Elastic Interferometry for OBC Data - Theory and Examples

Abstract

Elastic imaging from ocean bottom cable (OBC) data can be challenging because it requires the prior estimation of both P- and shear-wave (S-wave) velocity fields. Seismic interferometry is an attractive technique for processing OBC data because it performs model-independent redatuming; retrieving "pseudo-sources" at the positions of the re-ceivers. The purpose of this study is to investigate multicomponent applications of inter-ferometry for processing OBC data. This translates into using interferometry to retrieve pseudo-source data on the sea bed containing PP-, PS-, and possibly SS-waves. We discuss perturbation-based, elastic interferometry with synthetic and field OBC datasets. Conventional and perturbation-based interferometry integrands computed from a synthetic are compared to show that the latter yields little acausal response and fewer artifacts. A 4C (Xx, Xz, Zx and Zz) pseudo-source response retrieves pure-mode SS-reflections as well at PP- and PS-reflections. Pseudo-source responses observed in OBC data are related to P-wave conversions at the seabed rather than to true horizontal or ver-tical point forces. From a Gulf of Mexico OBC dataset, principal components of a 9C pseudo-source response demonstrate that Vp/Vs at the seabed is an important factor in the conversion of P to S for obtaining the pure-mode SS-wave reflections.