Geoelectric Analysis for Potential Slip Plane Interpretation in Labuan Bulan Hill, Salem District, Brebes Regency, Central Java

Abstract

Landslide is a natural disaster which often occurs in Indonesia. Based on National Disaster Management Agency (BNPB), there were 1,321 landslide incidents which occurred in 2021. Labuan Bulan Hill located on high susceptibility landslide seen from Landslide Susceptibility Zone of Brebes Regency, furthermore, soil tensile cracks presence with 5 - 50 cm width and 15 - 125 cm height at upper slope. In this study, the identification of subsurface lithologies and potential slip plane was carried out using geoelectric survey method with Wenner – Schlumberger configuration. The Wenner – Schlumberger configuration has deeper penetration than other geoelectric survey configurations. Geoelectric surveys are carried out on two lines with 240 m length and 5 m electrode space. Geoelectric line is made parallel and perpendicular with slope direction to estimate subsurface conditions easier with the help of tensile cracks presence in the surface. Results of measurements identified that the upper layer consists of poorly graded silty sand with 285 Ωm – 1700 Ωm resistivity, the second layer is a moderate - highly weathered volcanic breccia with 129 Ωm – 285 Ωm resistivity, and the third layer is fresh – slightly weathered volcanic breccia with 285 Ωm – 1388 Ωm resistivity. A fresh – slightly weathered volcanic breccia layer was identified as potential slip plane with 20 – 30 m depth.