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)

Duration [s]

S. Stein and M. Wysession, 2003

Earthquake frequency-magnitude Earthquake frequency-magnitude distributiondistribution

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.

Gagnon et al., 2005Newman et al., 2005

Duration [s]

Global Seismic Hazards Assessment Program

www.seismo.ethz.ch/gshap