HR: 1340h
AN: S13B-0199    [Abstracts]
TI: Seismicity rate vs. distance from strike-slip faults in southern California
AU: * Powers, P
EM: pmpowers@usc.edu
AF: University of Southern California, Dept. of Earth Sciences 3651 Trousdale Pkwy., Los Angeles, CA 90089-0740 United States
AU: Jordan, T
EM: peter_powers@yahoo.com
AF: University of Southern California, Dept. of Earth Sciences 3651 Trousdale Pkwy., Los Angeles, CA 90089-0740 United States
AB: We use three high resolution catalogs (Hauksson[2003], Shearer[2003], and SCSN) and detailed fault representations of the SCEC Community Fault Model (CFM) to constrain seismicity rates perpendicular to strike-slip faults in southern California. Using a stacking process for earthquakes in regions proximal to major, linear fault segments, we find that the cumulative number of earthquakes a~d^-γ where d is distance from a fault and γ=0.85ñ0.05. We verified our result by stacking across multiple spatial and magnitude ranges with various normalization methods. This value holds out to 7-8km from a fault, beyond which 'background' seismicity dominates. Stacking across increasing lower-magnitude cutoffs indicates that b-value remains constant away from a fault and that b~1. On the basis of this result, we hypothesize that aftershocks of an earthquake away from a fault should be biased towards and along the fault. To test this hypothesis, we filter our fault segment sub-catalogs for mainshock-aftershock sequences using reasonable time and distance windows and stack them on the mainshocks in 2km wide bins away from the fault. Stacks of various mainshock magnitude ranges (within a M2.5 - 4.5 range) show that aftershocks are biased towards faults. This result compares well with a model that couples our seismicity-distance scaling relation with the observation that earthquake aftershock density d~r^-2 where r is distance from a mainshock. These data suggest that we can improve seismic triggering models by incorporating finer details of the relationship between seismicity and fault structure.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8010 Fractures and faults
DE: 8123 Dynamics: seismotectonics
SC: Seismology [S]
MN: Fall Meeting 2005