HR: 16:15h
AN: S14B-02    [Abstracts]
TI: Influence of Rupture Speed on Effective Normal Stress Changes During Slip Between Dissimilar Poroelastic Materials
AU: * Dunham, E M
EM: edunham@fas.harvard.edu
AF: Dept. Earth Planet. Sci., Harvard Univ., Cambridge, MA 02138, United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Dept. Earth Planet. Sci. and Sch. Engin. Appl. Sci., Harvard Univ., Cambridge, MA 02138, United States
AB: We consider the poroelastic response of a fault zone consisting of a relatively impermeable fault core surrounded by a more permeable damage zone. In-plane slip compresses one side of the fault and extends the other, generating a gradient in fluid pressure that drives flow across the fault. Any asymmetry across the fault, either in elastic properties and density measured over the scale of the rupture, or in poroelastic properties and permeability measured over the hydraulic diffusion length (as would occur if slip localizes at the boundary between the fault core and damage zone), leads to effective normal stress changes on the fault [Rudnicki and Rice, 2006]. The sign of the effective normal stress change reverses if the rupture propagates in the opposite direction, in a manner similar to the well-known bimaterial effect of normal stress changes during slip between dissimilar elastic solids. The sign of the effective normal stress change cannot always be predicted solely from the contrast in elastic properties across the fault. In numerical models with opposing elastic and poroelastic effects, we observe, as the rupture accelerates, a reversal in the sign of effective normal stress change from that predicted by the local poroelastic mismatch to that predicted by the larger scale elastic mismatch, provided that the wave-speed contrast exceeds about 5--10% (the precise value depends on the poroelastic contrast and Skempton's coefficient). For faults separating more elastically similar materials, there exists a minimum poroelastic contrast above which the poroelastic effect always determines the sign of the effective normal stress change, no matter the rupture speed.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7290 Computational seismology
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: 2007 Fall Meeting