HR: 0830h
AN: G21B-0269    [PDF]
TI: Influence of rheology and tectonic loading on postseismic creep
AU: * Mont\'esi, L G
EM: montesi@whoi.edu
AF: Woods Hole Oceanographic Institution, WHOI, Clark South 272D, MS24, Woods Hole, MA 02543-1542 United States
AB: Postseismic creep, as observed by GPS, indicates probably transient deformation of the lower crust or upper mantle triggered by earthquake-induced stress perturbations. In these regions, deformation can be localized on a frictional surface or on a ductile shear zone. These two hypotheses imply specific rheologies and therefore time dependence of postseismic creep. Hence, postseismic creep may constitute a probe into the rheology of aseismic regions of the lithosphere. I derive an analytical general relaxation law for a power law rheology which can be used to model postseismic creep in the absence of reloading of the proposed shear zone. The stress exponent, n, is diagnostic of the deformation mechanism. The rheology appropriate for frictional sliding produces a relaxation law similar to the power law case in the limit 1/n=0. GPS data following several earthquakes are adequately modeled using the generalized relaxation law. However, for at least three examples (1997 Kronotsky, 1999 Izmit, and 2001 Peru earthquakes), the inferred stress exponent is negative. Rather than the shear zone rheology, these negative exponents indicate that reloading of the shear zone by tectonic forces is important. Numerical simulations of postseismic deformation with non-negligible reloading produces curves that are well fit by the generalized relaxation laws with negative stress exponent, although the actual stress exponent of the rheology is positive. Although this prevents rheology from being well constrained by the studied GPS records, it is clear that reloading is important in the postseismic time interval. In other words, the stress perturbation induced by earthquake is not much larger than the ambient stress field.
DE: 1242 Seismic deformations (7205)
DE: 7209 Earthquake dynamics and mechanics
DE: 8010 Fractures and faults
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
SC: Geodesy [G]
MN: 2003 Fall Meeting