Elastic P- and S-wave autofocus imaging with primaries and internal multiples

Abstract

Conventional seismic imaging methods rely on the single-scattering Born approximation, requiring the removal of multiply scattered events from reflection data prior to imaging. Additionally, many methods use an acoustic approximation, representing the solid earth as an acoustic (fluid) medium. We have developed imaging methods for (solid) elastic media that use primaries and internal multiples, including their PS and SP conversions, thus obviating the need for internal multiple removal and improving handling of internal conversions. Our methods rely on the elastic autofocusing method, which estimates full multicomponent elastodynamic Green’s functions from virtual sources interior to the medium to receivers placed on the surface. They require only surface seismic reflection data and estimates of the direct waves from virtual sources interior to the medium, both of which are commonly available at the imaging step of seismic processing. We tested our methods on a synthetic model with constant P and S velocities and vertical and horizontal density variations, by producing, for the first time to our knowledge, PP and SS images from elastic autofocusing that are compared to reference seismic images based on conventional methods. The effects of multiples are greatly attenuated in the images, with fewer spurious reflectors than are observed when using Born imaging.