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 receivers. The purpose of this study is to investigate multi‐component applications of interferometry for processing OBC data. This translates into using interferometry to retrieve pseudo‐source data on the sea bed containing not only PP‐, and PS‐wave reflections, but also SS‐wave reflections and sea‐bed surface waves (Scholte 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 vertical 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 property for these conversions, particularly for generating pure‐mode SS‐wave reflections.