3D elastic finite-difference modeling of seismic motion using staggered grids with nonuniform spacing

This article provides a technique to model seismic motions in 3D elastic me dia using fourth-order staggered-grid finite-difference (FD) operators impl emented on a mesh with nonuniform grid spacing. The accuracy of the propose d technique has been tested through comparisons with analytical solutions, conventional 3D staggered-grid FD with uniform grid spacing, and reflectivi ty methods for a variety of velocity models. Numerical tests with nonunifor m grids suggest that the method allows sufficiently accurate modeling when the grid sampling rate is at least 6 grid points per shortest shear wavelen gth. The applicability for a finite fault with nonuniform distribution of p oint sources is also confirmed. The use of nonuniform spacing improves the efficiency of the FD methods when applied to large-scale structures by part ially avoiding the spatial oversampling introduced by the uniform spacing i n zones with high velocity. The significant reduction in computer memory th at can be obtained by the new technique improves the efficiency of the 3D-F D method ale handling shorter wavelengths, larger areas, or more realistic 3D velocity structures.