Multi-mode Inversion for P-wave Velocity and Thick Near-surface Layers

In seismic data for hydrocarbon exploration, the near surface is often a major source of wavefield distortion, reducing the quality of the image at the exploration target level. Adequate knowledge of shallow subsurface P-wave velocities and layer thicknesses allows to mitigate these distortions. Dispersion curves can be used to estimate near-surface properties. However, the fundamental mode of the Rayleigh wave is not sensitive to P-wave velocities and has only a limited penetration depth. I show that considering higher modes in the inversion allows to reconstruct subsurface models with thick shallow layers. Furthermore, the higher modes also resolve the P-wave velocities. Higher modes are included in an error norm based on the Wronskian. This has as additional benefit that there is no need to know the number of the mode a pick belongs to. I show the improvement over using only the fundamental mode both on synthetic data as well as field data from Oman.