HR: 1340h
AN: T53B-1429    [Abstracts]
TI: Probing Fault Properties Using Post-Seismic InSAR Observations and Finite Element Modeling of the Mw 7.1 Hector Mine Earthquake
AU: * Cochran, E S
EM: ecochran@ucsd.edu
AF: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego 9500 Gilman Ave., MC 0225, San Diego, CA 92093 United States
AU: Peltzer, G
EM: peltzer@ess.ucla.edu
AF: University of California, Los Angeles, Earth and Space Sciences 595 Charles Young Dr., Los Angeles, CA 90095 United States
AU: Peltzer, G
EM: peltzer@ess.ucla.edu
AF: Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AB: Complex post-seismic displacement signals are observed with InSAR following the 1999 Mw 7.1 Hector Mine rupture. Along its northern section, a left step in the Lavic Lake fault and a change in fault orientation with respect to the direction of rupture produce local co-seismic compression. Full resolution interferometric pairs covering up to two years after the mainshock show the effects of poroelastic relaxation both within and around the main fault zone. A large zone of subsidence is observed in the step-over, abruptly bounded to the east by the Lavic Lake fault. In addition, an approximately 200 m-wide zone of subsidence can be followed along the fault, north and south of the main subsiding zone. These features are interpreted as the poroelastic response of the shallow crust to the co-seismic stress change, as the pore fluid pressure gradients dissipate after the event. We construct an 11-epoch time series of surface displacement maps from 4 days to 2 years following the mainshock. The observed subsidence rate appears to decrease exponentially after the earthquake with apparent relaxation times of less than 1 year. The post-seismic response within the fault zone occurs at a faster rate and produce a larger subsidence (>2 cm) than in the country rock adjacent to the fault. These observations suggest that the 200 m-wide fault zone has higher porosity or greater water saturation than the rock outside the fault. We use the finite element program FEMLAB to model the post-seismic poroelastic relaxation process within and around a fault. The model uses a water-saturated porous volume of rock and a fault of finite width with different material properties. A fully coupled poro-elastic solution is computed at time steps after an initial compression, mimicking the co-seismic stress change. Such a model, constrained using InSAR time series observations, provides a novel way of probing fault properties.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 5114 Permeability and porosity
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: Fall Meeting 2005