Robust surface-wave full-waveform inversion

Estimation of subsurface seismic properties is important in civil engineering, oil & gas exploration, and global seismology. We present a method and an application of robust surface-wave inversion in the context of 2D elastic waveform inversion of an active-source onshore dataset acquired on irregular topography. The lowest available frequency is 5 Hz. The recorded seismograms at relatively near offsets are dominated by dispersive surface waves. In exploration seismology, surface waves are generally treated as noise (“ground roll”) and removed as part of the data processing. In contrast, here, we invert surface waves to constrain the shallow parts of the shear wavespeed model. To diminish the dependence of surface waves on the initial model, we use a layer-stripping approach combined with an envelope-based misfit function. Surface waves are initially inverted using short offsets (up to 0.6 km) and over a high-frequency range (12.5–15 Hz) to constrain the shallow parts of the model. The lower-frequency components and longer offsets, which can sample deeper parts of the model, are gradually added to the process as the inversion proceeds. At the final stage, surface waves are inverted using offsets of up to 1.5 km over a band between 5–15 Hz. The final V_s model includes high-resolution features in the near surface, and shows good agreement with results from dispersion-curve analysis. The data fit is also greatly improved.