Characterization of the 2D shear wave velocity structure of the majiagou landslide in the three gorges reservoir area of China using seismic surface wave and borehole data

Abstract

Understanding the geological structure of the Majiagou landslide and accurately identifying the burial depth and geometry of potential sliding surfaces for evaluating the safety margin and failure risk of the landslide. The multi-channel analysis of surface wave (MASW) technique is widely recognized as the optimal method for determining near-surface shear wave velocity in geotechnical investigations. In this study, we used the MASW technique to characterize the geological structure of the Majiagou landslide. A total of 86 shot-gather records are collected, and a 2D shear wave velocity profile of the landslide is obtained through dispersion analysis and inversion processing. The reliability of the velocity structure and landslide stratification was validated using borehole data and monitoring results from the inclinometers and sensing optical fibers at corresponding survey locations. Shear wave velocity variations and borehole data indicate that the landslide is approximately divided into four layers within the upper 30 m, with a potential sliding surface identified. The middle section contains boulders and isolated stones of varying sizes, while the thicker sediment and gravel soil layers are predominantly concentrated in the middle and leading edges of the landslide, suggesting a higher likelihood of failure in these areas compared to the trailing edge. Finally, integrating the results of shear wave velocity with surface geological surveys, we infer that the most probable failure mechanism is a pushing-type landslide initiating at approximately 15 m depth from the middle of the landslide, proceeding towards the right side of the leading edge.