Geoelectrical Prediction for Sliding Plane Layers of Rotational Landslide at the Volcanic Transitional Landscapes in Indonesia

The transitional between Quaternary and Tertiary volcanic landscapes is characterized by very deep interlayered clays. The the study of clay occurrence at certain depth through geophysical application is not intensively studied yet. Our sampling site is located at Bompon Sub-watershed where the rotational landslide are freqwently occurred. This research aims to investigate the characteristics of clay layer that potentially become sliding surface of landslides using two-dimensional (2D) resistivity method. Resistivity survey using dipole-dipole configration was conducted above three types of rotational slides typically occurred in the study area. We also did field observation as well as laboratory measurement for supporting data interpretation. Three kinds of interlayered clay materials are clearly detectable from 2D resistivity sections under all bodies of landslides. Those materials are entirely categorized as clay but different on cracks structure and cracks density, soil moisture, total porosity, bulk density, and specific gravity. Based on its physical characteristics, the saturated clay located around 10 up to 20 meters in depth is the most likely becoming sliding surface of landslides. This result is useful for understanding the nature of rotational slides commonly occurred in the volcanic transitional landscapes in Indonesia.