1. A Look Inside the San Andreas fault at Parkfield Through Vertical Seismic Profiling Chavarria, Malin, Catchings, and Shalev Science, 302, pp 1746-1748, 2003 Nick Schmerr April 9, 2007 ASU EarthScope Seminar

2. Event Migration Migrate data from 43 microearthquakes and 11 calibration shots to the Pilot Hole of the Vertical Seismic Profile array 3-component 15-Hz seismometers at 32 levels every 40 meters in depth from 200-1400 m below sea level (900- 1200 m below the surface) Chavarria et al., Science, 2003

3. Modified from Chavarria et al., Science, 2003

4. Kirchoff Migration detects scattering features Direct P and S muted to prevent interference with secondary arrivals P-P, P-P with conversions, S-S energy 7.5 s15 s Chavarria et al., Science, 2003

5. Results Chavarria et al., Science, 2003 Two secondary faults dipping to the NE at 2-3 km depth (a,b) Previously detected fault from SAFOD (d) Fault extending several km in depth (c) San Andreas Fault Zone

6. Results Chavarria et al., Science, 2003 Two secondary faults dipping to the NE at 2-3 km depth (a,b) Previously detected fault from SAFOD (d) Fault extending several km in depth (c) San Andreas Fault Zone

7. Chavarria et al., Science, 2003 Unsworth et al., Geology, 1997

8. Implications Scattering zone coincides with the location of low-resistivity along the SAFZ indicating the presence of fluid or altered materials The migration predicts SAFOD will pass through a previously unknown fault along the SAFZ Will help to improve structural models of SAFZ Additional Thoughts: Are all interfaces necessarily faults and cracks, or are they geologic contacts? How robust are the undiscussed interfaces?