Geometrical Pattern Estimation and Resistivity Cross Section Imaging of The Lembang Fault Using Electrical Resistivity and TEM (Transient Electromagnetic) Methods

As the previous study known, based on surfacelevel observational analysis using GPS data from Light Detection and Ranging (LiDAR) satellite imagery with a resolution of 0.9 m and Interferometric Synthetic Aperture Radar (IFSAR), it is presumed that The Lembang Fault is an active sinistral strike-slip fault located approximately 10 km north of Bandung, extends for about 29 km and is divided into six segments. Previous palaeoseismological studies indicate a slip rate of 3-5.5 mm/ year, with the potential to generate earthquakes of magnitude 6.5-7 on the Richter Scale. This highlights the importance of detailed investigations to support disaster mitigation strategies. One approach involves examining subsurface geometric patterns and resistivity distributions using Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES), and Transient Electromagnetic (TEM) methods. Four sites suspected of active tectonic deformation were analyzed: Batu Lonceng (Line 1), Gunung Batu (Line 2), Jambudipa (Line 3), and Cimeta (Line 4). Refers to Geological map and the Resistivity table by Telford, at Batu Lonceng, an SW-NE ERT profile revealed a SE-NW thrust fault caused by volcanic uplift (2.195-13.611 ohm.m-1 at 32.5 m depth). At Gunung Batu, VES data indicated volcanic uplift with high resistivity values (857-5.143 ohm. m-1) and SE-NW thrust fault at 15 m depth, while TEM analysis suggested an anticline of alluvial and sandy deposits, with resistivity values of 300-700 ohm.m-1 at 50m depth. In Jambudipa, interpolation of an ERT West-East profile and TEM data along the North-South direction revealed a SE-NW thrust fault in Muril Hamlet at 40 m depth (300-400 ohm.m-1) within volcanic lithology. Finally, at Cimeta, a North-South cross-section identified a NW-SE trending normal fault at 10 m depth (54-113 ohm.m-1) composed by volcanic sandstones and limestones. Overall, inversion results across all sites achieved RMS errors below 5%, demonstrating consistency with geological mapping and confirming the reliability of the integrated ERT, VES, and TEM approaches in characterizing active tectonic structures along the Lembang Fault.