HR: 08:00h
AN: S51D-01 INVITED     [Abstracts]
TI: Geophysical Characterization of Seismogenic Structures in Northern California
AU: * Thurber, C
EM: thurber@geology.wisc.edu
AF: UW-Madison, Geology and Geophysics 1215 W. Dayton St., Madison, WI 53706 United States
AU: Zhang, H
EM: hjzhang@geology.wisc.edu
AF: UW-Madison, Geology and Geophysics 1215 W. Dayton St., Madison, WI 53706 United States
AU: Langenheim, V
EM: zulanger@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Brocher, T
EM: brocher@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: In preparation for the centennial of the great 1906 San Francisco earthquake, we are developing a regional three-dimensional seismic wavespeed model for Northern California. The model will be used to compute strong ground motions in a simulation of the 1906 event and to help characterize both well-known and hidden seismogenic structures. The dataset combines P-wave arrival times from a well-distributed set of more than 6,000 earthquakes with a complete archive of available active-source P-wave travel times from the region. The wavespeed modeling is being carried out with a combination of conventional and double-difference seismic tomography. As a first stage, a preliminary model has been developed covering the region west of the Great Valley from Hollister to Clear Lake. The geometries of the major faults are clearly defined by the relocated seismicity, and most of the seismogenic faults are marked by significant wavespeed features. We take advantage of our high-quality wavespeed model and the abundant seismicity located with this model to examine the power of other geophysical observables to detect and characterize seismogenic faults in the region. Seismically active strike-slip faults with reasonable surface exposures predominate in the region, but we concentrate our analysis on faults or fault segments that are more challenging to characterize. We explore the degree to which gravity, magnetic, deformation, and topographic data, alone and in various combinations, can identify these seismogenic zones. For example, basement structures identifiable in the gravity and magnetic data (and in the wavespeed model) appear to control the seismicity associated with the Ortigalita fault (which runs through San Luis Reservoir), an unmapped strike-slip fault connecting the Calaveras and Greenville faults, and an apparent thrust fault on the edge of the Great Valley near Vacaville. We also investigate the degree to which active-source seismic data alone can resolve structural features associated with these faults. Our findings can provide some guidance for geophysical studies of faults in areas with more limited seismicity and seismic networks.
DE: 8180 Tomography
DE: 8015 Local crustal structure
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting