A practical implementation of converted-wave reflection full-waveform inversion

Depth imaging of converted-wave (P-to-S) ocean-bottom seismic (OBS) data requires a depth model for both the P- and S-wave velocities. Building the S-wave velocity model is very challenging: conventional techniques include PP and PS image registration, or joint PP and PS tomography. These approaches are often impeded by the lack of a reliable PS image in the shallow part of the model due to the sparse-receiver acquisition of typical OBS surveys, and have limited resolution to deal with complex lateral velocity variations. We introduce a new full-waveform inversion technique to update the S-wave velocity using converted-wave reflection data recorded in the radial component of OBS surveys. Key aspects of the method include the use of acoustic Born-modeling, a robust objective function to handle kinematic and dynamic differences, and a layer-stripping strategy to simplify the non-linearity of the inversion problem. The proposed approach is validated on different synthetics, and demonstrated on a field data example, giving an improved S-wave velocity and better reflector continuity for PS imaging.