2D isotropic elastic Gaussian-beam migration for common-shot multicomponent records

Abstract

Gaussian-beam migration (GBM) is flexible and adaptable for imaging geologically complicated areas. It avoids some limitations, such as amplitude singularity in caustic zones and an inability to image multiple arrivals, of traditional ray-based migration approaches. Previous studies on GBM mainly focused on acoustic media. We have developed a 2D isotropic elastic GBM scheme for common-shot multicomponent records. Our method extrapolates P- and S-mode wavefields simultaneously using the Kirchhoff-Helmholtz integral solution of the isotropic elastodynamic equation. We separate the extrapolated wavefields into compressional and shear modes using the Helmholtz decomposition, and we then implement a modified dot-product imaging condition. This approach enables us to produce clear PP-images and avoid polarity reversal issues for PS-images. In addition, based on the theory of wavefield approximation in the effective vicinity of central rays, we derive a formula to compute the propagation angles of paraxial rays, which can be used to extract angle-domain common-image gathers.