HR: 14:55h
AN: NS23A-06 INVITED    [Abstracts]
TI: Multi-Methods High-Resolution Seismic Imaging of Active Fault Zones
AU: * Catchings, R D
EM: catching@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Goldman, M R
EM: goldman@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Rymer, M J
EM: mrymer@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AB: Traditional methods of seismic imaging in active fault zones can be challenging because of large, abrupt velocity variations and disrupted strata within the fault zones. Such challenges are often more pronounced in the near surface, where accurate images are needed for trenching, ground-water evaluation, hazard evaluation, and other uses. We use a combination of seismic P- and/or S-wave refraction tomography and reflection imaging to characterize fault zones at scales ranging from a few meters to several kilometers. Most fault zones are characterized by reductions in P- and S-wave velocities ranging from about 10 to 35 percent, but in places with thin vadose zones or shallow water tables, these velocity anomalies may not be observed with P waves alone. To identify fault zones in such thin vadose-zone areas and in massive (non reflective) rocks, we use P- and S-wave data to develop images of Vp/Vs and Poisson's ratio, which are particularly sensitive to damaged rock. In addition to imaging the velocity anomalies, the detailed tomographic velocity models are used to accurately stack and migrate the reflection images. The combined velocity and reflection images can, therefore, define multiple characteristics of fault zones. In locations where borehole, trench, and other physical data are present, the combined seismic imaging method has been shown to be highly accurate. Comparison of the combined imaging method with traditional reflection imaging at various sites along the San Andreas other faults emphasizes the structural details added with the combined imaging method.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7250 Transform faults
DE: 8107 Continental neotectonics (8002)
DE: 8175 Tectonics and landscape evolution
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting