HR: 11:05h
AN: G12A-04 INVITED     [Abstracts]
TI: Spatio-temporal Signatures of Post-seismic Relaxation due to the Mojave Desert (S. California) Earthquakes from InSAR and GPS Data, With Implications for the Driving Mechanisms
AU: * Fialko, Y
EM: fialko@radar.ucsd.edu
AF: IGPP, SIO, UCSD, La Jolla, CA 92093 United States
AB: The 1992 $M_w7.3$ Landers and 1999 $M_w7.3$ Hector Mine earthquakes in the Mojave desert (southern California) produced some of the best ever documented post-seismic deformation transients. I use a well-populated catalog of the Synthetic Aperture Radar (SAR) data from the ERS 1 and 2 satellites that includes more than 200 interferable acquisitions, and time series from several tens of Global Positioning System (GPS) stations to investigate the spatial and temporal characteristics of the post-seismic deformation following the two earthquakes. The post-Landers geodetic data reveal a deformation transient with a characteristic relaxation time of several years. The stacked InSAR data show prominent lobes of post-seismic relaxation with a characteristic wavelength of 30-40 km, and amplitude of $\sim$5 cm along the satellite line of sight (LOS). The LOS displacements exhibit high gradients across the surface trace of the Landers rupture, implying a shallow origin of the relaxation process. The spatio-temporal signatures of the post-Landers InSAR data are consistent with percolation of pore fluids in the upper crust in response to the co-seismic stress changes imposed by the Landers earthquake. The observed time dependence of post-seismic response implies effective hydraulic diffusivity of the order of $0.1-1$ m$^2$/s, consistent with laboratory, borehole, and field measuremets. This conclusion is confirmed by data from several boreholes in the near field of the Landers rupture that show gradual changes in the water level over a time period of 2-3 years following the Landers earthquake. Pore fluid flow, however, underpredicts horizontal displacements in the far field, suggesting a contribution of another deformation mechanism, such as the deep afterslip or visco-elasto-plastic relaxation. Models assuming pure visco-elastic behavior of the lower crust and upper mantle imply that the deformation is still essentially transient several years following the earthquakes, and predict that significant post-seismic deformation is yet to occur in the future.
UR: http://sioviz.ucsd.edu/$\sim$fialko/res\_land.html
DE: 8107 Continental neotectonics
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8160 Rheology--general
DE: 7205 Continental crust (1242)
DE: 7209 Earthquake dynamics and mechanics
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting