High Resolution Multi-Modal Surface Wave Inversion for Shallow S-Wave Velocity Model Building

Shallow S-wave velocity model building is very important for land and Ocean Bottom Seismic PS data processing. Surface waves, propagating along the near surface, provide useful information for shallow S-wave velocity estimation. In this study, multi-modal surface wave inversion (MM-SWI) was used to build a high resolution shallow S-wave velocity model for a recently acquired Ocean Bottom Node survey. Super gathers were constructed to improve the signal-to-noise ratio and the spatial resolution of surface wave dispersion spectra. Auto-picking of multi-modal dispersion curves was then implemented. To overcome the strong nonlinear problem during multi-modal inversion, the combined Levenberg-Marquard and differential evolution method was used. High resolution dispersion analysis and robust auto-picking improved productivity significantly, which allowed for a high resolution shallow S-wave velocity model to be built in time. The inverted MM-SWI model correlates well with both the shallow geological structures and the seafloor map. It reveals fine layers, small faults, small channels and other lithological variations. The MM-SWI model was used for PS statics correction and also incorporated into the S-wave velocity model building process. Results from the model comparison, statics application and the PS depth image support the reliability of high resolution shallow S-wave velocity models from MM-SWI.