In recent years, it has become the standard practice in deep water Gulf of Mexico (GOM) to perform seismic imagingassuming tilted transverse isotropy (TTI) symmetry to describe the anisotropic effects of wave propagation in salt-withdrawalmini-basins. When compared to isotropic and vertical transverse isotropic (VTI) imaging, TTI prestack depth imaginggenerally provides flatter common image gathers (CIGs) for wide azimuth data, improves image focusing, and significantlyreduces well/seismic mis-ties. This anisotropy is thought to arise from the geometry of sedimentation processes, with the“tilt” applied by subsequent tectonic activity. However, the presence of significant tectonic stress or uneven stress can causefractures in thin-bed layers, which results in a further directional velocity variation for seismic wave propagation, orazimuthal anisotropy around the bed normals. In these cases, the transverse isotropic assumption is insufficient to explainconflicting residual moveouts among CIGs of different azimuths from TTI imaging. A more general anisotropic model, tiltedorthorhombic (TOR), is needed to cope with azimuthal velocity variation in these complex geological settings.In this paper, we apply TOR model building and migration to an area in the Green Canyon area of central GOM with the aimof improving the subsalt image. Two orthogonal GOM surveys, one narrow azimuth towed streamer and one wide azimuthtowed streamer, are used to derive both TTI and TOR models. With the TOR model, we observe improved gather flatnessamong azimuths, better well ties, and improved salt imaging - all of which lead to more accurate delineation of saltgeometries and, consequently, better imaging beneath the salt. We infer that tilted orthorhombic provides better arepresentation of an overburden with fractures and uneven stress. Through improved overburden velocities, TOR reverse timemigration produces better subsalt images.
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