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Subsalt imaging at the Thunder Horse Field in the Gulf of Mexico is challenging primarily because the salt canopy, overlying roughly 75% of the structure, greatly distorts subsalt illumination and causes imaging and resolution problems. Since the Thunder Horse discovery, advancements in seismic acquisition techniques and imaging technologies have significantly improved subsalt images. The latest successful application is from a tilted transverse isotropy (TTI) reverse time migration (RTM) project combining two wide azimuth towed streamer (WATS) data sets and three narrow azimuth towed streamer (NATS) data sets. The addition of an extra WATS data set and the application of the recent imaging technologies are key contributors to the dramatic structural image improvements with better defined three-way events and a higher signal-to-noise ratio (S/N).

A more detailed velocity analysis is required for successful pre-stack depth migration model building and tomographic methods offer a potential solution. However, migration velocity analysis is often a underdetermined problem. We present a new finite-offset depth tomography scheme that overcomes the problems of non-linearity and allows us to perform automatic dense velocity analysis in structurally complex areas were classical linear methods fail. We demonstrate the advantage of the new tomography scheme on a deep offshore Gulf of Mexico dataset from the Green Canyon area.