COMPOSITE ABSORBING BOUNDARIES FOR THE NUMERICAL-SIMULATION OF SEISMIC-WAVES

Composite absorbing boundary methods are developed for the numerical s imulation of seismic waves. These methods combine low-angle absorbing boundary conditions, based on the characteristic analysis of one-dimen sional wave equations, with either of two novel wave field modificatio n approaches, namely the anisotropic filters and the one-way sponge fi lters. The anisotropic filter method adjusts the propagation direction of the waves, so that they reach the boundary at normal angles. The o ne-way sponge filter method endows the transition zone with a dissipat ion mechanism that selectively damps the incoming waves. These methods absorb not only the body waves but also the surface waves. A narrow t ransition zone adjacent to a computational boundary is introduced whos e width is smaller than in the sponge filter approach. Numerical examp les illustrate the effectiveness of these methods in absorbing the art ificial reflections.