Seismic wave propagation and scattering in heterogeneous crustal waveguides using screen propagators: ISH waves

The great advantages of one-way propagation methods, such as the generalize d screen propagators (GSP) method, are the fast speed of computation, often several orders of magnitude faster than the full-wave finite difference an d finite element methods, and the huge savings in internal memory. In this article, a halfspace GSP is formulated for the SH half-space problem. Two v ersions of the halfspace GSP are derived: the wide-angle pseudo-screen and the phase-screen. The Moho discontinuity is treated as parameter perturbati ons from the crustal background, The validity and limitations of this treat ment are discussed. It is shown that half-space screen propagators can accu rately propagate guided crustal waves that are composed of small-angle wave s with respect to the horizontal direction. Comparisons of numerical result s with a wavenumber integration method for flat crustal models and a finite difference algorithm for heterogeneous models show excellent agreements. F or a model with propagation distance of 250 km, dominant frequency at 0.5 H z, the GSP method is about 300 times faster than a finite difference algori thm with a similar accuracy. These comparisons demonstrate the accuracy and efficiency of the method. We apply our method to simulate regional wave pr opagation in different types of complex crustal waveguides including those with small-scale random heterogeneities. The influence of these heterogenei ties on Lg amplitude attenuation and Lg coda formation is significant.