Abstract
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.
10.1126/science.1090711
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