with good and well-defined first motions) would be necessary for calculating composite stress directions which would be useful for determining background stress levels in the area of interest
Figure 4-1 Earthquake Recurrence of The Geysers (b value = 125)
However recent studies have shown that if one has at least two orders of magnitude on a log-log plot then that may be sufficient to obtain a reliable b-value (Stump and Porter 2012) The area to cover will also depend on the specific site but the minimum should be (for the regional studies) an area that encompasses the maximum anticipated fault lengths that the EGS zone may be near For example if the EGS reservoir zone were ultimately anticipated to lie within a 5 km diameter circle it will be necessary to know what regional and local stresses are acting on this zone Within the Basin and Range Province we would want to know what the seismicity has been in a particular valley (for a horst and graben structure) and possibly in adjacent valleys In most regions of the US wider areas of seismicity are almost always available through the various
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-3
SECTION FOUR Step 4 Collection of Seismicity Data
data sources listed above In some instances adding a few stations to existing networks for 6 to 12 months may be necessary to ldquofill inrdquo data gaps
43 LOCAL SEISMIC MONITORING Once the EGS area has been narrowed down to potential well sites more detailed earthquake data will most likely be needed than are provided from the regional seismicity data Consequently local seismic monitoring should be undertaken at that time if it is not under way already Depending on what was performed as part of background monitoring this could be an expansion of an existing effort or a new effort The seismic monitoring will again be conducted for two main purposes for addressing public-regulatory concerns and for addressing optimal commercial development of the EGS resource Both require an understanding of earthquake mechanisms and causes The better that these can be understood the more confidence all stakeholders will have in ensuring that the EGS project is being operated in a safe fashion
431 Basic Requirements The basic information required will be
1 The location and time (x y z t) of the events
2 The magnitude of the events
3 Focal mechanisms of the events (not necessarily the full moment tensor see the discussion below on moment tensors)
4 Rate of seismicity (Gutenberg-Richter recurrence parameters)
5 Data provided in real time once the EGS project begins stimulation and production
It is best to strive for as much sensitivity and accuracy as is economically possible As in the case of background monitoring the regulatory needs will vary depending on the location of the project with respect to the location of any public or private ldquoassetsrdquo For example if the project is in a remote area that has a history of seismic inactivity (not a lack of monitoring however) the regulatory requirements may be minimal (see Step 3) However for operational needs it is advisable that detailed monitoring be carried out For both regulatory and operational needs the local seismic monitoring should be performed before during and after the injection activity to validate the engineering design of the injection in terms of fluid movement directions and to guide the operators with respect to optimal injection volumes and rates as well as any necessary mitigation actions Background and local monitoring will also separate any natural seismicity from induced seismicity providing protection to the operators against specious claims and ensuring that local vibration regulations are being followed It is also important to make the results of the local monitoring available to the public in as close to real time as possible especially during initial and ongoing injections that are designed to ldquocreate the reservoirrdquo The monitoring should be maintained at a comprehensive level throughout the life of the project and possibly longer If however the rate and level of seismicity decrease significantly during the project consideration can be given to discontinuing the monitoring soon after the project ends (after a few months)
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-4
SECTION FOUR Step 4 Collection of Seismicity Data
432 Instrumentation Needs and Data Coverage To meet the basic needs listed in (Section 431) the seismic array must be designed in light of the known background seismicity as well as the total extent and desired size of the EGS reservoir Other factors are of course the known stress fields fault locations depth of the EGS reservoir and seismic properties (attenuation and velocity of the formation) Although it was written in the early 1980s the book Principles and Applications of Microearthquake Networks by HK Lee and SW Stewart (1981) is an excellent reference In designing an array there will be tradeoffs among cost sensitivity and spatial coverage (ie boreholes may be necessary to derive the necessary sensitivity but may involve sacrificing spatial coverage) As new technology is developed (drilling and sensors) or as new processing methods are developed to ldquopull signal from noiserdquo such tradeoffs may become less of an issue In general an array of seismic sensors should have enough elements to have a location accuracy of 100 to 200 m in the horizontal dimensions and 500 m in depth Precision can be much better (few meters to a few 10rsquos of meters) using modern location schemes but uncertainty in earth models will determine accuracy Again this will depend on the size of the site and the nature of the recorded seismicity (rate magnitude ranges etc)
A typical EGS area with a 5 km diameter would preferably have at a minimum an 8-element array of seismic stations covering the 5 km area and a portion of the area outside of the target area especially if nearby faults and or public assets may be affected (Figure 4-2) Also it will probably be necessary to detect and reliably locate events down to M 00 or less Note that for regulatory purposes it may only be necessary to achieve the M 00 to 10 level but the lower the detection level the more ldquoheadroomrdquo there will be for mitigation control as well as more events for calculating occurrence rates (b values) which provide insight on failure mechanisms The goal is to have enough stations not only to locate the events to the desired threshold but to calculate focal mechanisms and (if necessary) moment tensors Seismologists use information from seismograms to calculate the focal mechanism and typically display it on maps as a beach ball symbol This symbol is the projection on a horizontal plane of the lower half of an imaginary spherical shell (focal sphere) surrounding the earthquake source (A) A line is scribed where the fault plane intersects the shell Because the stress-field orientation at the time of rupture governs the direction of slip on the fault plane the beach ball also depicts this stress orientation In this way it is possible to define the tension axis (T) which reflects the minimum compressive stress direction and pressure axis (P) which reflects the maximum compressive stress direction (httpearthquakeusgsgovlearntopicsbeachballphp) These studies may have been done to select the target EGS area but if not these data will be required to perform that particular analysis for estimating the nature and potential of any induced seismicity
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-5
SECTION FOUR Step 4 Collection of Seismicity Data
Figure 4-2 Example Local Seismic Array Moment tensor calculations (httponlinelibrarywileycomdoi101111j1365-246X1976tb04162xabstract) are useful for deriving the characteristic earthquake process which may be useful in determining how the fracture creationslip is occurring during the stimulation activities which in turn may be useful in guiding injection activities However reliable moment tensor calculations require a denser coverage of stations than the location and focal mechanism solutions used in ldquomonitoringrdquo arrays (which would only provide the basic requirementsmdashhttpwwwduracukgrfoulgerOffprintsRossGRL1996pdf) This is because the reliability and accuracy of the moment tensor solutions are a function of how comprehensive the radiation pattern has been captured Up to two times the number of stations may be required to gain enough data for reliable moment-tensor calculations This may be achieved by installing temporary ldquoin-fillrdquo stations deployed during main injections or when there is a change in injection patterns Obtaining reliable moment tensor solutions with small microearthquake networks is not straight forward with high frequency data such solutions require detailed (100 to 200 m resolution) velocity and attenuation models (Greenrsquos functions) Ideally data would be gathered from 10 Hz up to the maximum content of the small events (which could be as high as 100 Hz or more especially if borehole deployments are used)
433 Instrumentation and Deployment Collecting and analyzing the necessary data requires the proper sensors electronics and computational capability Again there are two broad reasons for collecting the data for (1) regulatory and (2) operational needs Except for strong motion data the requirements will be the same at the regional and local scales For regulatory needs local monitoring should also include
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-6
SECTION FOUR Step 4 Collection of Seismicity Data
less sensitive recorders mainly for recording ground shaking that can approach or surpass the threshold of human perception Typically this is achieved by installing a few strong-motion recorders near any sensitive structureslocal public assets to record vibrations that may be problematic and to monitor ground motion as a function of event magnitudes geologic structure and proximity of the events to items identified by the regulatory agencies Ideally a weak-motion array (instruments more sensitive than the strong motion recorders) would record data with a broad bandwidth (ldquoflatrdquo in the range of 1 Hz to several hundred Hz) with low noise (equivalent to 100 nano grsquos per root hertz) on three-component sensors (X Y Z) with at least 24-bit dynamic range and installed in boreholes that allows 60 dB reduction in surface noise However to do so would require multiple types of sensors in the borehole If the borehole were in a hot zone (greater than 100degC) the technology may not be available However sensors based on advanced technology (fiber optic) may soon be available (in 2013) at a reasonable cost In terms of current technology the standard technology of using geophones with modern digitizers is currently the best choice in the few Hz to a few hundred Hz range Accelerometers are also available (piezoelectric or force balance based) but more costly than and not as robust as geophones but do provide a good flat frequency response over a broad frequency range If boreholes are not available modern three-component 2 Hz phones are the best choice For higher frequency data exclusively the standard three-component 45 Hz phones are also acceptable If boreholes are available (100 m to 150 m depth or deeper) it is best to use ldquoomnidirectionalrdquo geophones which are capable of recording higher frequency data Because most boreholes are not exactly vertical (ie they deviate) the higher frequency geophones are smaller and thus will fit into slimmer boreholes and can tolerate more tilt (15deg or more) However most borehole phones have a 8 Hz corner frequency response (3 dB point) thus sacrificing low frequency data Lower frequency sensors are available using gimbaled geophones or accelerometers but they are more expensive (a few thousand to ten thousand dollars) but the expense may be worthwhile to collect the necessary data
The exact instrumentation will again depend upon the expected seismicity levels Experience to date indicates the need for reliably detecting seismicity from M -10 up to M 40+ range If the instrumentation can detect and locate M -10 events it is obvious that it can also detect and locate the larger events but ldquoclipped datardquo in the upper magnitude ranges must be avoided Thus attention must be paid to the dynamic ranges of the sensors as well as to the digitizing and recording electronics Also attention must be paid to the digitization rates of the data ie for small arrays timing to the millisecond may be necessary to accurately locate the events as well as to prevent aliasing the data Therefore the electronics should digitize at a rate of at least 500 samplessec obtaining 24-bit resolution from sensors with 120 dB of dynamic range In addition the data must be time stamped with a common time base as it is collected
Most seismic arrays are set up such that solar-powered electronics are deployed at each sensor site (be it a surface sensor or a borehole sensor) (Figure 4-3) The practice now is that the data from each site are digitized time stamped and sent via radio to a central site where the data are archived andor initially processed Modern radio-transmission methods usually use spread spectrum radios in the 900 MHz to 1 GHz plus band These radios do not require special licenses and can be deployed almost anywhere The downside to these radios is that the transmission paths must be ldquoline of sightrdquo thus all of the stations must be able to be ldquoseenrdquo by the central stations Repeaters can be used but this of course increases the cost
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-7
SECTION FOUR Step 4 Collection of Seismicity Data
Several commercial vendors can supply all of the necessary components An option becoming more attractive is cell phone technology however this requires cell phone access which in some remote areas is not possible or reliable Satellite transmission is possible but up load time are long with reasonably priced systems
A key issue when locating stations is land-ownership Surface stations are minimally invasive and permitting on public lands is usually easy If borehole stations are being used on public lands (BLM US Forest Service [USFS] etc) time should be allowed for some lengthy permitting processes (up to months) Even if the permittingland ownership issues are solved the actual topography and access may not permit ideal location of the stations As noted above real-time telemetry is important so it may not be possible to have line-of-sight (or even relay) stations everywhere where needed Usually however with enough forethought and planning most issues can be solved As noted above the aperture of the array of stations will depend on the number of EGS wells their spacing and depths Good depth control of the event locations will be necessary (+- 500 m accuracy or less) as well as east-west control (100 m accuracy or less)
Figure 4-3 Radio Transmission Equipment and Solar Panel at a Typical Seismic Station
All of this information is important for achieving a successful EGS project To date most EGS projects use a mixed array of borehole and surface stations which surround the injection point with an aperture large enough to locate events (with the desired accuracy as pointed out above) of the anticipated radius of influence (see Steps 1 and 5) Theoretically four data points (stations) are sufficient to locate an event assuming that these stations reasonably surround the event and assuming an accurate velocity model However owing to both heterogeneity and errors in ldquopickingrdquo the arrival times of the events (P and S waves) rarely can adequate locations of the events be determined with only four recording stations (although it is possible with both good P and S readings) Therefore usually 8 to 10 stations are needed to surround and cover the EGS project area down to small magnitude events (M -1 or less) (Figure 4-2) Note that the area
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-8
SECTION FOUR Step 4 Collection of Seismicity Data
of seismicity will grow over time this must be accounted for in station coverage and layout Accurate velocity models (3-D) are also needed to correct for wave path effects as well as any temporal changes in velocity structure as the reservoir evolves Note also that as the EGS operation proceeds it may be necessary to add andor move stations to adequately cover the seismicity Finally it is important to calibrate the sensors and array before operation begins Needed is the polarity of the sensors ( ie is up motion on the recorded data up ground motion is up east on the east-west horizontal is up on the north-south horizontal north etc) Very careful tracing of the signals (from the ground all the way through the system to the final seismogram) is necessary This can be done with a known source (explosion that records well all first motions at each station) side-by-side comparisons of all stations before deployment recording a large regional event with known ground motions etc) This is necessary for accurate focal mechanisms and moment tensor solutions In addition if possible calibration shots (deep sources where the location of the shot (preferably at the reservoir level) can be used for first motion detection as well as obtaining velocity models to be used in event locations Although this sounds simple in theory local geologic complexity and heterogeneity often complicate data interpretation
434 Data Archiving and Processing Requirements Once data collection starts the usual procedure is to collect the data at a central point and have software in place to detect events of interest For regulatory compliance operational understanding and public communication real time analysis will be needed The order and timing of processing may be different before the main EGS injection begins versus after the injection has begun In either case it will be necessary to have initial real-time locations and magnitudes of events posted to a publicly available web site This can be accomplished with available commercial software that can be customized for any site A variety of commercial products are in place to do so but usually the application must be customized for the particular site depending on the amount and magnitude range of the seismicity These commercial packages which are often sold with the microearthquake recording hardware usually offer such capability as automatic real-time detection of the events (based on user-specified criteria such as number of individual triggers which are in turn based on signal-to-noise ratio and the frequency content of each signal at each individual station in a specified time window) Once an event is detected a pre-specified time window of all channels of data (usually based on size of the detected event) is saved for processing either in real time with automatic picking or at a later time by a person who ldquohand picksrdquo the events In either case it is important to save the total waveforms of all channels of data from each event In most cases the data are continuously coming into a central collection point Consequently it is possible with todayrsquos large memory disks (terabytes of storage are very affordable) to not only store the automatically detected events but also to store all of the continuous data for later analysis This would allow going back and sifting through all of the data to see if any events were missed While such effort may not be necessary if hundreds of events are being detected it may be worthwhile especially in some areas of low seismicity to have all of the continuous data
Depending on the location of the project and collaborators with public entities it may be possible to interest such organizations as the USGS and IRIS to archive the data at reasonable costs A
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-9
SECTION FOUR Step 4 Collection of Seismicity Data
certain amount of processing is also available from these organizations if the data are of high quality
With good waveform data in hand there are a variety of options and ways to process the data The objective in this document is not to give an entire summary of earthquake analysis (books have been written about it [Aki and Richards 2009] but to point out basic needs and sources of information (It is assumed that the operators who need to understand the microearthquake data will have access to an experienced seismologist) The minimal needs are accurate locations especially depths times magnitude determinations and some source mechanism information Location programs are commercially available (using both P and S wave data) that use either 1-D or 3-D models these are usually least-squared types of solutions and sometimes cubic spline models The challenge in using 3-D location programs is to derive accurate 3-D velocity models The usual practice is to use the seismicity to invert for 3-D velocity structure and location together using tomographic inversion methods (Tomo 3-D is one such program in use) Programs incorporating anisotropy are being developed but are not available yet the drawback to these programs versus location programs such as the USGS Hypoinverse and various versions is the amount of data required to derive an accurate model with adequate resolution These programs need many seismic events that are distributed throughout the volume of interest That is many ray paths are needed to image the volume in enough detail to derive an accurate velocity model In tomography the pixel size is determined by how many ray paths penetrate each pixel The more ray paths the smaller the pixels can be The more complex the geologic structure the smaller the pixels need to be One way to address resolution and precision issues is to use differencing methods with either 1-D or 3-D velocity models ie ldquodouble differencerdquo methods This technique cancels out the ray path differences by using events close to one another (common stations for close events) which largely removes the path effects The double-difference (DD) earthquake location method was developed to relocate seismic events in the presence of measurement errors and earth model uncertainty (See httpwwwldeocolumbiaedu~felixwDDhtml [Waldhauser F and WL Ellsworth 2000] [Waldhauser F 2001] [Prejean St WL Ellsworth M Zoback and F Waldhauser 2002]) The method is an iterative least-squares procedure that relates the residual between the observed and predicted phase travel-time difference for pairs of earthquakes observed at common stations to changes in the ray path connecting their hypocenters through the change of the travel times for each event with respect to the unknown When the earthquake location problem is linearized using the double-difference equations the common mode errors cancel principally those related to the receiver-side structure Thus avoided is the need for station corrections or high-accuracy of predicted travel times for the portion of the ray path that lies outside the focal volume This approach is especially useful in regions with a dense distribution of seismicity ie where distances between neighboring events are only a few kilometers or less But there must be enough events close together to do this (USGS uses a combination of both ie Tomo DD) Magnitude determination is not straightforward for smaller events (see httpvulcanwrusgsgovGlossarySeismicitydescription_earthquakeshtml and httpwwwseisutaheduEQCENTERLISTINGSmagsumhtm) One approach is to take the spectra of events and filter to simulate as if the data were recorded on a Wood-Anderson instrument and determine the Richter magnitude but this is not often done Sometimes coda
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-10
SECTION FOUR Step 4 Collection of Seismicity Data
magnitudes are used based on empirical data for each region using larger events and extrapolating to smaller events
What is more common and more reliable is using moment magnitude (M) However proper instrumentation is required to capture the low frequency level of the event which may not be possible if high frequency geophones are used It is derived by taking the waveform data into the frequency domain and correcting for instrument response such that the displacement spectra are obtained From the DC level of the spectra the moment can be derived and a moment magnitude determined using empirical formulas One such formula is M = 23 log10(Mo) - 107 (Hanks and Kanamori 1979) (Mo = seismic moment in dyne-cm) The moment magnitude relation may also be different for different region and should be calibrated for each area
Source-mechanism studies are important but as mentioned before routine moment tensor calculations are difficult using high-frequency arrays that typically cover only part of the total radiation pattern of an earthquake In addition at higher frequencies usually recorded with smaller events the earth structure has a larger effect on wave paths Thus it is more difficult to obtain reliable moment tensor solutions If moment tensor solutions are desired (they are important for gaining an understanding of the failure mechanisms associated with the reservoir creation process) it will be necessary to set out instrumentation that can record the low-frequency component of the seismic waveforms as well as having a detailed velocity model of the geology
44 SUMMARY Gathering the correct seismic array data is essential at all stages of the EGS project This will allow a variety of processing to be done both in real time and after data have been collected There are a few reasons for properly collecting seismic data achieving public acceptance performing risk assessment and monitoringunderstanding the EGS reservoir Accurate real time data are necessary for all of those reasons The detail and amount of data will depend on site conditions and the EGS reservoir characteristics and the proximity to populated communities and the anticipated risk and hazards
45 SUGGESTED READING Lee WHK and Stewart SW 1981 Principles and applications of microearthquake networks
Academic Press 293 p
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 4-11
5 Section 5 FIVE Step 5 Hazard Evaluation of Natural and Induced Seismic Events
SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
51 PURPOSE The purpose of Step 5 is to estimate the ground shaking hazard at a proposed EGS site due to natural (tectonic) seismicity and induced seismicity Assessing the ground shaking hazard from natural seismicity will provide a baseline from which to evaluate the additional hazard from induced seismicity This is a critical step to assessing the probability of exceeding the criteria specified in Step 3 Hazard is defined as the effect of a physical phenomenon (such as an earthquake or induced seismic event) that will result in an unacceptable consequence (damage loss annoyance etc) Structural (non-cosmetic) damage can only result when a structure undergoes several cycles of ground shaking The resulting seismic loading induces strains in the structure resulting in failure of structural components No cases are known to date where geothermal-induced seismicity has caused structural (non-cosmetic) damage (see definition) because in general the seismic events are of small magnitude (lt M 40) However because the potential may exist given some specific circumstances hazard analyses need to be performed An earthquake can present several types of hazards however for induced seismic events we are primarily concerned with ground shaking Once the ground shaking hazard is quantified associated secondary hazards such as liquefaction and slope failure (eg landsliding) can be evaluated Step 5 should be performed before any geothermal stimulations and operations are initiated Characterization of future induced seismicity at a site is a very complex and difficult problem thus assessments must be based on case histories and numerical modeling that incorporates specific site characteristics The hazard analyses should be updated once data and information on the EGS seismicity become available
Two approaches can be taken to assess the ground shaking hazard at a proposed site a probabilistic seismic hazard analysis (PSHA) and a deterministic seismic hazard analysis (DSHA) Hazard results feed into risk analysis as described in Section 6 Probabilistic hazard is more useful for risk analysis because it provides the probabilities of specified levels of ground motions being exceeded Scenario-based risk analysis using the results of DSHA is useful to describe potential maximum effects to stakeholders
Several physical factors control the level and character of earthquake ground shaking These factors are in general (1) rupture dimensions geometry orientation rupture type and stress drop of the causative fault (2) distance from the causative fault (3) magnitude of the earthquake (4) the rate of attenuation of the seismic waves along the propagation path from the source to site and (5) site factors including the effects of near-surface geology particularly from soils and unconsolidated sediments Other factors which vary in their significance depending on specific conditions include slip distribution along the fault rupture directivity footwallhanging-wall effects and the effects of crustal structure such as basin effects
The ground motion hazard should be expressed in terms of peak ground acceleration (PGA) acceleration response spectra (to compare with spectra from natural earthquakes and building code design spectra) peak ground velocity (PGV) and velocity spectra PGV (or PPV) will be needed for comparison with cosmetic and structural building damage criteria with criteria for vibration sensitive research and manufacturing facilities and for human activity interference
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
52 OVERVIEW OF APPROACH PSHAs should be performed first for the natural seismicity and then for the EGS-induced seismicity (an addition to the natural hazard) As discussed in Section 1 the hazard from natural seismicity for sites in the US can be obtained from the USGS National Seismic Hazard Maps However the hazard estimates from the USGS maps are not site-specific Because a comparison of the hazard from natural and induced seismicity is required site-specific analyses are needed at this stage The PSHA methodology and each step in the hazard evaluation process are described in detail in the next sections DSHAs can be performed for additional insight into the seismic hazard
521 Estimate the Baseline Hazard from Natural Seismicity The major steps to be performed to evaluate the baseline hazard from natural seismicity are
1 Evaluate the historical seismicity in the site region and calculate the frequency of occurrence of background seismicity based on the earthquake catalog If baseline seismic monitoring was performed in the EGS geothermal project area that data should be incorporated into the earthquake catalog
2 Characterize any active or potentially active faults in the site region and estimate their source parameters (source geometry and orientation rupture process maximum magnitude recurrence model and rate) for input into the hazard analysis
3 For communities that may be impacted by future EGS-induced seismicity evaluate the geological site conditions beneath the communities and if practical estimate the shear-wave velocities of the shallow subsurface
4 Select appropriate ground motion prediction models for tectonic earthquakes for input into the hazard analysis
5 Perform a PSHA and produce hazard curves and hazard maps if required to assess the baseline hazard due to natural seismicity before any induced seismicity occurs
522 Estimate the Hazard from Induced Seismicity For comparison to natural seismicity estimating the hazard from EGS-induced seismicity particularly before EGS operations are initiated is more difficult The database of induced seismicity observations in terms of both seismic source characterization and ground motion prediction is also much smaller than for natural seismicity However as more information becomes available (particularly seismic monitoring results) the hazard can be updated and the uncertainties in the hazard results reduced Possible steps that should be taken include
1 Evaluate and characterize the tectonic stress field based on focal mechanisms of natural earthquakes the geologic framework of the potential geothermal area and any other available data particularly the results from any prior seismic monitoring
2 Review known cases of induced seismicity and compare the tectonic and geologic framework from those cases with the potential EGS area
3 Evaluate the characteristics and distribution of pre-existing faults and fractures This characterization will be useful in assessing the potential and characteristics of future EGS-induced seismicity as related to the tectonic stress field
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
4 Review and evaluate available models for induced seismicity that estimate the maximum magnitude of induced seismicity based on injection parameters
5 Review and select empirical ground motion prediction model(s) appropriate for induced seismicity if any are available or at a minimum one that is appropriate for small to moderate magnitude natural earthquakes (moment magnitude [M] lt 50)
6 Perform a PSHA and produce hazard curves and hazard maps if required to assess the EGS-induced seismicity hazard
7 An optional step is to calculate scenario ground motions from the maximum induced seismic event by performing a DSHA
53 PSHA METHODOLOGY AND COMPUTER PROGRAMS The objectives in a PSHA are to evaluate and characterize potential seismic sources the likelihood of earthquakes of various magnitudes occurring on or within those sources and the likelihood of the earthquakes producing ground motions over a specified level (Figure 5-1) The PSHA methodology allows for the explicit inclusion of the range of possible interpretations in components of the seismic hazard model including seismic source characterization and ground motion estimation Uncertainties in models and parameters can be incorporated into the PSHA through the use of logic trees
The PSHA methodology is based on the model developed principally by Cornell (1968) The occurrence of earthquakes on a fault is assumed to be a Poisson process The Poisson model is widely used and is a reasonable assumption in regions where data are sufficient to provide only an estimate of average recurrence rate (Cornell 1968) The occurrence of ground motions at the site in excess of a specified level is also a Poisson process if (1) the occurrence of earthquakes is a Poisson process and (2) the probability that any one event will result in ground motions at the site in excess of a specified level is independent of the occurrence of other events There are publically available computer programs that can be used to perform a PSHA We recommend the two most available programs that have been validated in the Pacific Earthquake Engineering Research (PEER) Center-sponsored Validation of PSHA Computer Programs Project (Thomas et al 2010) They include the HAZ program developed by Norm Abrahamson which is available from the author upon request and EZ-FRISK which can be obtained through license from Risk Engineering Inc The following describes in more detail the steps to perform a PSHA for natural seismicity outlined in Section 621
531 Evaluate Historical Seismicity In Step 4 a historical earthquake catalog is compiled The value of evaluating the historical seismicity of the site region is two-fold (1) it can be used to characterize the natural seismicity and (2) it can provide some insight into the potential for induced seismicity Note there certainly are exceptions the most important being that induced seismicity can occur in regions with low historical seismicity
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
Figure 5-1 The Steps in Performing a PSHA
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
532 Characterize Seismic Sources Seismic source characterization is concerned with three fundamental elements (1) the identification location and geometry of significant sources of earthquakes (2) the maximum sizes of the earthquakes associated with these sources and (3) the rate at which the earthquakes occur Two types of earthquake sources are typically characterized in PSHAs (1) fault sources and (2) areal source zones Fault sources are modeled as three-dimensional fault surfaces and details of their behavior are incorporated into the source characterization Areal source zones are regions where earthquakes are assumed to occur randomly Uncertainties in the seismic source parameters can be incorporated into PSHA using a logic tree approach In this procedure values of the source parameters are represented by the branches of logic trees with weights that define the distribution of values A sample logic tree is shown in Figure 5-2
Figure 5-2 Seismic Hazard Model Logic Tree
In a PSHA earthquakes of a certain magnitude are assumed to occur randomly along the length of a given fault or segment (Figure 5-1) The distance from an earthquake to the site is dependent on the source geometry the size and shape of the rupture on the fault plane and the likelihood of the earthquake occurring at different points along the fault length The distance to the fault is
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
defined to be consistent with the specific ground motion prediction model used to calculate the ground motions The distance therefore is dependent on both the dip and depth of the fault plane and a separate distance function is calculated for each geometry and each ground motion prediction model The size and shape of the rupture on the fault plane are dependent on the magnitude of the earthquake larger events rupture over longer and wider portions of the fault plane Rupture dimensions are modeled following standard magnitude-rupture area and rupture-width relationships
5321 Fault Geometry
The first step in characterizing potential seismic sources is to identify which known faults are ldquoactiverdquo and hence seisenic seismogenic ie capable of producing earthquakes in the future The criteria for defining an active fault varies widely among US government regulatory agencies For example in California a fault that has moved in the past 35000 years is considered an ldquoactiverdquo fault A ldquoconditionally activerdquo fault is defined as a fault that has ruptured in Quaternary time (past 16 million years) but its displacement history is unknown in the past 35000 years The USGS maintains the Quaternary Fault and Fold Database that can be used to identify active faults during the Quaternary and included in the site-specific PSHA The database also contains many of the parameters such as fault location strike and dip that are needed although parameter uncertainties may not be included
For each active fault to be included in the hazard analysis the location and orientation (strike dip and dip direction) segmentation model thickness of the seismogenic zone style of faulting (strike-slip normal or reversethrust) are needed (Figure 5-3) This information can generally be adopted from the USGS database The top and bottom of each fault are also required If the fault is expressed at the surface the top is zero For buried faults an estimate must be made unless subsurface information is available such as seismic data The bottom of the fault can be estimated from the seismicity data which will delineate the bottom of the seismogenic crust usually 12 to 20 km in the western US If the fault is long greater than 60 to 80 km the fault may be segmented That is portions of the fault rather than the whole fault may rupture If such information exists from paleoseismic andor historical data the rupture segmentation model needs to be included in the PSHA
5322 Maximum Magnitude
The maximum earthquake that a fault or fault segment can generate is usually derived by the use of empirical relationships between magnitude and either rupture length or rupture area (rupture length times rupture width) unless the maximum earthquake has been observed historically There are other approaches but the use of rupture dimensions is most common The most commonly used set of empirical relationships are by Wells and Coppersmith (1994) For example based on rupture length a 40 km-long fault can generate a M 69 earthquake based on Wells and Coppersmith (1994) The USGS Fault and Fold Database also provides values of maximum magnitude although uncertainties are not included
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
Source Brumbaugh 1999
Figure 5-3 The three principal types of faults (a) strike-slip faults (b) reverse faults and (c) normal faults
5323 Recurrence Parameters
The recurrence parameters include recurrence model recurrence rate (slip rate or average recurrence interval for the maximum event) slope of the recurrence curve (b-value) and maximum magnitude The recurrence relationships for the faults are modeled using the truncated exponential characteristic earthquake and the maximum magnitude recurrence models (Figure 5-2) These models are generally weighted in a PSHA to represent onersquos judgment on their applicability to the sources For the areal source zones only an exponential recurrence relationship is assumed to be appropriate
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
The truncated exponential model is a form of the classical Gutenbeg-Richter model The model where faults rupture with a ldquocharacteristicrdquo magnitude on specific segments is described by Schwartz and Coppersmith (1984) The characteristic model often used in PSHAs is the numerical model of Youngs and Coppersmith (1985)
The maximum magnitude (or moment) model can be regarded as an extreme version of the characteristic model (Wesnousky 1986) In the maximum magnitude model there is no exponential portion of the recurrence curve ie events are modeled with a normal distribution about the characteristic magnitude
The average recurrence interval for the characteristic or maximum magnitude event defines the high magnitude (low likelihood) end of the recurrence curve When combined with the relative frequency of different magnitude events from the recurrence model the recurrence curve is established
5324 Recurrence Rates
The recurrence rates for the fault sources are defined either by the slip rate or by the average recurrence interval for the maximum or characteristic event and the recurrence b-value An example of recurrence intervals sometimes referred to as inter-event times would be the approximately 300-year interval of the North Coast segment of the San Andreas fault which ruptured in the Great 1906 M 78 San Francisco California earthquake Slip rate is defined as fault displacement divided by the time period in which displacement occurred Slip rate is a proxy for activity rate Recurrence interval is the time period between individual earthquakes (The North Coast segment of the San Andreas fault has a slip rate of about 20 mmyr)
533 Areal Sources Areal sources are usually used to account for ldquobackgroundrdquo earthquakes The hazard from background (floating or random) earthquakes that are not associated with known or mapped faults must be incorporated into the hazard analysis In most of the western US the maximum magnitude for earthquakes not associated with known faults usually ranges from M 6 to 7 Repeated events larger than these magnitudes probably produce recognizable fault-or fold-related features at the earthrsquos surface For areal source zones only the areas maximum magnitude and recurrence parameters (based on the historical earthquake record) need to be defined
534 Characterize Site Conditions The geologic conditions beneath a site can significantly influence the level and nature of ground shaking In very general terms soil sites will have a higher level of ground motions than rock sites due to site amplification Hence to be able to predict the ground shaking at a site particularly a soil site the underlying shear-wave velocity (VS) structure is needed to a depth of at least 30 m and deeper if possible The parameter VS30 (the average VS in the top 30 m) is used in ground motion prediction models and in the US building code (called the International Building Code or IBC) to classify different site conditions For example the NEHRP site classification has six site classes hard rock rock very dense soil and soft rock stiff soil soft soil and soft liquefiable soil The VS profile (VS versus depth) is often used in ground motion prediction models to quantify site and building foundation responses The VS profile at a site can
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
be obtained through geophysical surveys such as downhole and crosshole surveys surface wave techniques and microtremor surveys
535 Select Ground Motion Prediction Models To characterize the ground motions at a specified site as a result of the seismic sources considered in the PSHA and DSHA ground motion prediction models for spectral accelerations are used These models are generally based on strong motion data and relate a specified ground motion parameter (eg PGA) with the magnitude and distance of the causative event and the specific site conditions at the potentially affected site(s) Examples of ground motion prediction models are the recently developed Next Generation of Attenuation (NGA) models developed by the Pacific Earthquake Engineering Research Center (Figure 5-4) These models are appropriate for earthquakes of M 50 and greater A model by Chiou and Youngs (2010) was developed for earthquakes of M 30 to 55
The uncertainty in ground motion models is included in the PSHA by using the log-normal distribution about the median values as defined by the standard error associated with each ground motion prediction model
Source Abrahamson et al 2008
Figure 5-4 Comparison of Distance Scaling of PGA for Strike-Slip Earthquakes for VS30 760 msec
536 PSHA Products The primary products of a PSHA are hazard curves that show the annual frequency of exceedance for some specified ground motion parameter (eg PGA Figure 5-5) Often the term ldquoreturn periodrdquo which is the inverse of the annual frequency of exceedance is used The IBC uses an annual frequency of exceedance of 1 in 2475 or a return period of 2475 years The
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
results of a PSHA can also be deaggregated to evaluate what seismic sources are contributing most of the hazard at a site
Figure 5-5 Seismic Hazard Curves for Peak Horizontal Acceleration
54 ADDITIONAL STEPS IN CHARACTERIZING EGS FOR PSHA In typical PSHAs for engineering design the minimum magnitude considered is M 50 because empirical data suggests that smaller events seldom cause structural damage (Bommer et al 2006) Since no EGS-induced earthquake has exceeded M 50 in size to date the hazard analyses should be performed at lower minimum magnitudes We suggest that PSHAs be performed for M 40 so that the hazard with EGS seismicity can be compared with the baseline hazard from tectonic earthquakes To provide input into the risk analysis (Step 6) an even lower minimum magnitude may be considered for nuisance effects or interference with sensitive activities
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
541 Characterize Local and Regional Stress Field Most induced seismic events will occur on pre-existing zones of weakness eg faults and fractures that are favorably oriented to the tectonic stress field Knowledge of the local and regional stress field can thus help identify a priori which features are more likely to be the sources of induced seismicity The characterization of the stress field can be obtained from in situ stress measurements (eg hydraulic fracturing borehole breakouts and core-induced fractures) The orientations and magnitudes of the maximum intermediate and minimum principal stresses are required A combination of image log analysis and a diagnostic hydraulic fracturing (extended leak-off test or ldquominifracrdquo) is the best approach for measuring in situ stresses With knowledge of the in situ stress field a Mohr-Coulomb stress analysis can be performed to assess the critical stress required to trigger slip on favorably-oriented faults that are critically stressed and near failure
Earthquake focal mechanisms can provide information on the principal stresses but not their absolute magnitudes Stress fields can be categorized by which style of faulting will be dominant strike-slip normal (extensional) and reversethrust (compressional) (Figure 5-2)
542 Develop 3D Geologic Model To the extent practicable and given the available data a 3D structural and stratigraphic model of the EGS area should be developed that includes pre-existing faults and fractures that could be sources of future induced seismicity Characterizing any significant favorably oriented fault is critical for assessing the maximum earthquake that could occur (see below) Often 2-D and 3-D models are developed to evaluate the EGS potential of an area in the early stages of a project This should include evaluations of drilling results wellbore image logs seismic reflection data and any other subsurface imaging data that may exist (eg seismic tomography potential field data etc)
543 Review of Relevant EGS Case Histories In particular the information on the maximum magnitude and the frequencies of occurrence of case histories of induced seismicity should be reviewed Numerous publications are available that describe cases of EGS and geothermal-induced seismicity Majer et al (2007) summarizes some of the most significant case histories Geothermal-induced seismicity has occurred in several countries including most notably the US Japan Australia France and Switzerland
544 Develop Induced Seismicity Model Developing a model for induced seismicity is the most challenging task in assessing the hazard Induced seismicity is the interaction between the injection parameters such as injection rates pressures and volume and depth of injection and the in situ lithologic structural hydrologic and thermal conditions (eg faults fractures rock strength porosity permeability etc) These are the most challenging geologic characteristics to evaluate because of the difficulty in imaging and the general heterogeneity and complexity inherent in rock masses Given this challenge conservative assumptions on the maximum induced event and rates of induced seismicity can be made for upper-bound estimates of the hazard Best estimates of the hazard can be improved by incorporating the possible ranges of parameters and their uncertainties In some circumstances an evaluation of the potential for far-field triggering of a damaging earthquake on a nearby fault
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
due to fluid-injection induced seismicity may be required although no such cases have been observed to date
Maximum magnitudes and earthquake rates are the two most important inputs into seismic hazard analyses The magnitude of an earthquake is proportional to the area of the fault that slips in an event and the amount of that slip Several conditions must be met for a large and potentially damaging earthquake to occur There must be a large enough fault stresses must be high enough to cause slip and the fault needs to be pre-stressed and near failure Predicting the maximum magnitudes of earthquakes due to EGS activities has been a difficult challenge As recognized by many the characteristics of induced seismicity are controlled by the nature and distribution of pre-existing fractures and faults the local stress field in the volume of rock surrounding the well where fluid is being introduced (eg Majer et al 2007) and the characteristics of the pore pressure field due to injection Empirical relationships have been developed that estimate the magnitude of an earthquake from rupture length rupture area and maximum and average event displacement The best approach to estimating the potential maximum induced earthquake is to characterize the maximum dimensions of pre-existing faults that could rupture in an induced earthquake To be able to estimate fault dimensions imaging faults in the subsurface is required A number of theoretical approaches have been developed to predict maximum magnitude All the approaches above depend on an a priori knowledge of the rupture characteristics of future induced seismicity which requires subsurface characterization of the affected volume of rock around the well McGarr (1976) relates the sums of the seismic moment released in earthquakes to a change in volume In the case of fluid injection this change is the volume added to the system by injection A second approach is to relate the seismic moment or maximum magnitude to the maximum length or area of pre-existing faults in the volume of rock that will be affected by fluid injection A third approach has been proposed by Shapiro et al (2010) using the parameter ldquoseismogenic indexrdquo Shapiro et al (2007) observed that under ldquogeneral conditionsrdquo the number of fluid-induced earthquakes with a magnitude larger than a given value increases approximately proportionally to the injected fluid volume The seismogenic index depends on the local maximum critical pressure for shear fracturing the volume concentration of pre-existing fractures and the poroelastic uniaxial storage coefficient (Shapiro et al 2010) Along with the injection parameters the seismogenic index can be used to estimate the probability of a given number of such events during an injection period Shapiro et al (2010) applied this technique for six case studies of injection induced seismicity including Cooper Basin Basel and Ogachi
Estimating the rate of EGS seismicity a priori is a significant challenge because the problem is very site-specific and not all factors that can impact rate are quantifiable at this time However efforts are underway in the US and Europe where induced seismicity is an important issue (eg Basel) to develop probabilistic approaches to estimating ground motions in near-real time for alarm systems A traffic-light alarm system which is based on public response magnitude and PGV has been used in experiments such as Basel (Section 7) For example Bachmann et al (2011) are developing a forecast model by modeling the Basel sequence and testing various statistical models such as the aftershock model for California earthquakes The intent is to translate the forecast model to probabilistic hazard eg probability for exceeding a ground motion level
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SECTION FIVEStep 5 Hazard Evaluation of Natural and Induced Seismic Events
545 Select Ground Motion Prediction Models for Induced Seismicity Almost all existing ground motion prediction models have been developed for M 50 and above natural earthquakes and it has been suggested that there is a break in scaling between small and large earthquakes (Chiou et al 2010) To our knowledge no ground motion prediction model for EGS seismicity or geothermal-induced seismicity has been developed and made publically available In lieu of a model for induced seismicity the model proposed by Chiou et al (2010) for small to moderate natural earthquakes (M 3 to 55) in California is the next best alternative Ground motion models for earthquakes smaller than M 5 are being developed by PEER and should be available in 2013 Since the maximum induced earthquake will likely be smaller than M 50 the ground motion prediction model only needs to be accurate at short distances (less than 20 km
546 Products The products of a PSHA are the same as described in Section 536 the only difference being is the results will now include potential induced seismicity in addition to background tectonic seismicity
55 SUMMARY The hazard results from the natural and induced earthquakes should be compared to assess the potential increase in hazard associated with the EGS project The hazard results are fed into Step 6 the risk analysis The hazard estimates should be updated as new information becomes available after injection activities have commenced and if and when induced seismicity has been initiated In particular the results of the seismic monitoring should be evaluated and incorporated into the hazard analyses where possible
56 SUGGESTED READING McGuire RK 2004 Seismic hazard and risk analysis Earthquake Engineering Research
Institute MNO-10 221 p
Reiter L 1990 Earthquake hazard analysis issues and insights Columbia University Press New York 254 p
Yeats RS Sieh K and Allen CR 1997 The geology of earthquakes Oxford University Press 568 p
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 5-13
6 Section 6 SIX Step 6 Risk Informed Decision Analysis and Tools for Design and Operation of EGS
SECTION SIX Step 6 Risk Informed Decision Analysis and Tools for Design and Operation of EGS
61 PURPOSE The purpose of this step is to give guidance for performing a risk analysis whose results will help make decisions with the intent of minimizing the risk of damage annoyance or losses that the design and operation of an EGS project might produce and possibly to maximize the benefits to the operators and to local communities The detailed risk analysis needs to be time-dependent because the stress conditions in the EGS field will change in relation to the injection schedule The risk profile will change accordingly and finally return to the natural seismicity risk after all the stress perturbations caused by the EGS operation in and around the EGS field have dissipated which could take several decades after stopping injection
62 OVERVIEW OF BEST PRACTICE APPROACH Formal seismic risk analysis started in the mid 20th century to analyze the design of complex systems and in the 1970s it developed considerably in its application to the nuclear industry It is now a mature field that is routinely used with geographic information systems to analyze projects at the community state or regional level Seismic risk analysis is a well-accepted approach and its methods and tools are extensively used by local and regional governments and by the insurance industry to predict possible losses from natural catastrophes and to help decide on such things as premiums fees and compensation
621 Hazard Vulnerability and Exposure Seismic risk is usually expressed as a probability of all the relevant adverse impacts of the ground shaking occurring For EGS projects we are concerned with the impact of the seismicity induced by the EGS operation which if it does not have all the attributes of the standard type of analysis performed for natural catastrophes still possesses some of its most important elements Some of the effects of the seismic ground shaking are in the form of ldquophysicalrdquo consequences such as structural damage to houses and other engineered structures or to the physical environment There is also ldquonon-physicalrdquo damage to humans physiological and psychological in nature For example peoplersquos sleep can be disturbed or they can develop anxieties from the frequent occurrence of small earthquakes that are otherwise physically non-damaging Much of this anxiety is caused by concern over property and homes even if the ground motion is insufficient to cause structural or cosmetic damage
As described in Section 5 the seismic hazard that is of importance here is the ground shaking that is produced at a location by the occurrence of an earthquake and seismic hazard analysis describes the potential for this ground shaking It is expressed by a probability distribution of the selected ground shaking parameter (eg PGA PGV andor response spectra)
Vulnerability describes how the component of a system can fail or lose its function For a building or an engineered facility it describes probabilistically the state or level of damage that it will be in after being subjected to a seismic ground shaking (eg four possible states of damage V-L L M and H) It is expressed as a probability of being in a given state of damage for a given level of ground shaking
BEST PRACTICES EGS INDUCED SEISMICITY 8-APRIL-2016 6-1
