Geophysical prospecting related to earthflow reactivation and hazard assessment: a study based on Huangnibazi slope failure in Sichuan Province, China

Combined geophysical surveys were performed to evaluate the stability of Huangnibazi earth-flow located in Sichuan Province, China. The mass of debris landslide was extremely non-uniform and preferential outflow tracks were established in it. Hence, the identification of the subsurface water seepage channels and their spatial distribution is the main concern. The landslide hydro-geological characteristics and structures are the essential source to evaluate the landslide stability, protection, and administration. The investigation was performed few months after the landside occurrence and a geophysical survey was designed to identify the vulnerable sections. The geomorphological features indicate that the topsoil of the accumulated debris is highly unconsolidated and the debris is a potential threat for the community in case of reactivation. From the geophysical results, we interpret and identify susceptible geological boundaries that are highly saturated and can act as the source for reactivation. From the lateral and spatial distribution of active and inactive materials, we concluded that the landside reactivation can initiate anywhere between the depth of 30–50 m. An analysis was performed by creating a 3D model from the electrical resistivity method to illustrate the stable and unstable debris sections. Slope stability models were established by comparing surface waves and electrical resistivity data of Huangnibazi stable and disturbed sections. The comparison shows that it is a good practice in detecting landslide hazards and locating extents that do not originally give the impression of failure conditions but are actually at high risk.