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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
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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
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Modified from Chavarria et al., Science, 2003
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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
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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
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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
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Chavarria et al., Science, 2003 Unsworth et al., Geology, 1997
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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?
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