Numerical comparison of Rayleigh and Love full waveform inversion in characterizing soil spatial variability for near‐surface engineering applications

Abstract

The use of surface wave testing for near‐surface engineering applications has increased in recent years. Typical surface wave analysis is based on the dispersion of surface waves in one‐dimensional layered models. One‐dimensional models are inappropriate for measurements at sites with appreciable lateral variability, a likely scenario in many engineering applications. Use of such models can subsequently undermine the reliability and accuracy of the surface wave results. Full waveform inversion (FWI) is a high‐resolution imaging technique that is proven to outperform the conventional dispersion‐based analysis of surface waves. Much of the near‐surface literature has focused on full waveform inversion of Rayleigh waves developed by the interaction of primary‐ and vertically polarized shear waves (P‐SV), and the capabilities of surface waves generated by horizontally polarized shear waves (Love waves) in mapping near‐surface spatial variabilities have not been fully explored. In this numerical study, full waveform inversion of Rayleigh and Love waves was performed on two different spatially correlated Gaussian random fields (mean VS of 200 and 500 m/s) to mimic the natural spatial variability of geologic materials. Each soil structure was produced at a low and high level of stiffness variability. Two sources with different frequency contents, 25 and 50 Hz, were used to evaluate the effects of source characteristics on the resolution of Rayleigh and Love waveform inversions. The inverted results from the high‐velocity domain demonstrated that Love waveform inversion using high‐frequency seismic sources outperforms Rayleigh full waveform inversion in detecting the shape and the velocities of horizontally deposited geologic materials. Results from the low‐velocity domain also confirmed that Love full waveform inversion was comparable or superior to Rayleigh full waveform inversion, though the performance difference was less significant. However, the 25‐Hz frequency inversions yielded superior results than the 50‐Hz frequency inversions for the low‐velocity domain because the dominant wavelength of the high‐frequency signals becomes so small that it offers an impractically small investigation depth.