Joint wave-equation inversion of Rayleigh- and Love- dispersion curves

Wave equation dispersion (WD) inversion techniques for surface waves have proven to be a robust way to invert for the shear-wave (S-wave) velocity model. Unlike 1D dispersion curve inversion, the proposed WD method obviates the need for a layered model assumption and reduces the susceptibility to cycle-skipping issues in surface wave full waveform inversion (FWI). Previous WD inversion experiments conducted on Rayleigh and Love waves have highlighted that inverting Love waves yields better stability due to their independence from the P-wave velocity model. Nevertheless, Rayleigh waves possess the advantage of greater penetration depth compared to Love waves with similar wavelengths. Therefore, combining the two types of surface waves is a feasible way to improve the accuracy of S-velocity tomograms. In light of this, we propose a novel approach: a joint WD inversion encompassing both Rayleigh and Love waves. This innovative technique adjusts the weighting of individual WD gradients using the sensitivity factor of an equivalent layered model, offering a significant advancement in subsurface characterization. Synthetic model tests demonstrate that the joint WD inversion method can generate a more accurate S-velocity model, particularly in the presence of complex low-velocity layers (LVL) or high-velocity layers (HVL), when compared to individual wave WD inversion techniques. Simultaneously, the results of field tests validate the effectiveness of the proposed joint WD inversion strategy in producing a more dependable S-wave velocity distribution that aligns closely with the actual geological structure.