Elastic FWI of multi-component ocean-bottom seismic to update shear-wave velocity models

Elastic full-waveform inversion (FWI) is now emerging as an industrial tool for the compressional velocity (Vp) model build, driven mainly by diving and reflected P waves. On the other hand, the inversion of S waves in elastic FWI to update shear velocity (Vs) models is more challenging due to the limitations of data acquisition and reduced sensitivity of surface seismic to Vs. In this paper, we propose a practical methodology for low-wavenumber Vs updates by elastic FWI, driven mainly by converted waves in multi-component ocean-bottom seismic data. The first key step of our methodology builds a high-quality Vp model from elastic Vp FWI using the hydrophone and vertical geophone data. The second key step is the use of horizontal geophones to reconstruct the low wavenumbers of the Vs model from the kinematics of the converted waves. We show a field application of our approach highlighting improved PS reverse time migration (RTM) imaging, and better consistency with the PP RTM, coming from the elastic Vs FWI. In addition, a Vs update from a Born-based PS-reflection FWI method also shows a good PS RTM uplift, although the elastic FWI model generated the better PS RTM image.