Attenuating Pseudo S-waves in Acoustic Anisotropic Wave Propagation

Abstract

The importance of anisotropy in seismic imaging has been recognized for several decades. In recent years, a growing number of anisotropic applications of reverse time migration (RTM) and full waveform inversion (FWI) have attempted to account for anisotropic effects of the real-world subsurface physics. In anisotropic media the P-wave, SV-wave, and SH-wave are intrinsically coupled, therefore the media are elastic in nature. However, the elastic anisotropic wave equation is computationally demanding and requires S-wave velocity model, for which in practice we often have little information. Consequently, the acoustic assumption is widely used in seeking anisotropic wave equations. Stable acoustic anisotropic wave equations may create apparent pseudo S-waves during wave simulation. S-wave contributions then show up as artifacts in migrated images from RTM and in velocity perturbations from FWI. We propose a model taper method to eliminate the source generated S-wave, and derive a series of approximate formulae that allow accurate and efficient attenuation of pseudo S-waves after acoustic anisotropic wave propagation, as a supplementary routine. Synthetic data and real data examples are shown to verify the proposed prescription in complex media.