Progress and prospect of surface-wave imaging techniques in near-surface applications

Elastic properties of near-surface materials and their effects on seismic wave propagation are of fundamental interest in groundwater, engineering, and environmental studies. Shear-wave velocity is used to determine 'stiffness', one of the key properties in construction engineering. Since, shear wave velocity is a function of depth, it can be derived from inverting the phase-velocity dispersion curve of the surface wave. The dispersion curves of surface waves can be extract from both the active source stimulated seismograms and the seismic ambient noise data. Surface-wave imaging technologies based on active and passive sources have been developed rapidly in recent years. They are widely applied in global and regional Earth's interior imaging, energy resources exploration, near-surface geological survey, non-destructive testing and environmental survey. Surface waves are interesting because they can be used to develop noninvasive techniques for characterizing a medium at small, large, and intermediate scales. Thanks to the lively scientific debate among different disciplines, the surface-wave imaging method is under continuous and rapid evolution, and interest in the technique has increased significantly during the last decade. By literature investigating, it can be concluded that research on surface-wave methods including, but not limited to the following aspects: forward calculating techniques of surface-wave dispersion curves, numerical simulating of propagation of surface waves, surface-wave properties in medium with complex structures, dispersion energy curves extracting techniques from multichannel surface-wave data, inversion algorithm of surface-wave dispersion curves, properties of multi-mode surface waves, properties of multi-component surface waves, properties of surface waves in layered medium with hard or soft layer, techniques of extracting high-resolution dispersion curves from seismic ambient noise data, full-waveform inversion of surface-wave data, application of higher-modes surface wave data, surface-wave data acquisition techniques, and so on. As a reviewing article, we briefly introduce the research history of surface-wave imaging methods based on Rayleigh and Love waves. The research and application status of higher-mode surface wave, surface-wave waveform inversion, ambient noise-based surface-wave imaging method and multi-component surface-wave imaging are discussed in detail. We also introduce some new technology in surface-wave data acquisition and processing, such as the distributed acoustic sensing and the high-speed-train seismology. Finally, we give an outlook for future development of surface-wave imaging technology.