Sequential Full-waveform Inversion of Refracted and Rayleigh Waves

This study presents advances in the elastic multi-parameter Full Waveform Inversion (FWI) for shallow seismic applications. Rayleigh waves are attractive for near surface characterisation since they exhibit a high signal to noise ratio in field data recordings and they are easily exited by using hammer blows. Rayleigh waves are highly sensitive to the S-wave structure of the subsurface. The FWI fails to reconstruct the P-wave velocity model due to its low effect on the Rayleigh waves which dominate the misfit. In order to properly incorporate the P-waves we initially perform a mono-parameter FWI of the refracted waves. This is followed by a multi-parameter inversion of the full wavefield. In a synthetic study we show that our new sequential approach is able to reconstruct more accurately the shallow P-wave velocity and to obtain a very good fit of the first arrivals. We further achieve an improved resolution of the shallow S-wave velocity and density structure.