Scattering of elastic waves in geometrically anisotropic random media and its implication to sounding of heterogeneity in the Earth's deep interior

Abstract

The scattering features of elastic waves in media with geometrically anisotropic heterogeneities are investigated in terms of scattering attenuation, coda level and scattering directivity. The theoretical variation of scattering attenuation with normalized wavenumber (ka) is formulated using the multiple forward scattering and single backscattering approximation. Estimates obtained from numerical simulations agree with the theoretical predictions well. The level of scattering is influenced by the anisotropy (aspect ratio, direction) and the wave incidence direction. The scattering level is not sensitive to the scale variation in the wave incidence direction, but is highly sensitive to the scale variation in the tangential direction. Forward scattering is dominant when waves are incident along the major direction of geometrically anisotropic heterogeneity, and backward scattering is dominant when the waves are incident in the minor direction. The scattered energy is not distributed isotropically in media with anisotropic heterogeneity, and the level of early coda varies with the wave incidence angle. The late coda is composed of multiscattered and multipathing waves, and displays a stochastically stable energy level. The incidence angle of waves is a key parameter in the early coda variation, and an approach with classified seismic data for incidence angle is desired in the study of anisotropic heterogeneity in Earth's deep interior from seismic coda and precursor.