Depth imaging in strongly heterogeneous VTI media

Abstract

In this paper, we apply the one‐way dual‐domain wave propagators for the transversely isotropic media with a vertical symmetry axis (VTI) (Han and Wu, 2003a; Han and Wu, 2003b) to the imaging problem in such media. The one‐way propagator is used to perform both 2‐D poststack and prestack depth migration with a synthetic qP‐wave field in complex VTI media. The propagator is derived from an approximate dispersion relation of a scalar qP‐wave equation. It propagates in a homogeneous VTI background medium in the wavenumber domain and calculates the effect of velocity and anisotropy perturbations in the spatial‐domain. This research includes testing the ability of the propagator for imaging a qP‐wave field in media with strong anisotropy and complex structures, and the capability of the propagator for accurately propagating large angle waves. The effect of anisotropy on image quality is examined. The SEG/EAEG Salt model is modified from isotropic media to VTI media, while keeping its original velocity distribution and complex structures. Good quality images from both poststack imaging and prestack imaging support its validity and accuracy for imaging complex media with strong perturbations and strong anisotropy. When imaging the same anisotropic data, isotropic algorithms produce poor quality images with background artifacts, improperly focused energy and mispositioned reflectors, and may introduce false reflectors.