Time-migration Tomography based on Reflection Slopes in Pre-stack Time-migrated Seismic Data

The accuracy of migration velocity estimation is critical for seismic imaging. Historically, ray-theory based approaches to migration-velocity estimation have been widely used in the industry. However, these approaches may be quite time consuming for a variety of reasons, e.g., event picking, extensive computation of ray-tracing results, total iteration turn-around time, etc. We present an efficient approach to estimation of a velocity model for time migration. As input, we use reflection slopes belonging to a pre-stack time-migrated seismic data set, which has been migrated using a preliminary (initial) velocity model. The slopes are derived using the gradient structure tensor method. We apply a fast migration velocity estimation loop, which combines kinematic de-migration, kinematic migration and linearized inversion for the parameters of the migration velocity model. The iteration scheme is based on minimizing the offset slope in the time-migration domain. The approach can be generalized for use in the depth domain, if supplemented by appropriate time-to-depth mapping techniques.