Vertical electrical sounding for revealing the groundwater resources in the geothermal spring of Jaboi volcano

Geothermal energy is considered renewable energy that is environmentally friendly and sustainable compared to the conventional energy from fossil fuels. However, uncontrolled geothermal exploitation can cause a decrease in the groundwater table and reservoir temperature, such as in the Jaboi volcano on Weh Island, where a power plant has been built to generate electrical energy with an estimated power of 50 MWe but still has not been operated. A geophysical survey is needed to determine the local hydrothermal system, including groundwater reserves under the surface which can be used to refill the hydrothermal wells during exploitation. This study measured vertical electrical sounding (VES) data at 15 points near the crater and geothermal power plant. In addition, very-low-frequency (VLF) data that pass through the crater were also collected to determine the presence of other hydrothermal resources such as fractures and faults. The results of the 1D least-square inversion show three subsurface models where groundwater resources with low resistivity (< 1.5 Ωm) are found at a depth of 50–100 m. The same results are also obtained from the 2D cross-section model that impermeable resistive anomalies in alluvial and tuff rocks dominate the near-surface area. The layer after groundwater is an impermeable rock in the form of breccia. The results of 2D VES and VLF modeling also show the presence of the Ceunohot and Leumomate faults, which are beneficial as fluid access to the surface. Based on the data analysis, the combination of VES and VLF data can be used to image shallow hydrothermal systems such as groundwater resources and faults in the Jaboi volcano.