Direct Representation of Complex, High-contrast Velocity Features in Kirchhoff PreSDM Velocity Models

When velocity models are built for Kirchhoff pre-stack depth migration, complex, high-contrast features such as salt boundaries are usually represented explicitly during the model-building process. However, the migration algorithm typically requires a smoothed version of this velocity model in order to allow ray-based methods (ray tracing or an eikonal solver) to produce a stable modelled wavefield. The method presented in this paper incorporates high-contrast structural features directly into velocity models during migration, accounting correctly for the physics of wave propagation across these features. This has the potential to improve the fidelity of ray-based modelling, and to bring consequential improvements to the migrated image at complex, high-contrast features and to regions imaged through these features. There are also significant practical benefits for the Kirchhoff depth migration workflow due to the reduced size of migration velocity models and removal of the requirement for model sampling between model building and migration.