HR: 1340h
AN: S13B-1309    [Abstracts]
TI: Effect of 3D Stress Heterogeneity on Aftershock Sequences
AU: * Smith, D E
EM: desmith@ucr.edu
AF: University of California, Riverside, Department of Earth Sciences, Institute of Geophysics and Planetary Physics University of California, Riverside, Riverside, CA 92521, United States
AU: Dieterich, J
EM: dieterichj@ucr.edu
AF: University of California, Riverside, Department of Earth Sciences, Institute of Geophysics and Planetary Physics University of California, Riverside, Riverside, CA 92521, United States
AB: Observations of spatially varying slip along fault zones and in earthquakes suggest that both slip and stress are spatially heterogeneous and possibly fractal in nature. We model seismicity in spatially heterogeneous stress fields, including the temporal response to static stress perturbations. Starting with 3D models of the crust with fractal-like heterogeneous stress, we add a stress perturbation due to a major earthquake, and couple this system to rate-state seismicity equations to explore the temporal evolution of seismicity during an aftershock sequence. We find that the stress perturbation can generate an increased focal mechanism orientation scatter and a sizable rotation of the average P-T orientation. Both of these effects have been observed in the real Earth. Previous models (without 3D stress heterogeneity) assumed these effects reflected "real" changes in the stress orientation, and hence required small background differential stresses of 10 MPa or less to satisfy the observations. In our model, the presence of stress heterogeneity can bias the failures, creating an apparent stress rotation much larger than the actual stress rotation. Consequently, our model can generate rotations similar to that observed in the real Earth with background differential stresses in the range of 20-50 MPa. We also explore how the focal mechanism orientations rotate and scatter throughout the aftershock cycle. Woessner (2005), observed a step increase in focal mechanism orientation scatter at the onset of a major earthquake with a decay back to smaller scatter during the aftershock sequence. Using rate and state friction seismicity rate equations, we model this temporal evolution of seismicity in our 3D heterogeneous stress volumes.
DE: 3265 Stochastic processes (3235, 4468, 4475, 7857)
DE: 4440 Fractals and multifractals
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8164 Stresses: crust and lithosphere
SC: Seismology [S]
MN: 2007 Fall Meeting