Determination of the Landslide Slip Surface Using Electrical Resistivity Tomography (ERT) Technique

Indonesia is located among three interacting active tectonic plates, causing the country to become vulnerable to geological disasters; landslides being one of them. Deforestation and over-population on the hillsides have escalated the formation of critical areas where landslides and other geological disasters are an occurrence. It is therefore important to study the geometry and the depth of the slip surface of a critical area in order to recognize the indicator of landslides. In situ geophysical techniques enable the measurement of physical parameters, either directly or indirectly (via satellite), linked with the lithological, hydrological and geotechnical characteristics of the terrains related to landslides. The objective of this research is to determine slope stability analysis using a geophysical method described as Electrical Resistivity Tomography (ERT). Data from 1-D and 2-D Electrical Resistivity Tomography (ERT) analysis conducted in Cianjur, West Java's one of the most critical areas for landslides due to its steep hilly area showed that there was a contrast in the resistivity value. It showed different kind of layers in the soil, and the boundaries between these layers played a role as a slip surface. The data also showed that there were two slip surfaces in the research area: at the bottom and the top of the slopes. These provided the margins between the higher resistivity value of the upper layer and the lower resistivity value of the lower layer. The upper layer was concluded as clay soil and the lower one as more sandy soil. Determining slip surface using ERT helps to analyze the stability of the slope.