Finite-Difference Modeling of Rayleigh Wave Scattering and P-SV(Lg) Coupling Problems

摘要

The work has focused on the effects on near-source heterogeneity upon seismic wave scattering and phase conversions. The basic tool was a developing 2-dimensional explicit linear finite-difference code. By use of various initial conditions and/or the principle of reciprocity. One can generate the teleseismic response of the Earth model to a general seismic source. The propagation of Pn/Sn/Rg phases with some Arctic paths are also modeled without using the principle of reciprocity. This FORTRAN-77 code has been run under the UNIX operating system on VAX, SUN, Convex, and Celerity computers. Rayleigh waves normally incident upon 2-D shallow heterogeneity are simulated by the linear finite-difference method to study attenuation, transmission, and reflection of Rayleigh waves and and to measure the Rayleigh-to-P and -SV body wave conversion. Transmission, reflection, and scattering depend on the depth, average scale size of the heterogeneity, and the amplitude of the spatial fluctuation of velocity. Linear finite-difference (FD) method was used to compare the excitation of far-field P-and SV-waves generated by shallow dilatational sources in a suite of heterogeneous 2-D crustal models. The crustal models tested included simple layered structures, media with random velocity perturbations having Gaussian or self-similar autocorrelation functions, media with rough or gentle topography generated by Markov chains, and laminated media with sinusoidal folds. The numerical experiments were conducted by directing a broadband planar P- or SV-wave with appropriate incidence angle upon the testing models. (jhd)