1. Andrew V. Newman, Abhijit Ghosh, Amanda Thomas, Grant T. Farmer, Jaime Convers Georgia Institute of Technology, Atlanta, GA, USA Interface Locking: Seismic and Geodetic Tools for Imaging Strain Accumulation Heather DeShon University of Memphis, TN, USA. Susan Schwartz University of California Santa Cruz, CA, USA. Edmundo Norabuena Instituto Geofisico del Peru, Lima, Peru. Timothy H. Dixon University of Miami, Miami, FL, USA.

2. 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

3. After initial location in 1D velocity model, events are relocated using 3D Vp, Vp/Vs from Deshon et al., 2006.

4. Cross-network relocations

5. -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)

6. Duration [s]

7. S. Stein and M. Wysession, 2003 Earthquake frequency-magnitude distribution Log 10 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

8. Wiemer et al., 2004 b-value distribution across an active fault (Parkfield segment of the San Andreas)

9. Schorlemmer et al., 2005 Parkfield event 2004

10. Spatial variation of b

11. Norabuena et al., 2004 Relation to geodetically derived locking

13. EPR CNS Interface mapping of b-value

14. 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., 2005 Newman et al., 2005

15. Duration [s] Global Seismic Hazards Assessment Program www.seismo.ethz.ch/gshap