Andrew V. Newman, Abhijit Ghosh, Amanda Thomas, Andrew V. Newman, Abhijit Ghosh, Amanda Thomas, Grant T. Farmer, Jaime Convers Grant T. Farmer, Jaime Convers Georgia Institute of Technology, Atlanta, GA, USA Georgia Institute of Technology, Atlanta, GA, USA Interface Locking: Seismic and Interface Locking: Seismic and Geodetic Tools for Imaging Strain Geodetic Tools for Imaging Strain Accumulation Accumulation Heather DeShon Heather DeShon University of Memphis, TN, USA. University of Memphis, TN, USA. Susan Schwartz Susan Schwartz University of California Santa Cruz, CA, USA. University of California Santa Cruz, CA, USA. Edmundo Norabuena Edmundo Norabuena Instituto Geofisico del Peru, Lima, Peru. Instituto Geofisico del Peru, Lima, Peru. Timothy H. Dixon Timothy H. Dixon University of Miami, Miami, FL, USA. University of Miami, Miami, FL, USA.
Transcript
Andrew V. Newman, Abhijit Ghosh, Amanda Thomas, Andrew V. Newman, Abhijit Ghosh, Amanda Thomas, Grant T. Farmer, Jaime ConversGrant T. Farmer, Jaime Convers
Georgia Institute of Technology, Atlanta, GA, USAGeorgia Institute of Technology, Atlanta, GA, USA
Interface Locking: Seismic and Interface Locking: Seismic and Geodetic Tools for Imaging Strain Geodetic Tools for Imaging Strain AccumulationAccumulation
Heather DeShonHeather DeShonUniversity of Memphis, TN, USA.University of Memphis, TN, USA.
Susan SchwartzSusan SchwartzUniversity of California Santa Cruz, CA, USA.University of California Santa Cruz, CA, USA.
Edmundo NorabuenaEdmundo NorabuenaInstituto Geofisico del Peru, Lima, Peru.Instituto Geofisico del Peru, Lima, Peru.
Timothy H. DixonTimothy H. DixonUniversity of Miami, Miami, FL, USA.University of Miami, Miami, FL, USA.
12/99 –06/2001 - 20 land (18 mo) - 14 OBS (1st 6 mo) Mw=6.4 Outerrise EQ occurred just
after OBS recovered. Main-shock and aftershocks were poorly located by our network
Nicoya-CRSEIZE
Analysts:
(UCSC) - self (postdoc) - Heather DeShon (Grad) - Matt Densmore (UG) - Martin Valle (Grad) - Megan Avants (UG) - Dev Gobalkrishnan (UG) - Christina Bernot (UG)
(OVSICORI) - Victor González - Marino Protti
(GT) - Abhijit Ghosh (Grad) - Amanda Thomas (UG) - Alice Koerner (UG) - Jaime Convers (Grad) - Grant Farmer (UG/Grad)
>10,000 regional events located
After initial location in 1D velocity model, events are relocated using 3D Vp, Vp/Vs from Deshon et al., 2006.
Cross-network relocations
- Remove crustal events
- Define normal to a priori surface
- Select minimum cylinder containing n (35) events
- bin results normal to parabola
- Determine new 3D position from only maximum seismicity bin
Interface Modeling (maximum seismicity method):
By minimizing error associated with poor locations, it should well approximate interface <~40 km depth (intra-slab events deeper)
Log10 N = a – b M M = Magnitude N = # earthquakes > M a = activity (y-
intercept) b = slope
• b-value: ratio of number of smaller to larger earthquakes
• b-value global average ~1– 10x more events with unit M
decrease– high b-value: more small
earthquakes– low b-value: more larger
earthquakes
Wiemer et al., 2004
bb-value distribution across an active fault -value distribution across an active fault (Parkfield segment of the San Andreas)(Parkfield segment of the San Andreas)
Schorlemmer et al., 2005
Parkfield event 2004Parkfield event 2004
Spatial variation of Spatial variation of bb
Norabuena et al., 2004
Relation to geodetically derived Relation to geodetically derived lockinglocking
Relation to geodetically derived Relation to geodetically derived lockinglocking
EPR
CNS
Interface mapping of Interface mapping of bb-value-value
Direct measurements of shallow locking:
Intensive Ocean-bottom seismic and geodetic deployments near at risk regions are needed to characterize seismicity and strain accumulation.
