Characterizing the 3D hydrogeological structure of a debris landslide using the transient electromagnetic method

Abstract

Debris landslides are one of the most common types of landslides in the Wenchuan earthquake area. The characteristics of the hydrogeological structure are the basis for landslide stability evaluation and protection treatment. The preferred seepage paths developed in debris landslides control the flow of groundwater and have a direct impact on the soil instability and sliding surface instability. Therefore, it is particularly important to understand the groundwater seepage system. Recently, many joint geophysical surveys have been used to detect the hydrogeological structure of landslides. However, these joint surveys aim to detect structures on a large scale and do not focus on the seepage path systems in debris landslides. It is difficult to detect the 3D structure of the seepage path system in detail, taking into account the portability, penetration, and resolution while meeting the practical needs of landslide prevention. To date, no one method has been identified as the best detection method for characterizing complex 3D hydrogeological structures. To reveal the complex seepage paths efficiently, we investigated a debris landslide in Xishan village, Sichuan Province, China, by using the transient electromagnetic method (TEM), which is a fast and portable method. Additionally, we proposed an effective quasi-3D inversion strategy with kdTree to determine the geoelectric structure and to make a geological interpretation. The interpretation was verified with field engineering surveys, other geophysical surveys, and remote sensing data. The results suggest that the complex 3D structure in this debris landslide is characterized by a dendritic pipe network-like seepage drainage system. In addition, this work assessed the ability to detect different parts of the landslide based on the given resolution. Furthermore, the resolution and detection efficiency of the TEM were compared with those of other geophysical methods. The assessment and comparison demonstrated that the TEM can be used as the main survey method to fulfill the real-world demands of detecting seepage path systems in a debris landslide.