HR: 13:55h
AN: G53A-02 INVITED    [Abstracts]
TI: InSAR Measurements of Postseismic Deformation due to the Mojave Desert Earthquakes: Implications for the Driving Mechanisms
AU: * Fialko, Y
EM: yfialko@ucsd.edu
AF: UCSD, 9500 Gilman Dr, La Jolla, CA 92093-0225, United States
AB: The 1992 Landers and 1999 Hector Mine earthquakes in the Eastern California Shear Zone have initiated robust postseismic transients that were used to study the rheology of the Earth's crust and upper mantle. I will present measurements of postseismic deformation due to both earthquakes derived from InSAR observations. A continuous imaging of the earthquake area by the European Space Agency ERS-2 satellite (including recent acquisitions in the Zero Gyro Mode) produced 7-year long timeseries of deformation for the Hector Mine, and 15-year-long timeseries of deformation for the Landers earthquake. A comparison of the InSAR data collected in the post-Landers and post-Hector Mine epochs indicates that the surface patters of postseismic deformation are very similar, implying a common mechanism. For both events the data reveal lobes of the radar range changes predominantly to the west of the respective earthquake ruptures. The lobes have a characteristic wavelength of a few tens of kilometers, and amplitude of several centimeters. High gradients in the radar range changes across the faults are suggestive of a shallow source of deformation. The data demonstrate that the post-Landers transient has persisted for more than 10 years after the earthquake. A number of different mechanisms has been proposed to explain the observed time-dependent deformation, including afterslip, viscous-like response of a substrate below the brittle-ductile transition, and re-distribution of pore fluids in the upper crust. For non-linear (e.g., powerlaw) rheologies, the surface deformation field may be indistinguishable from that due to afterslip at the early stages of relaxation, when the deformation is localized in high stress areas on the downdip continuation of the earthquake fault. However, at later stages of relaxation visco-elastic models predict appreciable changes in the displacement pattern. In particular, vertical velocities may change sign after viscous flow in the ductile substrate becomes more diffuse. No such reversal is observed in case of the Landers - Hector Mine sequence. Fluid flow and poro-elastic effects are incapable of explaining the observed horizontal deformation, but may substantially contribute to vertical postseismic motions, further complicating a discrimination between afterslip and visco-elastic relaxation.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
SC: Geodesy [G]
MN: 2007 Fall Meeting