Automatic Top-salt Refinement Using RTM Time-shift Gathers

We present a method for automatically obtaining a detailed, accurate representation of a top-salt velocity model contrast, starting from a crude initial top-salt interpretation. The method is based on the analysis of time-shift gathers obtained in a salt-flood velocity model with RTM. It uses the fact that source- and receiver-side wave fields back-scattered at the velocity contrast during the RTM process result in an image contribution in time-shift gathers that interferes at the reflection point with the image contribution due to the incident wave fields. The time-shift value at, or directly above, the top-salt interface at which back-scattering of the source- and receiver-side wave fields occurs is automatically picked. The resulting time shifts are filtered and converted into a detailed depth update of the top salt horizon. The process is repeated until convergence. We demonstrate the method on a 2D synthetic data example with a complex top-salt interface.