Numerical modeling of elastic wave scattering by near-surface heterogeneities

Abstract

A perturbation method for elastic waves and numerical forward modeling are used to calculate the effects of seismic wave scattering from arbitrary shape shallow subsurface heterogeneities. Wave propagation is simulated using elastic finite difference for several earth models with different nearsurface characteristics. The near-surface scattered wavefield is modeled by separating the incident wavefield from the total wavefield by means of a perturbation method. We show that the scattered field is equivalent to the radiation field of an equivalent elastic source excited at the scatterer locations. The scattered waves consist mostly of body waves scattered to surface waves and are, generally, as large as, or larger than, the reflections. The results indicate that the scattered energy depends strongly on the properties of the shallow scatterers and increases with increasing impedance contrast, increasing size of the scatterers relative to the incident wavelength, and decreasing depth of the scatterers. Also, sources deployed at depth generate weaker surface waves, whereas deep receivers record weaker surface and scattered body-to-surface waves.