HR: 16:45h
AN: G14A-04    [Abstracts]
TI: Crustal Deformation Along the Northern San Andreas Fault System From Geodetic and Geologic Data
AU: * Murray, M H
EM: mhmurray@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, Univ. of California, Berkeley, CA 94720-4760 United States
AB: The San Andreas fault system north of the San Francisco Bay area is composed of three sub-parallel right-lateral faults: the San Andreas, Rodgers Creek-Ma'acama, and Green Valley-Bartlett Springs. The San Andreas has been essentially aseismic since it last ruptured in 1906, and no major historical earthquakes have occurred on the more seismically active Ma'acama and Bartlett Springs faults, although the slip deficit on the Ma'acama fault may now be large enough to generate a magnitude 7 earthquake. Since 2002, we have been collecting GPS measurements at about 80 monuments that form roughly 10-station profiles across the northern San Andreas fault system from Pt. Reyes to Cape Mendocino. Most of the monuments were last observed in 1993 or 1995, so the new observations significantly improve estimates of their relative motion and models of average interseismic strain accumulation, including possible spatial variations along the fault system. We use angular velocity-backslip block modeling to determine a self-consistent northern California deformation field and rates of strain accumulation along the northern San Andreas fault system. Preliminary results from our modeling, which includes 2 blocks within the San Andreas fault system, as well as a Sierran-Great Valley block, and the Pacific and North America plates, show agreement between observed and predicted velocities at less than 2 mm/yr. Fault-parallel deformation across the entire San Andreas fault system is 38 mm/yr, but deep slip rates on the sub-parallel faults are poorly constrained due to significant correlations between the deep slip rates and locking depths, which we fully characterize using Monte Carlo techniques. We use Bayesian techniques to combine the GPS observations with constraints derived from other seismic, geodetic, and paleoseismic observations, such as locking depths, surface creep rates, and inferred geologic slip rates. These additional constraints significantly improve the estimates of the slip rates and locking depths on the faults, allowing better assessment of seismic hazards along the northern San Andreas fault system.
DE: 7223 Seismic hazard assessment and prediction
DE: 8107 Continental neotectonics
DE: 1206 Crustal movements--interplate (8155)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting