AN OPTIMAL ABSORBING BOUNDARY-CONDITION FOR FINITE-DIFFERENCE MODELING OF ACOUSTIC AND ELASTIC-WAVE PROPAGATION

This paper presents an optimal absorbing boundary condition designed t o model acoustic and elastic wave propagation in two-dimensional and t hree-dimensional media using the finite difference method. In this con dition, extrapolation on the artificial boundaries of a finite differe nce domain is expressed as a linear combination of wave fields at prev ious time steps and/or interior grids. The acoustic and elastic reflec tion coefficients from the artificial boundaries are derived. They are found to be identical to the transfer functions of two cascaded syste ms-the inverse of a causal system and an anticausal system. The method makes use of the zeros and poles of reflection coefficients in a comp lex plane. The optimal absorbing boundary condition described in this paper yields, on the average, reflection coefficients about 10-dB smal ler than Higdon's absorbing boundary condition, and about 20-dB smalle r than Reynolds' absorbing boundary condition.