Electrical resistivity tomography for geohazard assessment in West Lombok’s alluvial plain

Abstract

Electrical resistivity tomography (ERT) is widely used for mapping subsurface conditions and is very useful for assessing geohazards. Variations in resistivity can suggest anomalies that can be linked to fault zones, or sediment layering that specifies a particular body, such as sediment-filled basins, or loose soils that are prone to earthquake amplification, liquefaction, and ground failure. This study examines two alluvial plains in West Lombok: Mataram city (the densely populated capital) and Tanjung (a coastal tourist area). Alluvial plains are especially vulnerable to geohazards because their loose, water-saturated sediments intensify seismic shaking and raise liquefaction risks during earthquakes. Our ERT models show a consistent subsurface structure: sand-dominated layers extending beyond 30 meters, topped by pumice-rich volcanic deposits. In some areas, shallow groundwater (<2 meters deep) was detected, further increasing liquefaction potential. Specific resistivity patterns match known liquefaction features, which suggest historical liquefaction had occurred in Mataram. These results emphasize the importance of combining ERT with direct methods, such as trenching and boreholes, to verify subsurface models and refine hazard assessments.