HR: 1330h
AN: T52A-0250    [PDF]
TI: New Insights on Stress Rotations From a Forward Regional Model of the San Andreas Fault System Near its Big Bend in Southern California
AU: * Fitzenz, D D
EM: fitzenz@usgs.gov
AF: USGS, MS 977 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Miller, S A
EM: miller@erdw.ethz.ch
AF: Geophysics Institute ETHZ, ETH Hoenggerberg, Zurich, 8093 Switzerland
AB: Understanding the stress field surrounding and driving active fault systems is an important component of mechanistic seismic hazard assessment. We develop and present results from a time-forward 3-dimensional model of the San Andreas Fault system near the Big Bend in Southern California. We assess the model boundary conditions by comparing model and observed tectonic regimes, and explore the forward model of earthquake generation along these fault segments to target measurable properties. We investigate how slip along the faults perturbs stress orientations, and how stress orientations may allow inferences on the stress state. We use a quasi-static fault model [Fitzenz and Miller, 2001], where GPS-constrained tectonic loading drives faults modelled as viscoelastic bodies embedded in an elastic half-space [Fitzenz and Miller, 2003] mostly sealed from the surrounding rocks and subjected to ductile compaction and shear creep. We show that a transpressive tectonic regime develops southwest of the model Big Bend as a result of the loading boundary conditions and migrates toward the Bend due to slip along the model fault. Stress transfer from fault slip is shown to transiently induce significant perturbations in the local stress tensors (where the slip profile is very heterogeneous). These result in off-fault tectonic regimes and optimal orientations for faulting that differ from those generally prevailing in the area around the faults. These transient perturbations in the local stress field then disappear when subsequent model earthquakes smoothen the slip profile. Maps of maximum shear stress show artificial stress concentrations near the bend, and emphasize that future models should include a more continuous representation of the model faults. When no material weakness is considered, results show that hydrostatically pressured intact rock is very difficult to break from the loading boundary conditions.
DE: 7209 Earthquake dynamics and mechanics
DE: 7260 Theory and modeling
DE: 8150 Plate boundary--general (3040)
DE: 8168 Stresses--general
SC: Tectonophysics [T]
MN: 2003 Fall Meeting