HR: 0800h
AN: S21B-0554    [Abstracts]
TI: Unified Understanding of Dynamic Earthquake Rupture in Terms of Thermoporoelastic Effects
AU: * Suzuki, T
EM: suzutake@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, the University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AU: Yamashita, T
EM: tyama@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, the University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AB: We theoretically study 2-D dynamic earthquake rupture taking account of thermoporoelastic effects including fluid flow and inelastic porosity change; the porosity on the fault is assumed to increase inelastically with increasing fault slip. We found in the analysis of a 1-D fault model that a single nondimensional parameter Su controls the system behavior [Suzuki and Yamashita, 2007]; the slip-weakening and -strengthening behavior appeared when Su is less and greater than a critical value, respectively. The case 0<Su<1 is found to be excluded from the consideration because rock melting is expected. Since the case Su=0 was already analyzed in Suzuki and Yamashita [2006], we assume Su>1 in this study. Since the reduction in stress drop is larger for a larger slip for Su>1 as found in Suzuki and Yamashita [2007], the stress drop reduction is larger at fault patch further behind the extending fault tips in 2-D fault model. This can successfully simulate a pulse-like fault slip [e.g., Heaton, 1990] as actually simulated in our 2-D analysis. In addition, the maximum slip velocity in our fault model does not change much with crack tip extension, which differs from expected from the classical Griffith crack model. It is also reported in some studies that the radiation efficiency estimated seismologically exceeds unity for some earthquakes, which contradicts its definition. This paradox can be solved if we assume a relatively large Su value for these earthquakes as suggested by Suzuki and Yamashita [2007], which is actually confirmed here by numerical simulation of 2-D fault model. Seismic moment in such case is smaller than that in the classical crack model. This occurs because the slip- strengthening becomes dominant some time after the slip onset. The intensity of the stress at the crack tips in our model is therefore smaller than that in the classical crack model. In addition, there is no strong dependence of the stress drop on the crack length. This suggests that the growth of crack is more easily arrested by a spatial heterogeneity of strength distribution when Su>1.
DE: 5114 Permeability and porosity
DE: 5120 Plasticity, diffusion, and creep
DE: 7209 Earthquake dynamics (1242)
DE: 7260 Theory
SC: Seismology [S]
MN: 2007 Fall Meeting