HR: 1340h
AN: S23A-0294    [Abstracts]
TI: Time-dependent evolution of stress over the past 200 years in Southern California
AU: * Ali, T
EM: stali@purdue.edu
AF: Department of Earth and Atmospheric Sciences, 550 Stadium Mall Drive, Purdue University, West Lafayette, IN 47907 United States
AU: Freed, A M
EM: freed@purdue.edu
AF: Department of Earth and Atmospheric Sciences, 550 Stadium Mall Drive, Purdue University, West Lafayette, IN 47907 United States
AU: B\"{u}rgmann, R
EM: burgmann@seismo.berkeley.edu
AF: Department of Earth and Planetary Science, 389 McCone Hall, University of California, Berkeley, CA 94720 United States
AB: Seismic hazard estimates can be refined by examining the current state of stress change in regions prone to earthquakes. Active faults which have not recently failed and lie in regions experiencing high rates of stress increase represent the best candidates for near future earthquakes. Evolution of stress in the crust is influenced by three main factors: interseismic loading, static stress changes from large earthquakes; and postseismic relaxation of a viscous lower crust or upper mantle. Southern California has had more than eighteen large $(M_{w} \geq 6.5)$ earthquakes in the past two centuries. Previous research has calculated the evolution of stress in southern California over this period of time due to coseismic slip associated with these events and interseismic loading. Here we extend this analysis to include the effects of viscous relaxation that follows each quake and can significantly alter the stress field. Our approach is to numerically model the evolution of Coulomb stress for southern California due to all the major $(M_{w} \geq 6.5)$ earthquakes over the past 200 years using the superposition of a viscoelastic model and the regional stress rate. The regional stress rate is due to the relative motion of the Pacific and North American plates as constrained by the SCEC velocity field map. We plan to present results that discuss where Coulomb stress is currently building the fastest and how these stress changes resolve themselves on major strike-slip faults in the region and thrust faults within the LA Basin. We are particularly interested in how the stress shadows (region of Coulomb stress decrease) cast by the great Fort Tejon earthquake of 1857 and other large historic events have been influenced by the competing role of viscoelastic relaxation, which would tend to prolong the longevity of shadows associated with strike-slip earthquakes, and the build up of regional stresses which work to erase them.
DE: 7223 Seismic hazard assessment and prediction
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2004 AGU Fall Meeting