HR: 09:00h
AN: G21D-05 INVITED    [Abstracts]
TI: Influence of velocity strengthening regions on the seismic cycle: Implications for postseismic slip and the generation of slow earthquakes.
AU: * Perfettini, H
EM: hugo.perfettini@ird.fr
AF: IRD, OMP.14 av E. Belin., Toulouse, 31400, France
AU: Ampuero, J
EM: ampuero@erdw.ethz.ch
AF: ETH Zurich.Institute of Geophysics. Seismology and Geodynamics Group, ETH Honggerberg HPP O13.1, Zurich, CH-8093, Switzerland
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: California Institute of Technology. Tectonics Observatory., 1200 E. California Blvd, Pasadena, CA 91125, United States
AB: Postseismic slip is thought to be located in velocity strengthening (VS) regions which promotes stable slip. Deep afterslip is observed following large earthquakes, and occurs in such a VS zone, the fragile-ductile transition zone also named brittle creep fault zone (BCFZ). Superficial afterslip is sometimes observed and may represent the relaxation of VS patches embedded in the seismogenic fault zone (SFZ). Slow earthquakes are now widely reported and appear to be located in the upper part of the BCFZ. However, the link between those events and postseismic slip is not obvious and we present here a model that may reconcile those observations. We study the response of a rate and state strengthening fault to static Coulomb stress changes. If the size of the fault is larger than a characteristic length Lb, a slip transient could be generated, Lb being analogous to the nucleation length of a velocity weakening fault. A positive Coulomb stress step induces a slip transient followed by a relaxation similar to the case of a pure velocity strengthening region. This slip transient may escape from detection because it occurs right after the onset of perturbation and could be misinterpreted as part of the main perturbation (e.g., rupture of the mainshock). Unlike what one could expect, a negative perturbation in Coulomb stress also generates a slip transient. The main difference with the positive Coulomb stress step is that the transients corresponding to unloading steps are of smaller amplitude and occurs way after the onset of perturbations, and could be misinterpreted as a ‘spontaneous' creep burst. Postseismic slip corresponds to the response of a VS zone to a large scale positive Coulomb stress change while spontaneous slow earthquakes may correspond to the response of a VS zone to a localized negative Coulomb stress change. The implications of our results in terms of geodetic slip inversions and numerical modelling of the seismic cycle will also be briefly discussed. Influence of velocity strengthening regions on the seismic cycle: Implications for postseismic slip and the generation of slow earthquakes.
DE: 0545 Modeling (4255)
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Geodesy [G]
MN: 2007 Fall Meeting