HR: 1340h
AN: S33C-1468    [Abstracts]
TI: Correlation of Static and Peak Dynamic Coulomb Failure Stress with Aftershocks, Seismicity Rate Change, and Triggered Slip in the Salton Trough
AU: Eddo, J
EM: jdeddo@gmail.com
AF: San Diego State University, 5500 Campanile Drive, San Diego, CA 92182,
AU: * Olsen, K
EM: kbolsen@sciences.sdsu.edu
AF: San Diego State University, 5500 Campanile Drive, San Diego, CA 92182,
AB: Numerous studies have found significant correlation of static Coulomb Failure Stress (sCFS, co-seismic earthquake induced stresses) with the occurrence of mainshocks, aftershocks, and triggered slip (e.g. Stein, 1999; Kilb, 2003; King et al., 1994, Arnadottir, 2003; Du et al., 2003; Freed, 2005). Static CFS estimates are primarily dependent on the final co-seismic slip distribution and fault geometry. Recently, complete or dynamic Coulomb Failure Stress, parameterized by its largest positive value (peak dCFS), has been proposed as an alternative triggering mechanism (Kilb, 2002). Peak dCFS estimates, in addition to the final slip dependence, have been shown to be strongly dependent on co-seismic source effects, such as rupture directivity (Kilb, 2002). However, most studies of stress transfer and earthquake triggering only incorporate sCFS and only a few studies have attempted to correlate seismicity rate change and triggered slip on surrounding faults. In this study we have modeled the distributions of sCFS and peak dCFS for four recent historical earthquakes (1968 M6.7 Borrego Mountain, 1979 M6.6 Imperial Valley, 1987 M6.6 Elmore Ranch, and M6.5 Superstition Hills) using a fourth-order staggered-grid finite-difference method, which incorporates anelastic attenuation, a 3-D velocity model, and heterogeneous slip distributions derived from strong ground-motion and geodetic inversions. The study area is 150 by 150 km located in the Salton Trough of the Imperial Valley, California. A cross-correlation is calculated between the modeled stresses and seismicity rate change in terms of the Z-value (Habermann, 1983) with a background seismicity rate removed. Modeling results show that peak dCFS provides significantly better correlation with aftershock distributions, seismicity rate change, and triggered slip than sCFS for all four events. Both sCFS and peak dCFS provide significant goodness of fit (>55%) with seismicity rate change up to a month after the mainshocks, with decreasing correlation for longer time periods. However, on average, the peak dCFS fits the seismicity rate change 26% better than sCFS for time periods up to a month after the mainshocks, and peak dCFS correlates with aftershocks significantly better than sCFS up to two years after the mainshock events. The overall favored performance of the peak CFS may be attributed to its strong sensitivity to rupture parameters in addition to the crustal velocity model and regional stress among other parameters. It should also be noted that the sensitivity to the coefficient of friction, poroelastic parameters, crustal velocity model, and regional stress, in terms of the goodness of fit with seismicity rate change, is stronger for peak dCFS (up to 20%), as compared to sCFS (up to 11%). Thus, peak dCFS appears as a more flexible triggering parameter as compared to sCFS. However, both sCFS and peak dCFS should be incorporated in studies of stress transfer and earthquake triggering, as they both appear to affect aftershock seismicity in a complementary way for some of the studied earthquakes.
DE: 1217 Time variable gravity (7223, 7230)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: 2007 Fall Meeting