HR: 0800h
AN: G11A-0762 INVITED     [Abstracts]
TI: Investigating the mechanics of the seismic cycle along plate boundaries
AU: * Avouac, J
EM: avouac@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California MC 100-23 Divison of Geological and Planetary Sciences, Pasadena, CA 91125 United States
AU: Perfettini, H
EM: perfetti@geologie.ens.fr
AF: Laboratoire de Geologie Laboratoire de G‚ologie Laboratoire de G‚ologie Laboratoire de G‚ologie, Ecole Normale Superieure 24 rue Lhomond, F-75005 PARIS, Cedex 5 France AU: Chlieh, M
EM: chlieh@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California MC 100-23 Divison of Geological and Planetary Sciences, Pasadena, CA 91125 United States
AB: The seismic cycle concept offers a convenient kinematic framework to integrate geodetic and geological observations. Generally the integration is made through elastic dislocation modeling, eventually based on Savage's backslip model. This sort of kinematic description is valid insofar as there is no permanent strain accumulating off the main fault zone. This approximation applies well to subduction zones and strike-slip faults but can also be applied to orogenic contexts providing some caution regarding the modeling of vertical displacements. The kinematic description of strain over the seismic cycle in orogenic contexts such as the Himalaya or Taiwan seems to make sense in view of the rheology of continental rocks and it dependence on temperature. In this context the thermal structure might be the key factor determining the transition with depth from a seismogenic fault portion obeying rate-weakening friction, where motion is presumably dominantly stick-slip, to a zone undergoing predominantly strain strengthening brittle creep, which slip steadily during the interseismic period or produce transient afterslip in the postseismic period, and finally to a zone of aseismic ductile flow at depth. For subduction zone the physical factors for the variations with depth of fault properties is more enigmatic. In particular, the fact that the plate interface generally creeps at depth below about 50km does cannot be easily explained by thermally enhanced ductility nor by serpentinization of the mantle wedge. Some simple model of stress transfers during the seismic cycle is used to analyze jointly seismicity rate and crustal strain in the interseismic period and during post-seismic relaxation. We show that reloading of the upper brittle crust, due to postseismic afterslip and viscous relaxation is a viable mechanism to explain jointly geodetic data and the decay rate of aftershocks. This is substantiated by the analysis of a few cases such as the Chi-Chi 1999 earthquake, or the 2001 Peru earthquake. The model is also used to assess the possibility of non-stationary strain in the interseismic period. It turns out that depending on the viscosity and thickness of the viscous shear zone at depth stress transfer during the seismic cycle may induce significant variation of interseismic strain that could be measured from geodetic techniques, and explain possible discrepancies between geological slip rates and geodetic slip rates.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8123 Dynamics, seismotectonics
DE: 8159 Rheology--crust and lithosphere
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting