1-D Occam inversion of TDEM data for preliminary groundwater identification in post-earthquake Cianjur, West Java, Indonesia Marshanda Adisti Rahmadini (a), Ario Nawangsidi (a), Indriyati (a), Nurhasan (a), Enjang Jaenal Mustopa (a*)
(a) Earth Physics and Complex Systems Research Group, Physics Department, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jalan Ganesha No. 10, Bandung 40132, Indonesia
*enjang[at]itb.ac.id
Abstract
The 5.6 Mw earthquake that struck Cianjur Regency, West Java, Indonesia in November 2022 disrupted shallow groundwater systems across the affected area, exacerbating water scarcity during prolonged dry seasons. Located along the seismically active Cimandiri Fault, the region requires urgent subsurface characterization to support groundwater recovery planning. This study applied the Time-Domain Electromagnetic (TDEM) method to identify the preliminary subsurface resistivity structure for groundwater potential mapping in the affected area. TDEM transmits a transient pulse of electric current through a loop on the ground surface and records the decay of the induced secondary electromagnetic field over time, yielding depth-resolved resistivity profiles. Eight TDEM soundings were acquired and inverted using layered-earth models. The optimal model for each sounding was selected based on the lowest root-mean-square (RMS) misfit while maintaining geological plausibility. The resulting 1-D resistivity profiles were laterally stitched to construct pseudo-2D resistivity sections across the study area. Sounding locations were analyzed to identify low-resistivity anomalies interpreted as potential saturated zones based on the geological context of the study area. Inversion results reveal three distinct resistivity units: a shallow resistive layer (>100 Ohm.m) interpreted as dry volcanic overburden, an intermediate low-resistivity zone (5-20 Ohm.m) at depths of approximately 40-60 m identified as a saturated aquifer candidate, and a deeper resistive unit (>1000 Ohm.m) corresponding to compact basement rock. These findings provide a preliminary subsurface framework to guide further groundwater exploration and recovery planning in earthquake-affected Cianjur.
Keywords: TDEM, groundwater, Cianjur, 1D inversion
