Abstract
We present a dispersion-inversion method which inverts for the P-velocity model from guided waves propagating in wave guides of arbitrary geometry. Its misfit function is the squared summation of differences between the predicted and observed dispersion curves of guided P waves, and the inverted result is a high-resolution estimate of the near-surface P-velocity model. We denote this procedure as wave-equation dispersion inversion of guided P waves (WDG), which is valid for near-surface waveguides with irregular layers and does not require a high-frequency approximation. It is more robust than full waveform inversion and can sometimes provide velocity models with higher resolution than wave-equation traveltime tomography. Both the synthetic-data and field data results demonstrate that WDG for guided P waves can accurately invert for complex P-velocity models at the near surface of the Earth.
In this paper, we present the theory for wave-equation inversion of guided Pwaves, where the misfit function is the sum of the squared differences between the wave numbers along the predicted and observed dispersion curves. This procedure, denoted as wave-equation dispersion inversion of guided Pwaves (WDG), is valid for near-surface waveguides with irregular layers. The importance of this work is that the WDG tomograms have higher resolution than the traveltime tomograms (WT) and mitigates the local minima problem of full waveform inversion (FWI). Numerical simulations and field data examples suggest that WDG is effective for selected 2-D P-velocity models where the dispersion curves can be readily identified.