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Science 5 December 2003:
Vol. 302. no. 5651, pp. 1746 - 1748
DOI: 10.1126/science.1090711
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Reports

A Look Inside the San Andreas fault at Parkfield Through Vertical Seismic Profiling

J. Andres Chavarria,1* Peter Malin,1 Rufus D. Catchings,2 Eylon Shalev1

The San Andreas Fault Observatory at Depth pilot hole is located on the southwestern side of the Parkfield San Andreas fault. This observatory includes a vertical seismic profiling (VSP) array. VSP seismograms from nearby microearthquakes contain signals between the P and S waves. These signals may be P and S waves scattered by the local geologic structure. The collected scattering points form planar surfaces that we interpret as the San Andreas fault and four other secondary faults. The scattering process includes conversions between P and S waves, the strengths of which suggest large contrasts in material properties, possibly indicating the presence of cracks or fluids.

1 Division of Earth and Ocean Sciences, Nicholas School of Environment and Earth Sciences, Duke University, Box 90227, Durham, NC 27708, USA.
2 U.S. Geological Survey, MS977, 345 Middlefield Road, Menlo Park, CA 94025, USA.

* To whom correspondence should be addressed. E-mail: jac4{at}duke.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Orientation of Three-Component Geophones in the San Andreas Fault Observatory at Depth Pilot Hole, Parkfield, California.
V. Oye and W. L. Ellsworth (2005)
Bulletin of the Seismological Society of America 95, 751-758
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