HR: 14:10h
AN: G22D-03    [PDF]
TI: The seismic cycle on intracontinental megathrusts
AU: * Avouac, J
EM: avouac@gps.caltech.edu
AF: Caltech, California Boulevard, Pasadena, CA 91125 United States
AU: Perfettini, H
AF: Caltech, California Boulevard, Pasadena, CA 91125 United States
AU: Bollinger, L
AF: Caltech, California Boulevard, Pasadena, CA 91125 United States
AU: Beyssac, O
AF: Ecole Normale Superieure, rue Lhomond, Paris, 75252 France
AB: Our understanding of the mechanics that relates crustal deformation and seismicity remains crude. The "seismic cycle" concept does provide some useful and physically sound rationale, but many basic questions remain open. To state a few: What proportion of crustal deformation is taken up by large earthquakes? How co-seismic deformation does relates to stress and strain accumulated since the last large earthquake having ruptured the same fault? What mechanism drives aftershocks and background seismicity in the interseismic period? Is interseismic straining a stationary process? These questions are addressed here from investigations focused on some major intracontinental thrust faults in the Himalayas and Taiwan. In such settings, the analysis of the fault geometry and properties at depth are facilitated by the shallow dip angles and also because deep rocks are ultimately brought to the surface providing a way to assess thermal conditions at depth. These case examples provide insight on the factors, and associated physical processes, which control the geometry and mechanical behavior of the fault portion capable of producing larges earthquakes (such as the 1999 M=7.6 Chichi, in Taiwan, or the 1934, M=8.5, Bihar-Nepal earthquakes). The thermal structure is a key factor because it determines the transition with depth from a locked seismogenic fault portion, to a zone undergoing predominantly strain strengthening brittle creep, and finally to a zone of aseismic ductile flow at depth. Some simple model is derived that can be used to analyze jointly seismicity rate and crustal strain in the interseismic period and during post-seismic relaxation, and assess the possibility for non-stationary straining in the interseismic period.
DE: 7209 Earthquake dynamics and mechanics
DE: 8102 Continental contractional orogenic belts
SC: Geodesy [G]
MN: 2003 Fall Meeting