Migration velocity analysis and imaging for tilted TI media

Abstract

Tilted transversely isotropic (TTI) formations cause serious imaging distortions in active tectonic areas (e.g., fold‐and‐thrust belts) and in subsalt exploration. Here, we introduce a methodology for P‐wave prestack depth imaging in TTI media that properly accounts for the tilt of the symmetry axis as well as for spatial velocity variations. For purposes of migration velocity analysis (MVA), the model is divided into blocks with constant values of the anisotropy parameters ε and δ and linearly varying symmetry‐direction velocity VP0 controlled by the vertical (kz) and lateral (kx) gradients. Since tilt is not well constrained by P‐wave data, the symmetry axis is kept orthogonal to the reflectors in all trial velocity models. The MVA algorithm estimates the velocity gradients kz and kx and the anisotropy parameters ε and δ in the layer‐stripping mode using a generalized version of the method introduced by Sarkar and Tsvankin for factorized VTI (TI with a vertical symmetry axis) media. Synthetic tests confirm the robustness of our MVA methodology and show that ignoring the influence of tilt may lead to significant image distortions and errors in parameter estimation. The ability of our MVA algorithm to separate the anisotropy parameters from the velocity gradients can also be used in lithology discrimination and geologic interpretation of seismic data in complex areas.