Combined use of active and passive surface waves for the S-wave velocity structure delineation beneath the Balikun Basin, China

Rayleigh waves have been widely used to estimate the shear-wave velocity structure in the fields of shallow engineering and environmental detection. In this study, active and passive surface wave surveys were performed sequentially on the same survey line across the eastern Balikun Basin. MASW (Multi-channel Analysis of Surface waves) technology was utilized for active sources to obtain the phase velocity dispersion curves of the fundamental-mode Rayleigh waves. For the passive surface wave surveys, cross correlations were performed to retrieve the empirical Green's functions, from which the phase velocity dispersion curves can be measured by FTAN (Frequency-Time Analysis) method. We applied the 1D Surface wave tomography (SWT) to construct a phase velocity map which combines the two sets of dispersion curves obtained from active and passive Rayleigh waves. Finally, the obtained phase velocity dispersion curves were inverted for 1D shear velocity profiles and then 2D Vs profiles was constructed by assembling these 1D profiles. The results show that the investigation depth of active surface wave measurement is limited to several decameters, while the investigation depth of passive surface wave measurement can reach over a hundred meters, and combining these two methods can achieve a greater maximum depth of the Vs profile without sacrificing the near-surface resolution.