HR: 1330h
AN: T52A-0246    [PDF]
TI: Constraints on the mechanics of the Southern San Andreas fault system from GPS velocity and stress
AU: * Becker, T W
EM: tbecker@igpp.ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, University of California San Diego, IGPP-0225, 9500 Gilman Drive, La Jolla, CA 92093 United States
AU: Hardebeck, J L
EM: jhardebeck@usgs.gov
AF: United States Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, CA 94025 United States
AU: Anderson, G
EM: ganderso@gps.caltech.edu
AF: United States Geological Survey, 525 South Wilson Avenue, Pasadena, CA 91106 United States
AB: We use Global Positioning System (GPS) derived velocities and stress-orientations to study the distribution of long-term slip on the system of faults comprising the southern California plate boundary region. Of particular interest is how slip is partitioned over multiple earthquake cycles between the San Andreas Fault (SAF), the San Jacinto Fault (SJF) and the Eastern California Shear Zone. Some prior paleoseismologic and geodetic work places the majority of slip on the SAF. Other studies, however, find that the SJF accommodates about half of the slip in the south, implying half as much slip on the San Bernardino segment of the SAF. Two new data sets are used to further constrain the mechanics of the SAF. The first is the Southern California Earthquake Center's geodetic velocity field version 3 (Shen et al., 2003), which includes much improved coverage over prior models. The second is a regional map of stress field orientations at seismogenic depths, as determined from an inversion of earthquake focal mechanisms. While GPS data has been used in similar studies, this is the first application of stress field observations to this problem. We construct a simplified version of the southern California fault system, and model the surface velocities using a block model with elastic strain accumulation, following Meade et al. (2002). Additionally, we model the stress orientations at seismogenic depths, assuming that the stress field results from the loading of active faults. An inversion for fault slip rates is performed to simultaneously fit the GPS and stress observations. The model fit to the data is good in general, indicating that a simple mechanical model can capture both observed interseismic strain and stress accumulation. We evaluate the sensitivity of the slip rate solutions to the different datasets and identify "anomalous" fault segments with stresses that deviate from our simple loading model.
DE: 1208 Crustal movements--intraplate (8110)
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 8150 Plate boundary--general (3040)
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting