Love-Wave Full Waveform Inversion in the Time Domain: Case Study of Ancient Tomb Prospecting

Surface waves contain abundant S-wave velocity information of subsurface media and are widely used for near-surface structural investigations. The multichannel analysis of surface waves method based on dispersion curve inversion is an effective tool for estimating S-wave velocity. However, its resolution and accuracy may be compromised when the underground medium exhibits strong horizontal inhomogeneity. Full waveform inversion (FWI) utilizes all the amplitude and phase information of surface waves to achieve higher imaging accuracy and resolution. Love waves, independent of P-wave velocity and more sensitive to S-wave velocity, make the framework of Love-wave FWI simpler yet more effective compared to Rayleigh waves. This paper develops a complete workflow of 2D Love-wave FWI in the time domain. The initial S-wave velocity model is established based on Love-wave dispersion information, followed by pre-processing of the observed data. The source wavelet is estimated using a source correction filtering technique. A pre-conditioned conjugate gradient algorithm updates the model, and a multi-scale strategy is employed to escape local minima. We applied the proposed Love-wave full waveform inversion method to real seismic data acquired in the suburbs of Xianyang City, China, with the aim of precisely locating an ancient tomb for subsequent archaeological excavation. The inverted S-wave velocity profile revealed a low-velocity anomaly buried at a depth of about 10 m, which highly matched the location and size of the actually excavated ancient tomb, confirming the effectiveness and practical value of this method in archaeological prospecting.