HR: 0830h
AN: NG41B-0060    [PDF]
TI: Generation of fault damage zone: Modeling and simulation of dynamic off-fault damage
AU: * Ando, R
EM: ando@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, 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, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Based on observations of fault rocks, the typical structure of natural fault zone is constituted by a very localized slip plane and a widely distributed damage zone, fractured by shear deformation, around the slip plane in the direction of the fault normal. However, the generation process of the damage zone is still an open question. On the seismological viewpoint, investigation of the effect of the damage zone on a dynamic rupture process is important for the understanding of the complexity of earthquakes. In the present study, we consider the generation of fault damage zone associated with a dynamic rupture. We assume an in-plane shear fault called main fault in a 2-D homogeneous isotropic elastic medium. We also assume a large number of preexisting micro weak-planes around the main fault as the model of fractures in the earth's crust; shear ruptures are permitted to trigger on them. As the initial phase of our study, we simply assume that the ruptures propagate only on the pre-existing planar weak-planes that are parallel to each other. In our result, we observe that width of the zone containing the triggered micro weak-planes becomes wider as the main fault propagates; triggering of the micro ruptures propagates by S-wave speed b caused by the wave radiation from the main fault. These micro ruptures are considered to be the fault damage zone in natural fault cases. We also observed that an accelerated rupture on the main fault decelerated in the initial stage of the dynamic propagation, and then the rupture velocity of the reaccelerated propagation does not reach the limiting speed that is Rayleigh-wave speed (0.92b in our case). These decelerations are caused by negative interactions due to a stress shadow of the off-fault micro ruptures. In conventional macroscopic fault models, the thickness of faults is neglected. In such a case, the ruptures are aligned in coplanar and only positive interactions, which accelerate the each rupture, are affected. However, as shown in the present microscopic study, when we consider the thickness on the fault as the fault damage zone, the negative interactions are affected, which are never appeared in the macroscopic modeling and are important to the rupture process.
UR: http://www.eri.u-tokyo.ac.jp/ando/agu
DE: 3210 Modeling
DE: 3220 Nonlinear dynamics
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics and mechanics
DE: 7260 Theory and modeling
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting