Abstract

Tilted transversely isotropic (TTI) formations cause severe imaging problems in active tectonic areas (e.g., fold-and thrust-belts) and in subsalt exploration plays. 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
?and
?having 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
?and
?in the layer-stripping mode. We have also performed synthetic tests on different models like syncline, thrust-sheet etc., having tilted layers to confirm the robustness of our MVA algorithm. This shows that by ignoring the influence of tilt may lead to significant image distortions and errors in the parameter estimation. The ability of our MVA algorithm to separate the anisotropy parameters from velocity gradients can also be used in lithology discrimination and geologic interpretation of seismic data in complex areas.