Dynamical fault rupture processes in heterogeneous media

Abstract

The fault rupture processes in a horizontally layered medium and also in a three-dimensionally heterogeneous structure are investigated on three-dimensional, spontaneous dynamic shear crack models. The wave equations for three-dimensional space are solved numerically by a finite difference scheme under the appropriate boundary conditions and the finite stress fracture criterion. The heterogeneous properties of the elastic medium, particularly the existence of low-velocity zones, give remarkable effects on the rupture process, yielding appreciably decelerated rupture velocities and large fault displacements in and around the zones and strong motions in the near-field. The large fault displacements are enhanced when the rupture breaks the ground surface. The static seismic moment in the case with a low-velocity zone is essentially the same as in a homogeneous half-space. An attempt is made to simulate the rupture process of a moderate-size earthquake, by applying the above shear crack model in a heterogeneous medium with depth-dependent and laterally heterogeneous stress drop. The model appears to explain the observed features to a satisfactory degree.