Characterization of an active landslide structure with integrated electrical resistivity tomography and multi-channel analysis of surface waves methods in Degirmendere district, Sakarya (Turkiye)

Abstract

Landslides following the development of slope instability can have serious consequences. Geophysical surveys have potential to aid in the understanding of landslides and their instability. This study described a landslide that occurred under particular geomorphological and meteorological conditions in Erenler (Sakarya, NW Turkiye) using electrical resistivity tomography (ERT) and multi-channel analysis of surface waves (MASW) surveys and mechanical drillings. Data showed that the landslide is characterized by downslope movement of an altered clay unit over a claystone unit. The traditional landslide model used to interpret geoelectric data involves sliding of a relatively low-resistivity material over higher resistivity bedrock. Here, the ERT survey showed a relatively high-resistivity sliding material moving over relatively low-resistivity bedrock units corresponding to the claystone unit. The relatively lower resistivity of the whole study area was related to the clay-rich materials detected in the boreholes. This low-resistivity unit was detected at high velocity in the MASW section, and it was understood that this layer was a compact structure acting like bedrock. The detected slip surfaces, landslide scars and slip surface toe indicate that the movement character of the landslide is retrogressive. The study results showed that the integrated and comparative use of different geophysical methods effectively reduces interpretation uncertainties and potential errors and leads to much better landslide characterization. A rarely encountered landslide substructure was clarified in the study carried out in the landslide area in the Erenler/Sakarya district. The landslide structure was characterized as a retrogressive model using integrated ERT and MASW geophysical and geological methods.image