HR: 14:55h
AN: T13E-06 INVITED     [Abstracts]
TI: Fault friction, afterslip and aftershocks
AU: Perfettini, H
EM: perfetti@lmtg.obs-mip.fr
AF: LMTG, Institut de recherche pour le D‚veloppement, Toulouse, 31400 France
AU: * Avouac, J
EM: avouac@gps.caltech.edu
AF: California Institute of Technology - Tectonics Observatory, 1200 E. California Blvd. MC 100-23, Pasadena, CA 91125 United States
AB: The spatio-temporal evolution of geodetic deformation and seismicity are key data that can be used to assess fault rheology at depth. From a review of some case examples for which geodetic data fault geometry and thermal structure is known we will discuss the physical parameters (fluids, lithology or temperature) controlling the extent of the seismogenic zone, characterized by rate-weakening friction. We then inctroduce the principle of the analysis from a simple 1-D model of stress transfer during the seismic cycle. Focusing then on the 1992 Landers earthquake we show that the observed posteismic deformation can be remarkably well predicted from a forward 3-D model in which co-seismic stress changes drive afterslip on the fault zone below the ruptured area, assumed to obey rate-strengthening frictional sliding (or equivalently brittle creep). We find A=dTo/dlnV= 0.6Mpa, where V is the sliding velocity and To and S are respectively the shear stress and normal stress on the creeping fault patch. This implies a value for A of the ~10-4 to 10-3, consistent with laboratory friction experiments. In the model, afterslip is initially focused below the fault patches with large co-seismic slip and then spreads laterally. The time evolution of geodetic deformation therefore results from both the decaying creep rate and from lateral spreading of the creeping zone. It results that the model departs somewhat from the prediction of the 1-D analytical solution. The model implies reloading of the seismogenic zone and can explain why about 90% of the aftershocks occurred within about 5km of the faults which ruptured during the main shock. The temporal evolution of aftershocks is also correctly predicted by the model.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: Fall Meeting 2005