Determination of near-surface shear-velocity structure based on the joint inversion of Rayleigh-wave dispersion and ellipticity from multistation active-seismic records

摘要

The dispersive characteristics of high-frequency (>= 2 Hz) Rayleigh waves have been widely applied to determine subsurface shear velocity (V-S). However, the V-S of the high-velocity surface layers (e.g., rigid roads in urban areas) and underlying layers is poorly constrained in the Rayleigh-wave dispersion inversion. Compared to the phase velocity, the Rayleigh-wave horizontal-to-vertical (H/V) ratios of particle motion (i.e., ellipticity) are particularly sensitive to shallow V-S structures. Therefore, we have proposed a robust method for obtaining near-surface V-S structures by inverting Rayleigh-wave dispersion and H/V data. Initially, we separate the fundamental-mode Rayleigh waves from the active-seismic records using a high-resolution linear Radon transformation method. Then, we extract the high-frequency H/V and interstation phase travel-times from the separated fundamental mode using deconvolution interferometry and the frequency-time analysis method. Based on the phase travel-times, we calculate the phase velocity dispersion using ray-based tomography. Finally, we perform the joint inversion of dispersion and H/V data to obtain the V-S structure. According to the inversion results of synthetic and field data, the accuracy of the V-S in the rigid surface layer and underlying layers is considerably improved. We find that the joint inversion of Rayleigh-wave phase velocity dispersion and H/V data from surface-wave surveys is a useful tool for accurately determining the complex shallow V-S structures.