HR: 10:50h
AN: S12B-03    [Abstracts]
TI: Quasistatic Fault slip on an Interface Separating Poroelastic Media With Different Diffusivity
AU: * Yamashita, T
EM: tyama@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AU: Suzuki, T
EM: suzutake@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AB: It is now widely believed that high-pressure fluid plays some role in the occurrence of slow earthquake rupture. Positive feedback between fluid pressure change and fault slip is required for the occurrence of such rupture as noted by Yamashita (2007). He theoretically studied the quasistatic fault slip on an interface separating dissimilar poroelastic media. He assumed difference only in the values of drained and undrained Poisson�fs ratios and their effects were examined. Although not clearly stated, he assumed that k/v is equal in the two media, where k is the permeability and v is the viscosity of fluid. We now theoretically study the effect of difference in the diffusivity. In other words, we assume that only the diffusivity is different in the two media. The fault behavior is studied using the boundary integral equation method (BIEM). We find that the fundamental solution is written in terms of single integrals of known functions, so that the numerical calculation can be carried out easily based on BIEM; here, the fundamental solution means the response from unit displacement discontinuity gradient. We first calculate the stress perturbation due to the sudden introduction of a finite 2-D in-plane fault. As observed in Yamashita (2007), the Coulomb failure stress begins to increase with time only at one of the fault tips, which may trigger unilateral quasistatic fault tip extension. The fault tends to extend in the direction of slip in the medium with higher diffusivity. This is largely due to the fluid flow enhanced near the fault tip. Although the increase in the Coulomb failure stress is larger for higher contrast in the diffusivity, there seems to exist an upper bound for the increase of the Coulomb failure stress. The increase in the Coulomb failure stress found in this study is generally larger than observed in the paper of Yamashita (2007). This suggests that spatial variation of diffusivity is more important for quasistatic fault slip due to fluid flow. The quasistatic fault extension is also simulated assuming the critical threshold value for the Coulomb stress.
DE: 7209 Earthquake dynamics (1242)
DE: 7260 Theory
DE: 7290 Computational seismology
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: 2007 Fall Meeting