A 2.5-D Time-Domain Elastodynamic Equation For Plane-Wave Incidence

Abstract

SUMMARY Full 3-D modelling of seismic wave propagation is still computationally intensive. Recently, as a compromise between realism and computational efficiency, two-and-ahalf-dimensional (2.5-D) methods for calculating 3-D elastic wavefields in media varying in two dimensions have been developed. Such 2.5-D methods are an economical approach for calculating 3-D wavefields, and require a storage capacity only slightly larger than those of the corresponding 2-D calculations. In this paper, a 2.5-D elastodynamic equation in the time domain is constructed for seismic wavefields in models with a 2-D variation in structure but obliquely incident plane waves. The approach does not require wavenumber summation, and as a result requires much less computation time than in previous techniques. The modelling of such seismic wavefields for a 2.5-D situation with an incident plane wave is of considerable practical importance: for example, this approach can be applied to the modelling of the local response of an irregular basin structure, or to teleseismic body waveforms from shallow earthquakes occurring in subduction zones, where the laterally heterogeneous medium can have a large effect on the waveform. All the variables in the 2.5-D time-domain elastodynamic equation are real-valued, so the propagation characteristics can be efficiently calculated using 2-D time-domain numerical techniques such as the finite-difference method or the pseudospectral method with less computation time and memory than for other implementations.