Full-Wavefield Surface Wave Method: Integrating Rigorous and Efficient Methods for Enhanced Subsurface Exploration

Spectral analysis of surface waves (SASW) and multichannel analysis of surface waves (MASW) are the two main active surface wave methods, and their common inversion schemes are effective mode (EM) inversion and fundamental mode (FM) inversion, respectively. The former has a more rigorous inversion scheme, which considers receiver locations and dynamic response, while the latter has a more convenient dispersion analysis and fast inversion process. This paper introduces an improved dynamic response solution for elastic layered media subjected to vertical load. It is fast, accurate, and unconditionally stable, facilitating the full-wavefield inversion in terms of the frequency-velocity spectrum (FVS). The MASW FVS inversion merges the convenience and robustness of MASW dispersion analysis with the rigorous inversion scheme adopted by SASW. It is based on the actual dynamic response at receiver locations and takes into account possible higher modes and nonRayleigh waves. In this study, various types of synthetic velocity profiles are used to compare the inversion results among three different inverted schemes (SASW EM, MASW FM, and MASW FVS inversion). The results indicate that, when phase-unwrapping in SASW is not problematic, SASW EM inversion and MASW FVS inversion are theoretically sounder and produce better inverted results than the MASW FM inversion, while the process of MASW FVS inversion is more convenient and robust. Finally, a field example is used to further demonstrate the advantages of FVS inversion and its applicability.