Earthquake early warning for Israel: Recommended … · 2014-05-11 · Earthquake early warning for...

1

GII 500/676/12

Earthquake early warning for Israel:

Recommended implementation strategy

Richard M. Allen (Chair)1, Gidon Baer (Coordinator) 2,4,

John Clinton3, Yariv Hamiel4, Rami Hofstetter5,

Vladimir Pinsky5, Alon Ziv6, Aldo Zollo7

1 - University of California, Berkeley, USA

2 - Earth and Marine Research Administration, Israel

3 - ETH Zurich, Switzerland

4 - Geological Survey of Israel

5 - Geophysical Institute of Israel

6 - Tel Aviv University, Israel

7 - University of Naples "Federico II", Italy

International advisory committee on earthquake early warning

GSI/26/2012 GII 500/676/12

Jerusalem, December 2012

Ministry of Energy and Water Resources

Geological Survey of Israel

The Geophysical Institute of Israel

2

Table of Contents

Executive summary ................................................................................................................................ 3

Committee charge ................................................................................................................................... 5

Tectonic setting and seismic risk ...................................................................................................... 6

Guiding principles for the development of a warning system ............................................. 10

Approaches to early warning ........................................................................................................... 11

Regional EEWS ....................................................................................................................................... 13

Onsite EEWS ........................................................................................................................................... 14

Front detection or barrier EEWS (S-wave threshold EWS) ................................................... 15

The proposed Early Warning system for Israel ......................................................................... 16

Simulated early warning performance in Israel ....................................................................... 20

Assessment of alert times .................................................................................................................. 20

Simulations of P-wave approach .................................................................................................... 25

Recommendations for software implementation .................................................................... 29

Recommendations for early-warning capable network stations ....................................... 30

Proposed initial design ...................................................................................................................... 32

Timeline and budget for implementation ................................................................................... 36

Timeline ................................................................................................................................................... 36

Estimated budget .................................................................................................................................. 39

Important improvements beyond the initial 2-year plan ..................................................... 40

Building seismological capacity in Israel .................................................................................... 42

Bibliography ........................................................................................................................................... 43

3

Executive summary

The purpose of this report is to recommend an optimal design and implementation plan

for an earthquake early warning system in Israel. The goal of the project is to provide

earthquake warning to schools around the nation within 2 years of project

commencement, and extend the warning nationwide beyond a period of 3 years. This

recommendation was prepared by an international advisory committee on Earthquake

Early Warning that was formed by the Earth and Marine Research Administration (EMRA),

Ministry of Energy and Water Resources of Israel and assembled in Jerusalem from

September 9th to 14th, 2012. The committee consisted of eight: Prof. Richard M Allen

(committee chair), Director of the seismological laboratory, University of California,

Berkeley, USA; Dr. John Clinton, Director of seismic networks, Swiss Seismological Service,

ETH, Zurich, Switzerland, Prof. Aldo Zollo, Seismologist,University of Naples "Federico II",

Italy; Dr. Gidon Baer (committee coordinator), acting General Director of the EMRA, Dr.

Yariv Hamiel, Geophysicist, Geological Survey of Israel; Dr. Rami Hofstetter and Dr.

Vladimir Pinsky, Seismologists, the Geophysical Institute of Israel, and Dr. Alon Ziv,

Seismologist, Tel Aviv University.

The infrastructure for providing earthquake early warning in Israel will be a state-of-the-

art seismic network that will provide the best possible early warning capability for the

entire state of Israel and its entire population, within the proposed budget and timeline,

while also allowing for improvements in the warning system as warning algorithms

continue to be developed and enhanced around the world. This new seismic system

should build on the existing monitoring capability in Israel in order to maximize the long-

term operability of the system. Specifically, the new seismic network stations that we

propose should be integrated into the Israeli Seismic Network (ISN), and the ISN should be

simultaneously upgraded.

There are two types of approach to earthquake early warning. The first is an S-wave

based threshold approach, which alerts when two or more seismic stations observe

ground shaking above a pre-defined strong shaking level. The advantage of this approach

is simplicity and that cheap low-quality accelerometers can be used. The challenges

include the fact that the first earthquake to trigger the system will be the big earthquake

for which an alert is needed so without lowering the threshold – often not possible for

low-quality sensors, only simulated testing is possible; alerts are only generated for events

close to the sensors; and there is currently no open source community supported

4

processing system. These challenges all mean that there is no possibility of upgrade or

improvements to the system in the future without a significant investment.

The second approach is the P-wave based earthquake detection. This approach uses P-

waves—which travel about twice as fast as S-waves and cause little damage—to detect

earthquakes, characterize the source magnitude and location, and then issue an alert

based on predicted shaking. The approach requires higher quality equipment, but it

allows for location specific alerts (a dynamic grid approach) and regular testing through

detection of smaller (non-hazardous) earthquakes. This is the approach favored by early

warning groups around the world (e.g., Japan, Taiwan, California, Italy, Switzerland). For

this approach there is also an open source community supported software.

The committee recommends a hybrid approach for Israel that invests in the necessary

hardware for a P-wave based system, while also supporting an initial S-wave based

threshold approach which can be implemented very rapidly at little additional cost. We

propose the installation of high quality seismic instrumentation along the Dead Sea and

Carmel Faults, consisting of a mixture of accelerometers and broadband velocity

instruments. These new seismic sites should be integrated into the ISN, and existing ISN

stations should be upgraded to the same quality. Seismic network management software

should be installed at a hub at the Seismology Division where an open source community

supported earthquake monitoring system will collect data from all seismic sites and

perform real-time event characterization and alerting. A secondary back-up seismic

network hub should be installed at a geographically separate location after the evaluation

period of the system. We recommend to initially implementing an S-wave based threshold

algorithm which can be put into action within the tight timeline decided by the Israeli

Government. A P-wave based approach should then be added, and an initial version is

expected to be ready within two years. Further assessment of system performance should

continue beyond this period in order to improve and optimize the algorithms making full

use of advances made by the early warning community around the world.

The proposed seismic network to be installed is as follows (see Fig. 8). A total number of

49 accelerometer-only sites will be deployed close to the Dead Sea and Carmel Faults

(within 15 km) in a single array of stations every ~10 km, south of the Dead Sea, and in a

staggered geometry (two parallel echeloned arrays of stations ~10 km apart) from the

Dead Sea northward. Five additional sites with co-located seismometers and

accelerometers should be deployed at large spacing along the Dead Sea Fault.

5

Recommended specifications for all the instrumentation is provided in this report. This

plan fits within the approved budget and timeline.

The committee also recommends some additional areas of development and network

improvements that do not fit into the initial two-year plan, but are believed to be

important and should be pursued once the initial system as described above has been

installed and is operating. These include densification of the network (if required),

construction of a secondary backup hub, the development of a user base beyond just

schools; the continued development of improved early warning algorithms for Israel; the

implementation of an onsite approach for schools; continued evaluation of system

performance (based on small earthquakes and system test events); an evaluation of

system robustness for redundancy and performance; development of other real-time

earthquake information products including ShakeMaps; and the possible inclusion of real-

time GPS.

Finally, it is critical that an effort is made to build seismological capacity in Israel. Success

with early warning requires ongoing and continuous efforts in both academic and applied

research that is occurring in the university and governmental earth science research

institutes. The new seismic network will provide a significant amount of geophysical data

that should be effectively mined to improve understanding of seismic hazard and

seismotectonics. This includes ground motion attenuation relations, site effects, fault

mapping and delineation using microseismicity, and probabilistic seismic hazard

assessment. In order to support the successful operation and development of the early

warning system the next generation of seismologists in Israel must also be educated,

supported, developed and trained. This must start with the encouragement of students in

seismology and continue with the development of fulfilling career paths for them in Israel.

To achieve this goal, mechanisms to encourage, promote and financially support exchange

of students, postdocs and experienced researchers from and to Israel for earthquake

research is necessary.

Committee charge

The principal objective of the committee is to recommend an optimal earthquake early

warning system for the State of Israel, which should meet high operational standards, will

be financially and technically feasible, and will be implemented within a two-year

timeframe. The committee is charged to propose the system’s geographical configuration,

6

its hardware, and software. Evaluation and recommendations regarding the benefits of the

system during its operation, both from the seismic hazard and the scientific aspects are

also included in the mandate of this committee.

Tectonic setting, seismic risk, and existing NETwork

The Dead Sea fault (DSF) poses a seismic threat to the population centers in its vicinity.

The fault system accommodates the left-lateral motion between the Sinai subplate and the

Arabian plate (Fig. 1). It is about 1,200 km long and connects the Taurus-Zagros

compressional front in the north, to the extensional zone of the Red Sea in the south. Over

the past few million years tectonic movements have shaped the Dead Sea Fault system.

The Dead Sea fault comprises several major basins connected by large faults. The Dead

Sea basin is the largest one. The total tectonic motion is primarily left-lateral strike-slip

and estimated to be approximately 5 mm per year.

Figure 1. General tectonic map of the region. The Dead Sea Fault and the Carmel Fault (labeled

CFS) are believed to be the primary sources of seismic hazard.

7

The Dead Sea Fault poses a major threat to the population of Israel, Jordan, Syria, Lebanon,

and the Palestinian Authority. Records of destructive earthquakes that occurred in the last

3,000 years—some of which were catastrophic—are mentioned in the Bible, in later books,

or as reports by pilgrims who came to the Holy Land. Some examples include: (1) The 31

BC catastrophic event as described by Josephus Flavius in Antiquities of the Jews. (2) The

so called Bet Shean earthquake of 18/1/749. (3) Several strong events in today’s northern

Israel and southern Lebanon in May 1202. (4) Two strong earthquakes in October and

December 1759. (5) A strong earthquake in January 1837. These devastating events

claimed up to 30,000 casualties, several tens of thousands of wounded people and a large

number of fully or partially destroyed buildings in various cities and villages over a large

area. We do not know the exact magnitudes of these events, however, based on various

indications they are estimated to be of M 7.0 and above.

Since the beginning of the 20th century, several moderate earthquakes occurred along the

Dead Sea Fault. The M 6.2 earthquake of July 11, 1927, resulted in 285 deaths, 940

wounded and extensive damage in many towns and villages on both sides of the Dead Sea

Fault. Throughout the 20th century, several other widely felt earthquakes occurred in 1928,

1956, 1970, 1979, and 2004 with magnitudes in the range of M 5.0-5.5, fortunately causing

little or no damage in neighboring regions. On a statistical basis, we expect one earthquake

with a magnitude of 4.5, 5.0 and 6.0 to occur every year, 10 years and 80 years,

respectively. The catastrophic magnitude 7 and above events might occur every several

thousands of years. A similar event to the 1927 earthquake which was magnitude 6.2

would be very harmful and destructive today considering that the total population on both

sides of the Dead Sea Fault has increased by a factor of 20 since that earthquake. Various

seismic scenarios have been explored to better understand the consequences of future

earthquakes in terms of casualties, injuries and damage as a result of moderate to strong

earthquakes along the Dead Sea fault or the Carmel fault (e.g., Levi et al., 2010).

Instrumental seismic monitoring in the Middle East started at the end of the 19th century

with the installation of station Helwan (HLW) in Cairo, Egypt. From 1898 until 1912

Helwan was the only seismological station that operated in the region, the closest stations

being more remote and including stations at Athens and Istanbul. Another important

station that started operating in 1912 was Ksara, which is located in central-east part of

Lebanon. Station JER of the WWSSN, located in the Hebrew University of Jerusalem,

started operating in 1954, and was later upgraded in 1963. During the middle of the 20th

century temporary stations operated for a short period of time in various parts of Israel

8

enriching somewhat the seismological catalog. Two seismic networks, with up to 35 short

period stations in each network, were installed in 1983, one in Jordan (JSO, Jordan

Seismological Observatory) and the other in Israel (ISN, Israel Seismic Network). With

time these networks have been upgraded and several broadband stations and

accelerometers have been installed. Since that time the seismicity of the Dead Sea fault is

continuously monitored by the ISN and JSO. In 2000 the catalogs of both networks were

merged to create a common Dead Sea Fault catalog, which is shown in Fig. 2. In addition to

these permanent networks, several temporary networks were deployed along the Dead

Sea fault, typically for 1-2 years, which further increases the database.

9

Figure 2. Seismic network (blue squares), active faults (blue lines), and seismicity (purple, red and

green dots) in Israel and adjacent regions from 1900 to 2011. Data from the Geophysical Institute of

Israel. The Dead Sea fault on the east poses the main seismic threat.

10

Given the seismic hazard in the region of the Dead Sea and Carmel Faults it is critical that

the surrounding populations remain vigilant to the risk of earthquakes. There are

multiple approaches available to mitigate the impact of inevitable future events. This

committee, and this report, focus on just one approach, that of earthquake early warning.

Guiding principles for the development of a warning system

The committee focused on designing an infrastructure for earthquake early warning that

can provide a flexible and durable state-of-the-art system within 2 years and beyond. This

basic philosophy has implications on the recommendations for both the seismic network

to be constructed, and the early warning algorithms that should be implemented.

In order to provide confidence in the warning system, early warning algorithms must be

rigorously testable and transparent. As such the alert algorithm must be openly available

to the scientific community. Such transparency ensures adjustments to the algorithm/alert

criteria that can be made as experience is gained.

The committee believes that although the expected source of large earthquakes are the

Dead Sea and Carmel faults, it cannot be discounted that seismic events producing

damaging ground motion will not occur away from these primary fault structures. From

the outset the system should be designed to issue alerts nationwide, from seismicity

occurring nationwide.

In the long term, we recommend that multiple warning algorithms should be considered.

This should include P-wave (providing information on both the location and magnitude)

and strong-shaking threshold based algorithms. The initial EEW system should use a

network-based approach, but having the option of introducing an onsite-type approach in

the future is an advantage (these various approaches are described in detail below). Also

in the long term, the alert information available should include the intensity of shaking

expected at a users’ location.

The EEW system should generate an informational alert for events smaller than are

expected to do damage. This is to exercise the system and provide informational alerts to

users. Without this ability to detect and generate informational alerts for smaller, more

11

frequent events, it will be difficult to ensure the continued functionality of the system or

the ability of the population to respond to the alerts.

In order to meet these criteria, the seismic network monitoring infrastructure requires

major upgrade and densification. The existing high gain stations require upgrade in order

to be Early Warning capable, in particular because of their low bandwidth radio and high

latency satellite communication, and because not all are sufficiently broadband. The

accelerometer network also requires major overhaul, with instrumentation to be changed

and communication to be have real-time-capability. The committee believes there should

be a single high quality Israeli seismic network, combining both weak and strong motion

sensors, which can be used for both earthquake early warning and for other forms of

seismic hazard research. This will reduce seismic hazard in addition to providing a

warning capability. All new instrumentation and communication strategies should be

optimized for earthquake early warning applications. In addition to new network sites it is

critical that the existing ISN be upgraded to similar quality sites (including hardware and

communications).

Finally, the committee recommends that alerts should not be issued until the performance

of the system (in terms of false and missed alerts) reaches a performance standard to be

defined during the evaluation and aligned with performance standards defined by other

national public warning systems.

Approaches to early warning

The concept of earthquake early warning systems (EEWS) today is becoming more and

more prevalent as a mechanism to further reduce seismic hazard. EEWSs are real-time,

modern information systems that are able to provide rapid notification of the potential

damaging effects of an impending ground shaking, through rapid telemetry and processing

of data from dense instrument arrays deployed in the source region of the event, or

surrounding the target infrastructure such as a city.

There are two primary types of EEWS. A “regional” (or network-based) EEWS is based on

a dense sensor network covering a portion of, or the entirety of an area that is threatened

by earthquakes. Relevant source parameters, e.g. event location and magnitude, are

estimated from the early portion of recorded signals (initial P-waves) and are used to

12

predict, with uncertainties, the ground motion intensity expected at a distant site where a

target structure of interest is located. Alternatively, a “site-specific” (or on-site) EEWS

consists of a single sensor or an array of sensors deployed at (or in the proximity of) the

target structure that is to be alerted, and whose measurements of amplitude and

predominant period of the initial P-wave motion are used to predict the ensuing peak

ground motion (mainly related to the arrival of S and surface waves) at the same site.

In the two cases, we expect differences in the lead-time, i.e. the time available for warning

before the arrival of strong ground shaking at the target sites. The maximum theoretical

lead-time for regional EEWS is often defined as the time difference between the S arrival at

the target and the first P arrival at the seismic network. However, an EEW system typically

requires a few seconds to detect the event, evaluate its severity, and decide whether to

issue the alert, so that the effective lead-time is always smaller. It is clear that, for such

systems, the lead-time increases with the distance of the target and with the rapidity of the

detection. If the target site is close to the epicentral area, the regional approach may not be

viable, since the lead-time may be zero, or can be too small for any application. For

regional EEWS the extent of the “blind zone”, e.g. the area within which destructive S-

waves may arrive before a warning can be issued, depends on the earthquake depth,

network coverage of the source, and the speed of the telemetry and processing system. Its

radius is typically 30km for shallow crustal earthquakes and a relatively dense network

(station spacing 20-30 km).

The onsite warning method uses the early part of the P-wave signal to predict the ensuing

peak ground motion (mainly S and surface waves) at the same site. In this case, the

theoretical lead-time can be defined as the time interval between the P and the S arrival at

the target, though, again, some seconds for detection and computation must be taken into

account. Similar to the case for the regional approach, the lead-time for the onsite

methodology increases with the epicentral distance due to the growing travel-time

difference between the slower S-phase and the faster P-phase. It is theoretically possible

that the onsite EEWS can provide a useful lead-time where a regional EEW system cannot,

due to a significantly smaller blind zone. However, the cost is the higher false alarm rates.

Still, when a regional strategy is possible, it generally provides a larger lead-time [Satriano

et al., 2010].

Earthquake Early Warning Systems have experienced a sudden improvement and a wide

diffusion in many active seismic regions of the world in the last three decades [e.g. Allen et

13

al., 2009]. They are operating in Japan, Taiwan, Mexico and California. Many other systems

are under development and testing in other regions of the world such as Italy, Turkey,

Romania, and China. Most of these existing EEWS essentially operate in the two different

configurations described above, i.e. “regional” and “on-site”, depending on the source-to-

site distance and on the geometry of the considered network with respect to the source

area. A variant to these approaches is the “front detection” EEWS, such as the Seismic Alert

System for Mexico City, which can be particularly advantageous when the only potential

seismic sources are at some distance from a populated area. The seismic warning is issued

when several nodes of a “barrier-type” network of accelerometers deployed along the

Mexican coast, trigger on earthquakes occurring along the adjacent subduction zone,

providing about 60 sec warning to the city [Espinosa-Aranda et al., 2011].

Regional EEWS

The regional EEWS approach is based on the initial P-wave signal detection at a minimum

number of near-source stations (typically 4 to 6). The automatic picks of first P-arrivals at

few stations near the earthquake epicenter are used to determine a preliminary event

location, which is further refined upon the addition of readings from more distant

receivers. Several methodologies have been proposed for the real-time, evolutionary

estimation of the earthquake location which are now implemented in the EW algorithms

(ElarmS, Virtual Seismologist (Cua et al, 2009), PRESTo) running in California, Switzerland

and Italy. The real-time magnitude estimation is generally inferred from the measurement

of peak displacement and/or the predominant period measured in the first few seconds

(typically 3-4 sec) of the recorded P-signal. In some cases, especially for stations located

very close to the source, S-wave signals can also be usefully analyzed to get rapid

magnitude estimations along with P-wave signals. Several studies based on the off-line

analysis of near-source earthquake records from different seismic areas worldwide, have

indeed shown that magnitude correlates with distance-corrected, P-wave peak

displacement and predominant period over a relatively large magnitude range. Although

the saturation of the P-wave parameters has been observed for M > 6.5-7 earthquakes,

several methodologies making use of longer time windows of the P wave and/or the S

wave to update magnitude estimates have been shown to be efficient in minimizing the

problem (Colombelli et al., 2012). The source location and magnitude estimations, which

are continuously updated by adding new station data, as the P-wave front propagates

14

through the regional EW network, are then used to predict the severity of ground shaking

at sites far from the source, through regional-specific, ground motion prediction equations.

Onsite EWWS

A different approach, the onsite techniques are generally aimed at estimating the expected

peak ground shaking, associated with S and surface waves, directly from the recorded

early P-wave signal. This is again accomplished through the use of empirical regressions

between measurements performed in the first few seconds of the P-wave signal and the

final peak ground motion. Nevertheless, there are certain onsite approaches (e.g.

Nakamura, 1988) that evaluate location (or hypocentral distance) and magnitude. They

are sometimes used as support for regional EEW systems, in order to reduce lead-times

and extend the region of applicability.

Wu and Kanamori (2005) showed that the maximum amplitude of a high-pass filtered

vertical displacement, measured on the initial 3 sec of the P-wave (namely Pd), can be used

to estimate the peak ground velocity, PGV at the same site, through a log-linear

relationship. This relationship does not depend on magnitude, in the sense that the same

values of Pd (and thus of PGV) could be due to a moderate but close earthquake or to a

large, distant event. Although initially observed for near-source records (distances < 30

km), further analyses on independent data-sets have confirmed that log PGV vs log Pd

scaling is still valid at relatively large distances, up to 300 km (Zollo et al., 2010, Colombelli

et al., 2012). Similar scaling relations have been observed between the initial P-wave

displacement/velocity/acceleration and final PGV or PGA, and implemented for onsite,

stand-alone warning systems, but the data scattering and uncertainty on peak motion

prediction generally increases passing from low- to high-frequency measurements of

ground motion quantities.

Most of the onsite EEWS currently operating are threshold-based, alert methodologies: the

alert is issued as the measured initial P-wave peak displacement/velocity/acceleration

overcomes a given amplitude threshold which is arbitrary set according to the predicted

peak ground motion value using the empirical scaling relations between P and S

amplitudes. Given that small magnitude earthquakes may have very large amplitudes but

high frequency spikes, such a basic threshold system can produce frequent false alarms. A

more robust approach is to combine the P-wave peak (which scales with distance and

15

magnitude) and P-wave predominant period (which scales with the magnitude), into a

single indicator to be used for onsite warning (Wu and Kanamori, 2005). Based on this

idea, Zollo et al. (2010) and Colombelli et al. (2012) have proposed a threshold-based EW

method based on the real-time measurement of the period (τc) and peak displacement

(Pd) parameters at stations located at increasing distances from the earthquake epicenter.

The recorded values of early warning parameters are compared to threshold values, which

are set for a minimum magnitude 6 and instrumental intensity VII, according to the

empirical regression analyses of strong motion data from Japan, Taiwan and Italy. At each

recording site the alert level is assigned based on a decisional table with four alert levels

defined upon critical values of the parameters Pd and τc,. Given a real time, evolutionary

estimation of earthquake location from first P arrivals, the method furnishes an estimation

of the extent of potential damage zone as inferred from continuously updated averages of

the period parameter and from mapping of the alert levels determined at the near-source

accelerometer stations.

P-wave based, regional and onsite EW methods can be integrated in a unique alert system,

which can be used in the very first seconds after a moderate-to-large earthquake to

determine the earthquake location and magnitude and to map the most probable damaged

zones, using data from receivers located at increasing distances from the source.

Front detection or barrier EEWS (S-wave threshold EWS)

This is essentially a modified variant of the onsite approach, where a barrier-shaped,

accelerometric network is deployed between the ‘a priori’ identified source region and the

target site/region/infrastructure to be protected. The alert is issued when two or more

nodes of the seismic fence record ground acceleration amplitude larger than a default

threshold value. For typical regional distances, the peak acceleration at the barrier nodes

is expected to be associated with the S-wave train, so that the distance between the

network and the target is set to maximize the lead time, which is, in this case, the travel

time of S waves from the barrier to the target site. The most important examples of front

detection EW systems are the barrier-type, Seismic Alert System (SAS) for Mexico City and

the ring-type EW system for the Ignalina Nuclear Power Plant (INPP) in Lithuania.

There are few recent and contradictory reports about the performance of the Mexican

system. In a recent study, Iglesias et al, (2007) pointed out that SAS’s performance during

16

1991–2004 revealed a surprisingly high rate of failure and false alerts. The authors

attribute this poor performance to an inadequate detection algorithm and a limited areal

coverage by the SAS. Nevertheless, the SAS, implemented in 1991, is the first public

warning system and continues to provide ~60 s warning to Mexico City.

The proposed Early Warning system for Israel

Based on the specific geographic distribution of the major earthquake causative fault

systems (Dead Sea and Carmel Fault Zones) two complementary, basic approaches for an

Early Warning System are feasible for the whole territory of Israel.

The first follows the “front detection”, early warning concept, by using the data from a

dense, nearly linear array of accelerometric sensors deployed parallel to the Dead Sea and

Carmel fault zones. S-waves radiated by moderate to large earthquakes (M > 5) occurring

along these fault zones, would trigger the closest nodes of the accelerometric network and

an alert is issued as the recorded peak acceleration passes a predefined threshold.

According to preliminary computations presented in a report entitled: “Assumptions and

guidelines for building an earthquake early warning system in Israel” by V. Pinsky

(Geophysical Institute of Israel), given an average station spacing of 5 kilometers and

requiring that the pre-determined acceleration threshold be exceeded at two adjacent

stations, results in warning times of about 10-14 seconds at an epicentral distance of

about 60 km, for events located up to 15 km from the array and whose epicenter is up to

25 km deep. Based on earthquake distribution analysis and extrapolation of ground

motion empirical relations (Boore et al., 1997), an average false alarm rate of 3 per year

has been inferred for a detection threshold of 70 gal and station spacing of 5 kilometers.

This value has to be finely calibrated in order to minimize the false alarms, which is the

severe weakness of this type of early warning approach. Inspection of the national

accelerometer network data set reveals that this threshold has been reached twice during

the past 2 decades: in Elat, 90 km from the Mw=7.2 Aqaba bay earthquake of 1995 and in

Yitav, 30 km from the Mw=5.1 Dead Sea earthquake of 2004. The latter may be considered

as a "false alarm".

Such a front detection, S-wave threshold-based early warning system has some

advantages: (a) it can be built with (relatively) cheap sensor technology using Micro

17

Electro-Mechanical System (MEMS) accelerometers, (b) it by-passes the need to estimate

earthquake location and magnitude, which require the detection of the P-wave arrival and

sophisticated algorithms running in real-time. (c) As it provides only an approximation of

the earthquake severity based on the recorded ground motion, simple algorithms are

needed.

Nevertheless, several disadvantages should be carefully considered, if this option is

uniquely selected for an early warning system for Israel: (a) Since the system does not

provide information about the location and magnitude of the potential damaging

earthquake, when ground shaking above the threshold is observed over a wide section of

the seismic fence array, the only option would be to alert the entire nation. Similar to

current strategies for missile early warning, knowing the original position of the

earthquake source and its magnitude could greatly help into identify and select the areas

where the potential damage is expected to be more severe and therefore to be alerted with

a high priority. (b) If the earthquake occurs far from the seismic fence, within the Israel

territory, the S-wave threshold system would likely fail, since the recorded acceleration

may be below the threshold, depending on the distance from the array and on the event

magnitude. (c) Such a threshold-based approach would likely be set to activate only for

large events/amplitude triggers in order to reduce the number of false alarms due to low

magnitude events, occurring in proximity of the accelerometer array or due to moderate

earthquakes at regional distances. Selecting the appropriate threshold can be very difficult

to optimize. Also, given that the system should only trigger for big events, it cannot be

exercised and tested other than in major earthquakes.

A complementary early warning approach is the (integrated regional/onsite) P-wave

based method, which uses the initial P-wave information recorded by near-source, dense

accelerometer arrays deployed in the proximity of the active faults. P-waves travel about

twice as fast as S-waves, but have smaller amplitudes, thus making possible a more

complex, but still feasible real-time detection and analysis. Indeed a rich library of

algorithms and software packages are available for the automatic picking and association

of first P-wave arrivals from sparse digital networks. The use of accelerometers prevents

amplitude saturation and clipping, which are very likely at near-source distances of a

moderate to large earthquake (M>4). Moreover, the recent experience of real-time seismic

monitoring in Italy and Switzerland, using co-located velocity and accelerometer sensors,

confirms that high quality acceleration sensors can provide high quality P-wave

18

recordings of small to large size earthquakes (M>2) at local distances (< 50 km), when

combined with wide dynamic range data-loggers (e.g. 24 bits).

The P-wave based, early warning approach has the main advantage to allow the

determination of the earthquake location and magnitude, which are used to predict the

peak ground motion at any distant locations through existing ground motion prediction

equations (GMPE). At the same time, onsite estimations of final peak ground motion can

also be inferred from the initial P-wave ground motion amplitude. When combined with

contemporary measurements of the P-wave characteristic period, the extent of the

potential damage zone can be rapidly assessed by using P-wave data from stations located

at increasing distances from the source (e.g., Colombelli et al., 2012).

We stress that, assuming continuous data-streaming from the near-source accelerometer

array, the information carried by P-waves does not replace information from PGA (or PGV)

associated with S-wave phases, but can complement it and can be used to

confirm/validate/cancel an issued alert at sites distant from the source.

Other important advantages of the P-wave based approach are that: (a) it allows detection

of events for a wide magnitude range, permitting regular testing and continual

optimization of algorithms using the frequently occurring earthquakes below alerting

thresholds, (b) it can provide location specific alert information (the so-called “dynamic

grid” for warning), (c) it would provide fewer false and missed alarms than an S-wave

based threshold system, and (d) the system is potentially able to provide warning for

earthquakes occurring throughout and outside the territory of Israel.

There are also drawbacks to the P-wave based approach: (a) It requires higher quality

seismic stations (more expensive than for the S-wave based threshold system), including

high sensitivity acceleration sensors and wide dynamic range data-loggers, with enhanced

capability of data processing, storage and transmission, (b) Such an approach needs to

operate a sophisticated system running real-time algorithms for detecting P-waves,

associating arrival from different stations to declare an event, providing an evolutionary

estimation of location and magnitude along with uncertainties, and predicting the peak

ground motion at the site and elsewhere by using local measurements and/or attenuation

relationships.

19

The challenges of greater complexity are balanced against the benefits of more complete

real-time earthquake information. It is for this reason that the P-wave based EEWS are the

most commonly used approach to early warning around the world. This also means that

there is a large supporting, open source and active community, which facilitates efficient

exchange of know-how and software.

Our proposal for an Israeli early warning system is to design and build a real-time, seismic

network, equipped with acceleration and velocity sensors, which operates integrated P-

wave based and S-wave based threshold methodologies. This can be realized through:

• The deployment of a dense array of accelerometers as close to the Dead Sea and

Carmel fault as possible, arranged as a staggered geometry (including pre-existing

ISN stations), with two parallel lines of sensors north of the Dead Sea and one line of

sensors south of the Dead Sea. The accelerometer array can be supplemented with

about ten seismometers co-located with the accelerometers and distributed along

the faults to improve the detection and analysis of background fault microseismicity.

After the system has been evaluated and proved operational, an additional ten

stations with co-located seismometers and accelerometers should be deployed

across Israel to create an even distribution when combined with the existing seismic

network (ISN) with the aim to (1) provide early warning for events that do not occur

on the main faults, (2) calibrate the P-wave based parameters for EEW, and (3)

develop intensity attenuation relationships that will be used to provide alerts that

include the predicted intensity. This deployment is shown in Fig. 8.

• The installation of uniformly high quality broadband and wide dynamic range

accelerometer and seismometer sensors that will allow for a full range of early

warning applications, i.e. both S-wave based threshold and also P-wave based

approaches.

• The implementation of a fast, robust and secure data transmission system

minimizing the data acquisition and transmission latency.

• The implementation of a (centralized) real-time, automatic, data processing and

management software platform (i.e. SeisComp3 or Earthworm) for the detection and

analysis of current microseismicity and continuous data streaming analyses running

P-wave based and S-wave based threshold algorithms.

20

Simulated early warning performance in Israel

Assessment of alert times

Here we assess the alert times for several approaches to early warning for several

network geometries in Israel. Note we only consider the delay due to the geometry of the

network and the type of waves being measured. In an operational early warning system,

there are other significant delays independent of these factors, including delays due to

data transmission, data processing, and alert dissemination. We consider 3 approaches:

(1) An S-wave based threshold method triggered by the S-wave arrival at the second

station, i.e. large amplitude shaking must be observed at 2 stations for the alert to be

generated.

(2) A P-wave method triggered by the P-wave arrival at the 4th station, i.e. required 4

station P-wave arrivals to alert. This is the number of stations required by several

early warning algorithms currently under testing around the world.

(3) A P-wave method triggered by the 6th P-wave arrival. This is also included as the

ability to generate alerts based on 6 P-wave triggers and will soon be available within

SeisComp3.

Two network geometries are considered in this analysis:

Network geometry A: The existing ISN network assuming all stations have been

upgraded and are early warning ready. The alerts times for the 3 EEW approaches are

shown in Fig. 3.

Network geometry B: A staggered array along the northern Dead Sea and Carmel faults

with spacing of 10 km in each line, a single array along the southern section of the fault

with 10 km spacing, and the upgraded existing ISN network (Fig. 8a). The alert times are

shown in Fig. 4. This is the minimal network geometry required for IEEWS (termed

"sparse" in the simulation figures) and the one proposed in this report.

Network geometry C: The final network geometry required for IEEWS (termed "dense" in

the simulation figures) includes a staggered array with ~10km spacing in each line along

the entire Dead Sea and Carmel faults, and the upgraded existing ISN network plus 10

additional stations across Israel (Fig. 8b). The comparison of this network performance

with the minimal network geometry (Network geometry B, Fig. 8a) is shown in Fig. 5.

In Figures 3 and 4, the sub-panels A, B and C show the delay in seconds (given by the

color) for the seismic waves (P-wave for A, B; S-wave for C) to arrive at the indicated

21

number of stations for an earthquake occurring at a depth of 10 km below that point in the

region of Israel. In subpanels D and E, for an earthquake occurring at that point, the color

indicates the difference in time for the S-waves to arrive at 2 stations and the P-wave to

arrive at 6 stations (D) and 4 stations (E). Hence (D) shows the difference in warning time

between the S-wave threshold solution and the robust P-wave solution using 6 picks; and

(E) shows the same threshold solution against a P-wave solution using 4 picks. In (D) and

(E), warm colors indicate regions where the P wave approach is faster than the S-wave,

and cold colors indicates places where the network geometry means the S-wave approach

will be faster than the P-wave. It should be noted that the delay times for the S-wave

approach are minimum estimates, as the ground acceleration is likely to exceed the pre-

determined threshold value some time after the arrival of the S-wave.

It is important to note that across most of Israel, and in particular the Dead Sea and Carmel

faults, the difference in arrival times between the S-wave threshold and P-wave at either 4

or 6 stations is under 2 seconds. This delay is comparable to delays that can be introduced

by data-logger packet size, communication, and processing. Note that the difference in

performance is near zero across the entire network for the preferred dense network

option, and in some areas along the Dead Sea and Carmel Faults, the P-wave algorithm

provides faster warning.

In A, B and C, it is clear that for the dense option the absolute delays are typically under 4s

across Israel for each method, and on the order of 2 seconds around the Dead Sea and

Carmel fault regions as well as the area near Lebanon. This is significantly better than

using the existing network of Israel alone.

Figure 5 shows the difference in alert times between the different network geometries.

The major improvements in alert times are focused along the 2 fault lines. With the

"dense" network geometry, alert times are lower across the nation.

We assume that all stations are operational all the time, earthquake depth is 10km, and P

and S-wave velocities are fixed (6 and 3.5km/s respectively). There is no consideration

given to delay in data transmission, or processing delay for an S-wave threshold or P-wave

EEW algorithm, and there is no discussion of the sensitivity of each method to various

magnitude sizes.

22

Figure 3. Alert time analysis for the existing ISN network upgraded to early warning capable

stations (network geometry A). Panels A-C: the color of each point on the maps illustrates the time

at which an alert would first be possible for an earthquake at that point according to the various

early warning approaches. For every location on the map, the color scale indicates the time

required for a P-wave to reach 4 stations (A), 6 stations (B), or an S-wave to reach 2 stations (C).

Panels D, E: the difference between the alert time for the various methods at any given location is

indicated by the color scale.

23

Figure 4. Alert time analysis for a ~10 km spaced array along the Dead Sea and Carmel Faults plus

the existing ISN network upgraded to early warning capable stations (network geometry B). See

Fig. 3 caption for explanation.

24

Figure 5. The differences in arrival times between the proposed network geometry ("sparse") and

the ISN geometry ("existing") for the 4 P-wave (A), 6 P-wave (B) and 2 S-wave (C) algorithms. The

main benefit of the proposed network is seen in the dramatic reduction in travel time for events

that would occur along the Dead Sea fault. The difference between the "dense" (network geometry

C) and the "sparse" network options are shown in panels D-F. The main benefit here is seen in the

reduction of travel time across the Arava Valley and other parts of the country away from the

known faults, which reflect the improved overall network density of the dense model.

25

Simulations of P-wave approach

The performance of a typical P-wave based, early warning system for Israel is studied

using the algorithm PRESTo (Probabilistic and Evolutionary Early Warning System)

(Satriano et al., 2010) presently implemented and operated by the ISNET network in

southern Italy (http://isnet.na.infn.it/presto_index.php). PRESTo is a software platform

for regional earthquake early warning that integrates recently developed algorithms for

real-time earthquake location and magnitude estimation into a configurable and portable

package. It has been very recently upgraded to evaluate alert levels and the extent of the

Potential Damage Zone, by combining real-time, evolutionary measurements of initial P-

peak displacement and predominant period at the network station sites (Zollo et al., 2010;

Colombelli et al., 2012).

We have performed a set of off-line simulations for potential Mw 6-6.5 events occurring

along the Dead Sea Fault north of the Dead Sea, north of the Sea of Galilee, and along the

Carmel Fault (Fig. 6). Two different network geometries have been used for the analysis,

network geometries B and C as described in the previous section. Synthetic accelerograms

have been computed assuming a point source, double couple earthquake source

mechanism, while the theoretical Green’s functions are obtained by the complete wave-

field, discrete wave number method (Bouchon, 1971; Coutant, 1989) for a 1-D layered

elastic/anelastic velocity model. The source time function of earthquakes has been

assumed to have a trapezoidal shape, whose duration and amplitude was compatible with

the one expected from a constant stress-drop source scaling relationship between moment

and duration. The 5-Hz low-pass filtered, three-component acceleration time series

simulated at the different network nodes have been played-back into the PRESTo system

as if they were real-time recorded and acquired by the EW network control server.

Animations of the output for all three events and the two network geometries may be

found in the following link:

http://people.na.infn.it/~zollo/Early Warning/EW Israel 2012/Report PRESTo.

Fig. 7 shows a snapshot of an output animation for the Mw 6 earthquake on the Carmel

Fault.

26

Figure 6. Map showing the locations of the three simulated earthquakes.

27

Figure 7. The left-hand panel shows the waveform time-series at the station of the new network

with the P-wave arrivals identified in yellow and the S-wave arrivals in red. The upper-right map

shows yellow and red circles indicated the distance that the P- and S-waves have travelled at this

point in time. The stations are indicated as yellow triangles and the numbers on the stations

indicate the strong shaking threat level, 3 representing intensities with MMI > 7. The lower right

figure shows the time history of the magnitude estimate.

28

Table 1 summarizes the main results of the simulation study. We have used all stations

with latitude greater than 31.5° and two network configurations, network geometries B

and C as described above. In the three analyzed cases, the first alert is available 3-4

seconds after the first P-wave pick, and 5-6 seconds after the origin time. This time

includes the arrival and detection of P-wave at minimum 5 closest stations, and the use of

a minimum of 2sec of the P-wave signal.

Table 1. Summary of performance for the three simulated earthquakes.

First

Alert

Minimum Lead

Times

Delta

Hypo

Delta

Mw

Mw

Error

Note

Carmel Fault

(Mw 6)

3 s after

1st pick

5 s after

OT

Jerusalem : 21s

Tel-Aviv: 16s

Haifa: 3s

< 2 km -0.1 ±0.1 Stable after

10 s from

OT

Dead Sea (Mw

6.5)

3 s after

1st pick

5 s after

OT

Jerusalem : 10s

Tel-Aviv: 14s

Haifa: 18s

< 0.1 km <0.1 ±0.05 Stable after

10 s from

OT

Sea of Galilee

(Mw 6.5)

4 s after

1st pick

6 s after

OT

Jerusalem : 26s

Tel-Aviv: 23s

Haifa: 10s

< 0.5 km <0.1 ±0.1 Stable after

10 s from

OT

Due to the proximity of the event epicenters to the seismic “fence” along the faults, no

significant differences are observed in the early warning system performance using the

“sparse” (network geometry B) or “dense” (network geometry C) configurations, so only

parameters for the “sparse” case are reported in the table. We expect that significant

improvements in the system performances should be observed using the “dense” seismic

fence for events located at larger distance from the array.

29

The minimum lead time, i.e. the time between the first S-arrival at the city and first alert

time, at three main cities depends on the earthquake location. It varies between 10 and 26

sec for Jerusalem, 14 to 23 sec for Tel Aviv and 3 to 18 sec for Haifa.

The simulation shows that we should expect relatively small errors in the earthquake

location and magnitude as provided by the P-wave based EEWS, so that reliable peak

ground motion predictions could be obtained by using attenuation relationships. The

extent of the potential damage zone, as determined by the area embedding the maximum

alert level nodes (e.g. alert level 3), is well defined in the three cases, corresponding to the

zone where instrumental intensity IMM > 7 is observed, the latter being derived from the

measured Peak Ground Velocity (Wald et al., 1999) (Fig. 7).

Recommendations for software implementation

In order to effectively manage the new seismic network architecture, and provide a

platform for EEW algorithm development and testing, we strongly suggest adoption and

operation of an open source, community supported package for seismic network data

operation. There are unfortunately only a few good options available to the monitoring

community at the moment, and Earthworm and SeisComP3 are the two strongest solutions.

The committee recommends using SeisComp3 for the following reasons:

- This is an open source network solution being adopted and developed by other

groups in Europe and across the globe

- The Geophysical Institute is already running it

- There is currently development of a Virtual Seismologist magnitude determination

module for SeisComp3

- The software includes fully tested and standard modules for data acquisition,

archival, automatic event detection and quantification, manual event review,

catalogue management and alert services - all using a single database – this

constitutes a full suite of features for managing the seismic network.

The committee recommends that the GSI will develop EEW modules on top and/or within

SeisComp3:

30

- The first (simplest) module is an S-wave threshold-based approach. This could be

designed by GSI and developed through a contract to GEMPA (software

consultants for SeisComP3).

- Components of the Virtual Seismologist algorithms will be available over the

course of the next year (from ETH)

- SeisComp3 provides a solid platform for further development to be made with new

algorithms based on research into early warning algorithms in Israel for Israel

- Other early warning groups are likely willing to share code for implementation but

this will require knowledgeable local support.

Recommendations for early-warning capable network stations

For stations within a seismic network to be capable of contributing to the types of early

warning systems being proposed in this project, each needs to be of a minimum standard.

An early warning ready station needs to continuously provide high quality data at high

sample rates, with a very high uptime, and minimum latency, to the seismic network

processing hub. It also needs to operate robustly for years to decades.

We break down the minimum requirements for the following station components: 1) the

sensor; 2) the data-logger; and 3) the peripheral station infrastructure, which includes

communications, power supply, and station housing.

Sensor: The new network will consist of (a) co-located high gain velocity sensors and low

gain strong motion accelerometers, and (b) stand-alone accelerometers. The goal for each

sensor is to provide on-scale, high quality records for both small earthquakes (to test and

calibrate the system, and collect high quality earthquake data with which to create a high

quality earthquake catalogue) and large earthquakes. Each sensor should reach the

following criteria:

- flat frequency response from

o 50Hz-50s for high gain sensors

o 100Hz-DC for strong motion sensors

- dynamic range of at least 120dB for each sensor

- sensor saturation of at least 1g for the strong motion sensor

Data-logger: The data-logger should be capable of

31

- Digitizing the full dynamic range of the signals recorded by the sensors. At

minimum the digitizer should be 21-bit, preferred is 24-bit.

- Sample rates of at least 100sps.

- Providing GPS timing with time resolution reaching or exceeding 1ms.

- Providing onsite recording of at least 3 months of continuous data at high sample

rates (in case communication is lost during a critical seismic sequence)

- Recording packets either natively in seed format and provide SeedLink

communications, or provide a well known format with durable software for

acquisition and conversion to mseed / SeedLink.

- Supporting multicast of the signal, so independent seismic processing hubs can

each receive the data.

Peripheral infrastructure:

- Communications: minimal latency, not greater than 3 seconds for 99% of packets

- Communications: bandwidth exceeding at least two times the average throughput

of the data.

- Communications: minimal gaps or out-of-sequence data packets

- Power: backup power supplying at least 2 weeks of independent power (typically

battery or solar)

- Security and robustness: the vault sensors, datalogger, and communications

should be secured from vandals and easy manipulation.

It should be noted that the station is not independent of the entire seismic network. The

datalogger and communications selected should be supported by appropriate acquisition

software at the network hub that allows rapid processing of the data packets so that the

overall latency of data is at an acceptable level. The entire system should be capable of

providing 99% of data to the EEW processing software with a latency of less than 5s.

Further, the overall noise measured by the seismic stations should be low enough to

ensure that the high quality instrumentation is being effectively used, and the station is

capable of recording with high signal-to-noise ratio the maximum number of earthquakes.

We recommend, for broadband high gain stations, that between 30Hz and 20s, the typical

station noise is at least 20dB below the High Noise model of Peterson (1993). Excellent

seismic stations should significantly exceed this level, and operate near the low noise

model at long periods out to 100’s of seconds. Strong motion stations should not exceed

the High Noise model across this same frequency band. We recommend that noise tests

32

lasting at least 1 week should be made at all candidate sites, with data processing via PQLX

to help interpret results in a homogenous manner. Achieving this noise level requires

careful site selection, and proper thermal insulation of each sensor.

It is important to reiterate the importance of reliable stations with high uptime. A crucial

component for having confidence in the seismic system is, at least for the sensor and

datalogger, having sensors that have demonstrated their successful performance in similar

networks. Independent confirmation of good performance by other network operators can

provide this confidence.

Both the datalogger and sensor must provide full system response in known format

(dataless Seed)

Proposed initial design

We propose a specific two-year plan for implementation of an early warning system in

Israel. This plan is obtainable within the budget and timeline provided and will achieve

the primary objective of delivering earthquake alerts to schools across Israel. The key

components of the initial two-year plan are as follows.

Install 55 new seismic station sites and integrate their operation with the existing ISN.

The recommended network design is “Network Geometry B” as described above, and is

shown in Fig. 8a. The network should consist of:

• Fifty (50) accelerometer-only sites as close as possible to the Dead Sea and Carmel

Faults (within 15 km) creating a staggered geometry (including pre-existing other

stations) with a spacing of 10km. This will create two parallel echeloned lines 10

km apart with stations every 10 km along each line, from the Dead Sea northward.

South of the Dead Sea there will be one line of sites spaced 10 km apart. This

configuration provides the very high-density network along known faults to

maximize warning time. Some of these stations can be installed in existing

bunkers where available.

• Five additional co-located seismometers and accelerometers along the Dead Sea

and Carmel Faults so that there will be a sufficient density of this type of stations

along the known hazardous faults.

33

There are also additional components and improvements to the system that are strongly

recommended but will not fit into the two-year plan and budget. These include deploying

additional seismometers (rather than just accelerometers) and densification of stations

across all of Israel (see network geometry C below, Fig. 8b). There are several reasons that

we recommend this network expansion. First, to calibrate the P-wave based parameters

for early warning using events with as wide a range of magnitude as possible. Second,

having high sensitivity stations and instrumentation across the country will facilitate the

development of intensity attenuation relationships that will be used to provide alerts that

include the predicted intensity. Third, having a dense network of stations across the

country will provide a warning capability for earthquakes occurring on faults anywhere in

Israel including unknown faults, or faults which are currently thought to be of low hazard.

Network operation and management software that can efficiently process all the data from

the existing and new seismic stations must be installed. This should be located at the

seismology division and should use an open source, community supported software

package. This system will perform all of the network operations that seismic networks

around the world operate including earthquake detection, location, magnitude

determination, catalog generation, data archival, data access etc. In addition, it will

provide earthquake alerts. Once the network hub at the seismology division is operating

satisfactorily, a second identical redundant hub at a separate geographical location should

be set up.

34

Figure 8a. Map of the recommended initial deployment plan (minimal requirement – configuration

B). The new stations are shown as blue triangles for the seismometer plus accelerometer stations

and red circles for the new accelerometer stations. The existing ISN sites are shows as green

triangles for seismometer sites and yellow circles for accelerometer sites.

35

Figure 8b. Map of the recommended final deployment plan (optimal requirement – configuration

C). The new stations are shown as blue triangles for the seismometer plus accelerometer stations

and red circles for the new accelerometer stations. The existing ISN sites are shows as green

triangles for seismometer sites and yellow circles for accelerometer sites.

36

The development, testing, and implementation of at least one early warning algorithm

should be undertaken. We recommend an initial implementation of an S-wave based

threshold system as this is the simplest possible approach and as such is the only one that

can be implemented within 2 years. It is important that development continues in order to

implement the preferred P-wave based approaches. An initial P-wave based approach

based on modules available for SeisComp3 will also likely be available within this two-

year timeframe.

Finally, we recommend upgrading all existing ISN sites to the same standards as the new

sites. This includes hardware at the sites, communication and integration of the data

streams with data from the new stations. The committee understands that this upgrade

will be financed from a separate budget. Completing this upgrade is critical.

Timeline and budget for implementation

Timeline

A preliminary timeline charting the development over the 2 years project duration for the

EEW system in Israel is presented in Fig. 9. We divide the project into two equally

important independent and parallel components: (a) the installation of the seismic

network and (b) the design and implementation of applications for seismic data

processing at the hubs.

(a) Installation of the Seismic network: The installation of the seismic network should

include two concurrent preliminary stages: (1) Procurement of seismic equipment

(including creating detailed requirements for equipment, requesting bids from

manufacturers, evaluating bids and testing candidate sensors, making final orders and

receiving the first equipment batches). This should last at least 6 months but not more

than 9 months. (2) Vault design and site selection including testing of background noise

levels and gaining permissions. The majority of sites should be selected within the first

year, but this stage can remain active for the duration of the project.

After the procurement stage is completed, the installation of accelerometers and

seismometers can begin. The proposed timeline assumes installation of about 4

37

accelerometer sites and 1 seismometer site per month. This is a very ambitious timeline,

but can be achieved with sufficient dedicated staff and solid planning.

(b) Creating the seismic data processing hubs: Prior to the design and installation of

EEW software applications at the hubs the preferred earthquake management software

should be configured (this software is likely SeisComP3). This will require a major effort at

the initial stage, and will also be an ongoing effort, with optimization continuing

throughout the life of the software. Once a high level of competence in SeisComP3 is

attained, investigation into the development and testing of the EEW algorithms should

begin. The preferred plan for the early warning system is to focus on building an S-wave

based threshold system immediately. The major first step is to develop the full

requirements for this as a SeisComP3 module and contract and work with the community

programmers to implement this module. Once installed, a period of testing is required to

observe the system, optimize the parameters and to minimize false alarms. After the

system is stable, the GSI should begin to introduce the software to the authorities

responsible for alerting and then begin sending alerts to downstream users.

At the same time as developments in the S-wave based threshold method are underway,

the early warning operations team should also become familiar with the on-going

community developments to include P-wave early warning algorithms into SeisComP3.

They should install existing modules, and understand how warning times can best be

reduced, locations and magnitudes be made more reliable, and alerts are best

disseminated to the user community.

As an earthquake service providing early warning, it is required to be robust, always

available and always operational. A careful investigation into the IT requirements for a

very high availability network hub, including possible redundancies, is required. Once a

plan for the hardware configuration to meet the security and high availability

requirements is developed, it should be installed at the first hub. Once the concept has

proven to be successful, an installation will follow at the second, geographically redundant

but identical processing hub. Monitoring software that continuously checks for problems

in hardware, software or communications should be installed.

38

Figure 9. Timeline for the development and implementation of an early warning system in Israel.

39

Estimated budget

The budget (Table 2) is based on the recommended system (configuration B).

Table 2. Budget outline for the construction of the new seismic stations

Item Number Price per

unit (NIS)

Total (NIS)

Site survey

Site selection and configuration

300,000

Site response testing

830,000

Sub-total site

survey 1,130,000

Site construction

Hardware

AB 38 95,000 3,610,000 AV 12 155,000 1,860,000 ASV 5 215,000 1,075,000 Personnel 4 800,000 3,200,000 Field expenses 2,000,000

Sub-total site

construction 11,745,000

Hubs

Hardware, security, monitoring, construction

1 2,900,000 2,900,000

Software 600,000 Personnel 5 800,000 4,000,000

Sub-total hubs 7,500,000

Estimated Total 20,375,000

40

The budget for site constructions will include:

(a) 38 accelerometers in existing IDF / Kibbutz bunkers, shelters or building basements

(AB), 12 accelerometers in new vaults (AV) and 5 combined accelerometers and

seismometers in new vaults (ASV).

(b) Personnel and field expenses

Hub construction will include:

(a) Hardware, security, monitoring, software contracts, and construction expenses.

(b) Personnel dedicated to the development and operation of the system.

Additional budget from separate sources should be allocated to the upgrade of the ISN

sites to standards similar to the new sites.

Important improvements beyond the initial 2-year plan

The strategy that the committee recommends for the initial 2-year development of the

early warning system in Israel is to create an advanced, real-time seismic monitoring

infrastructure, equipped with high quality velocity and acceleration sensors, deployed

along the most hazardous faults, i.e. the Dead Sea and the Carmel fault systems, and inside

the national territory. During this initial phase the committee recommends to install the

minimal number of stations (configuration B above, Fig. 8a) that will (1) provide the

requested early warning, (2) meet the approved budget. Regarding the early warning

approach, during this initial phase the priority is to implement the S-wave based threshold

algorithm, which should be a module in the software platform for the real-time data

acquisition, processing and storage. Having an initial P-wave based approach using

SeisComp3 modules that are currently under development should also be possible.

The committee highly recommends that scientific developments continue in the 2+ years

following the initial early warning system installation. Research should be focused on

improving the P-wave based regional methodologies available and installed for Israel.

Given the real-time, continuous data streaming from the early warning network, the

methods should be able to automatically detect and pick first P-arrivals from near-source

receivers, to declare an event, to estimate its location and magnitude along with

uncertainties, to predict the maximum ground shaking amplitudes at the target sites to be

protected and to broadcast the alerting message to end-users and decision makers. Several

41

different approaches are actually available from the research groups in USA, Italy,

Switzerland, Taiwan and Japan. A selection of these methods could be implemented and

run in parallel during a testing period of ~1 year. System thresholds should be set in order

that the early warning system can operate for small magnitude events (M>2.5), which will

ensure a sufficient number of events for calibrating and testing the different

methodologies.

The data analysis and performance evaluation during the testing period will allow

determination of whether to maintain/extend the existing early warning algorithms or to

develop new ones, specifically designed for the seismic hazard in Israel and incorporated

into the reality of the network geometry. After this evaluation period, the committee also

recommends to build a second backup hub, and to reexamine whether there is a need to

densify the network to its optimal, preferred shape (configuration C above, Fig. 8b).

A further possible development will concern the implementation of an “onsite” approach

that may provide alerts inside the blind zone of regional network warning system. This

can be initially tested using stations of the regional/ISN network that are close to schools.

If “onsite” warning proves valuable, additional stations would be needed at other schools,

which are the primary target buildings to be protected by the Israel EW system.

The continuous evaluation of system alert performance based on recordings of small to

moderate earthquakes will allow (a) identification of areas for prioritized improvement,

and (b) evaluation of the overall system robustness for redundancy and security and

consideration for dual communication paths, e.g. DSL and cellular.

Other real-time earthquake information products can also be developed as by-products of

the monitoring infrastructure. These may include methods for the fast mapping of the

strong ground shaking soon after an earthquake (e.g. ShakeMaps), estimating the location

and size of the potential damage zones, or to rapidly locate earthquakes which occur

outside the Israel territory, by using array analysis techniques.

In the line with recent advances in USA and Japan, further development should consider

the incorporation of real-time GPS into the early warning system. This will require both

the addition of real-time GPS stations and also the development of algorithms to make use

of the GPS data for early warning.

42

Finally, consideration should be given to the possibility of increasing the number of users

beyond schools, with the final destination of applying the system nationwide. Gathering

feedback from a range of users could be of great benefit for the improvement and durable

performance of the early warning system.

Building seismological capacity in Israel

Because it is located on the edge of the seismically active Dead Sea Transform, which is

known to have caused extensive damage and life losses over the past millennia, Israel

should excel in the field of earthquake science (as it does in several other prestigious

scientific disciplines). The planned upgrade and extensive expansion of the existing Israeli

seismic network should be viewed as a step towards fulfilling this vision.

We were happy to learn that the Israeli government has decided to build an earthquake

early warning system, but at the same time we wish to "alert" the decision makers that the

building and the long-term maintenance of such a system is a major seismological

undertaking that requires dedicated and extremely well trained personnel. Indeed, other

nations, that have implemented or are close to implement an effective earthquake early

warning system, are able to do so thanks to their excellent governmental and/or academic

earthquake research centers. Earthquake early warning is currently an area of intense

research, and it is vital that Israeli seismologists will become a dominant part of this

research group and be aware of new developments. In order to support the development

and the successful operation of the early warning system, a generation of Israeli

seismologists must be educated, supported and trained. This must start with the

encouragement of students in seismology, and continue with the development of fulfilling

career paths for them in Israel.

We strongly recommend that the Israeli government will encourage and financially

support exchange of students, post-docs and experienced researchers from and to Israel

for earthquake research including early warning. After the new seismic network is

installed, high quality seismic data will become available. These data should be effectively

mined to improve understanding of seismic hazard and seismotectonics, including ground

motion attenuation relations, site effects, fault mapping and delineation using

microseismicity and probabilistic seismic hazard assessment.

43

Bibliography

Allen, R. M., P. Gasparini, O. Kamigaichi, and M. Böse (2009). The Status of Earthquake

Early Warning around the World: An Introductory Overview, Seismo. Res. Lett., 80(5), 682-693 doi: 610.1785/gssrl.1780.1785.1682.

Bouchon, M. (1981). A simple method to calculate Green's functions for elastic layered

media Bull. Seism. Soc. Am., 71:959-971 Boore, D. M., W. B. Joyner, and T. E. Fumal (1997). Equations for estimating horizontal

response spectra and peak acceleration from western North American earthquakes: A summary of recent work, Seismol. Res. Lett. 68, 128–153.

Colombelli, S., O. Amoroso, A. Zollo, and H. Kanamori (2012). Test of a Threshold-Based

Earthquake Early-Warning Method Using Japanese Data. Bull. Seism. Soc. Am., 102(3), p. 1266–1275.

Coutant, O. (1990). Programme de Simulation numerique AXITRA, Rapport LGIT,

Universite´ Joseph Fourier, Grenoble, France. Cua, G., M. Fischer, T. Heaton, S. Wiemer (2009). Real-Time Performance of the Virtual

Seismologist Earthquake Early Warning Algorithm in Southern California, Seism. Res.

Lett. 80(5), 740-747 doi:10.1785/gssrl.80.5.740 Espinosa-Aranda, J. M., A. CuÈllar, F. H. RodrÌguez, B. Frontana, G. Ibarrola, R. Islas, and A.

GarcÌa (2011). The seismic alert system of Mexico (SASMEX): Progress and its current applications, Soil Dynamics and Earthquake Engineering, 31(2), 154-162.

Iglesias, A. , S. K. Singh, M. Ordaz, M. A. Santoyo, and J. F. Pacheco (2007). The seismic alert

system for Mexico City; an evaluation of its performance and a strategy for its improvement

Bull. Seism. Soc. Am., 97(5):1718-1729 Levi, T., B. Tavron, O. Katz, R. Amit, D. Segal, Y. Hamiel, Y. Bar-Lavi, S. Romach, A. Salamon

(2010). Earthquake loss estimation in Israel using the new HAZUS-MH software: preliminary implementation. Geological Survey of Israel, Report GSI/11/2010, 33 pp.

Nakamura Y. (1988). On the urgent earthquake detection and alarm system (UrEDAS). In:

Proceedings of ninth world conference on earthquake engineering, Tokyo–Kyoto, Japan.

Peterson, J., (1993). Observations and modelling of background seismic noise. Open-file report

93-322, U. S. Geological Survey, Albuquerque, New Mexico.

Satriano, C., L. Elia, C. Martino, M. Lancieri, A. Zollo, and G. Iannaccone (2010). PRESTo, the

earthquake early warning system for southern Italy: Concepts, capabilities and future perspectives, Soil Dynam. Earthq. Eng. 31,

doi 10.1016/j.soildyn.2010.06.008. Wu Y.M., H. Kanamori (2005). Experiment on an onsite early warning method for the

Taiwan early warning system. Bull. Seism. Soc. Am. 2005; 95(1):347–53, doi:10.1785/0120040097.

44

Wald, D. J., V. Quitoriano, T. H. Heaton, and H. Kanamori (1999). Relationships between peak ground acceleration, peak ground velocity and modified Mercalli intensity in California, Earthq. Spectra 15, 557–564.

Zollo, A., O. Amoroso, M. Lancieri, Y. M. Wu, and H. Kanamori (2010). A threshold-based

earthquake early warning using dense accelerometer networks, Geophys. J. Int. 183, 963–974.

46

אדמה חלשות שאינ� גורמות נזקי . זו גישה המקובלת היו בקרב קבוצות עבודה ומחקר בתחו

ווא�, קליפורניה, איטליה, שוויי�) וקיימת עבורה ההתרעה לרעידות אדמה בעול (למשל, יפ�, טאי

תמיכת תוכנה בקהילה הבינלאומית.

ע השלמת , ויאפשר (גלי לח� ותאוצות ס!) הועדה ממליצה על פתרו� המשלב את שתי הגישות

תקבל בשלב הראשו� התרעה התרעה ממוקדת לכלל תושבי המדינה. המערכת שתיבנה ההתקנה,

בשלב התרעה ה. תאוצת ס! בגדר הסיסמית, ובהמש ג התרעה באמצעות גלי לח�המבוססת על

בלבד, והיא מצריכה למוסדות חינו תכוו� #העלולה לגרו להתרעות שווא אחדות בשנה –הראשו�

אלגוריתמי פשוטי יותר שנית� לייש בפרק הזמ� הנדרש בהחלטת הממשלה, ללא תוספת כספית

ידע הקיי בעול ויכולות בתחו הסיסמולוגיה של האג! הל מערכת תסתמ עה רבה.

שישולב בעתיד הקרוב ע המכו� הגיאולוגי במסגרת מינהל המחקר למדעי האדמה ,לסיסמולוגיה

הידע בתחו מערכות ההתרעה בעול . שיורחבתשופר ככל והי . המערכת

כות גבוהה לאור שני קוי באיחדשי סיסמומטרי 5מדי תאוצה ו 50כ מער הגילוי יכלול

. תחנות אלו ישולבו ע הרשת הסיסמית של מדורגי בסמיכות לבקע י המלח ולהעתק הכרמל

תשודרג לאות הרשת הקיימת .למע� כיסוי גיאוגרפי נרחב וניצול המשאבי הקיימי ישראל

סמי וה� שתשמש ה� לניטור סי אחת מערכתתהיה במדינת ישראל סטנדרטי , כ שבסיו ההקמה

ק"מ בכל קו והמרחק 10יהיה כ לאור ה"גדר הסייסמית" המרחק בי� תחנות סמוכות התרעה.ל

בשלב ייבנה , באזור הפחות מאוכלס, ק"מ. דרומית לי המלח 10בי� הקווי יהיה א! הוא כ

שליטה ובקרה מערכת .(עקב מגבלת תקציב) ק"מ בי� התחנות 10קו אחד ע מרווח של הראשו�

ותבצע ,תקלוט נתוני מכלל תחנות הרשת באמצעות תוכנות ייעודיות באג! לסיסמולוגיה, תוק

התרעה. ואבזמ� אמת אפיו� של כלל האירועי

למוסדות ימש שנתיי , ובסופו המערכת תחובר –המערכת תיבנה בשלושה שלבי : שלב ראשו�

ת, ייעשו בה שיפורי נדרשי , ובסופו ו תיבח� המערכמהלכימש כשנה, וב –שלב שני ;בלבד חינו

ביצועי ותדירות, רעידות אדמה חלשות הסתמ עלב מוסדות חינו .היא תהיה מבצעית עבור

ככל הנית� תו כדי ניצול הידע המערכת ייבדקו במש כל תקופת ההקמה ולאחריה, על מנת לשפר

. שלוש שני , המערכת תשודרג, מעבר ל –שלישי השלב ב וההתפתחות הטכנולוגית בתחו זה בעול

. במיקו גיאוגרפי שונה תחנות על פי הצור , ויוק מרכז שליטה ובקרה שני לגיבויבה וספו וית

ולאחר שתימצא אמינה בסטנדרטי המקובלי במערכות המתקדמות בעול ,המערכת תיבדק

אזרחי כלל ו גופי תשתית, היא תהפו למבצעית עבור ויצומצ המספר הצפוי של התרעות שווא

מלש"ח מעבר לתקציב הקיי 5לביצוע השלבי הראשו� והשני דרושה תוספת של כ .המדינה

מלש"ח. #7מלש"ח) ואילו לביצוע השלב השלישי יידרש תקציב נוס! של כ 15בהחלטת הממשלה (

למרות החריגות הללו ממסגרת התקציב, הועדה רואה חשיבות עליונה להקמת המערכת בהיק!

לשדרוג עתידי של מער התחנות ושיטות הגילוי, ולהקמת מערכת שליטה נוספת לגיבוי. המוצע,

יותקנו במוסדות שילוב יחידות התרעה מקומיות (ש :כוללי בי� השארנוספי שיפורי עתידיי

לצור קבלת תמונה , נזק משוערמפות יצור אוטומטי ומהיר של) ע המערכת הארצית, חינו

מערכות גילוי בשיטות נוספות, כגו� שילובבחדר המצב הלאומי בתו זמ� קצר, וראשונית של הנזק

GPS מערכת ההתרעה. ,בזמ� אמיתי ע

45

תקציר

על הקמת מערכת ,2012ביוני 7בישיבתה ביו ,החליטהועדת השרי להיערכות לרעידות אדמה

המשימה הוטלה על מינהל המחקר למדעי האדמה . התרעה קצרת מועד לרעידות אדמה בישראל

מית בעקבות ההחלטה הקי המינהל ועדת מומחי בינלאו. והי שבמשרד האנרגיה והמי

מידת ב ,שמטרתה לייע� למינהל ולהמלי� על המערכת האופטימלית שתענה על צרכי המדינה ותוק

הועדה כללה שלושה סיסמולוגי . פרק הזמ� ובגבולות התקציב עליה החליטה הממשלהב, האפשר

וחמישה סיסמולוגי , ל בעלי ש וניסיו� בהקמת מערכות התרעה לרעידות אדמה"מחו

להקמת שונות חלופות גישות ובחנה ו, חקר רעידות אדמהמישראל המתמחי בוגיאופיסיקאי

וסוגי , פיזור גיאוגרפי של המערכת, התרעההאלגורית , תרעההמבחינת צרכני ה, המערכת

.הנדרשי מכשירי ה

:חברי הועדה ה�

Prof. Richard M. Allen (Committee Chair), Director of the seismological laboratory, University of California, Berkeley, USA;

Dr. John Clinton, Director of seismic networks, Swiss Seismological Service, ETH, Zurich, Switzerland;

Prof. Aldo Zollo, Seismologist, University of Naples "Federico II", Italy;

גיאופיסיקאי, מנהל (בפועל), מינהל המחקר למדעי האדמה והי (מתא הועדה), ד"ר גדעו� בר

, גיאופיסיקאי, המכו� הגיאולוגיד"ר יריב חמיאל

, סיסמולוג, המכו� הגיאופיסיד"ר רמי הופשטטר

, סיסמולוג, המכו� הגיאופיסיד"ר ולדימיר פינסקי

, סיסמולוג, אוניברסיטת תל אביבד"ר אלו� זיו

מדידה מקומית יות להתרעה בפני רעידות אדמה. הראשונה מבוססת על קיימות שתי גישות עקרונ

(קו צפו! של תחנות לאור העתקי "גדר סיסמית" של תאוצת קרקע בשתי תחנות או יותר מתו

יוצרי רעידות האדמה), כ שהתרעה נשלחת א האות הנקלט גבוה מס! עוצמה מסוי שהוגדר

הול יחסית של מדי התאוצה הנדרשי להפעלתה. חסרונבפשטותה ובמחיר הז ואה ה. יתרונמראש

מהס! הנדרש להתרעה, נית� יהיה לבדוק אותה בס! עוצמות נמו יותרשאמנ בכ ואהשל השיטה

הפע הראשונה שבה היא תיבדק באופ� מבצעי תהיה ברעידה הגדולה אבל ,או על ידי סימולציות

התרעות יינתנו רק עבור ו� נוס! נובע מ� העובדה שחיסר. , או לחילופי� יתקבלו התראות שוואעצמה

ובמקרה של רעידות אדמה מרוחקות, למרות סבירות קרוב לתחנות הרשת, �שמוקד אדמה רעידות

תמיכת תוכנה היעדר נמוכה יחסית להתרחשות , לא נקבל התרעה נאותה. חסרו� בולט אחר הוא

יד ללא בעת התואפשרות לשדרג או לשפר אלמערכות מסוג זה בקהילה הבינלאומית, ולכ� לא תהיה

השקעה תקציבית משמעותית.

תחנות , אל S –מגלי ה , המהירי יותר(P-waves)גלי הלח� קליטתהגישה השנייה מבוססת על

בכל ותהצפוי תנודותסיסמית. ההתרעה מתקבלת על סמ חישוב עוצמת ומיקו הרעידה וההרשת ה

מכשור באיכות גבוהה יותר, א מאפשרת מת� התרעה מנ אנקודה באזור. גישה זו מצריכה

הזמ� באמצעות רעידות לאור דינאמי"), ובדיקה של המערכת שריג(" י ספציפיי אזורלממוקדת

47

המכון הגיאופיסי לישראל

: בישראל אדמה לרעידות מועד קצרת התרעה מערכת

ליישו� המלצות

5הופשטטר רמי, 4חמיאל יריב ,3קלינטו� ו�'ג, 2,4בר גדעו�, 1אל�. מ רד'ריצ

7זולו אלדו , 6זיו אלו�, 5פינסקי ולדימיר

ב"ארה, ברקלי, קליפורניה אוניברסיטת �1

והי� האדמה למדעי המחקר מינהל �2

שווי�, צירי�, ETH אוניברסיטת �3

הגיאולוגי המכו� �4

הגיאופיסי המכו� �5

אביב תל אוניברסיטת �6

איטליה, נאפולי אוניברסיטת �7

אדמה רעידות בפני להתרעה בינלאומית מייעצת ועדה

GII 500/676/12 GSI/26/2012

2012ירושלים, דצמבר

והמים האנרגיה משרד

יהגיאולוג המכון

Date post:	06-Jul-2020
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

Earthquake early warning for Israel: Recommended … · 2014-05-11 · Earthquake early warning for...

Documents