Integrated satellite gravity analysis and HVSR microtremor measures for geothermal potential assessment in the Suban Curup–Rejang Lebong Hot Spring Area, Indonesia

A geothermal potential assessment was conducted in the Suban Curup–Rejang Lebong Hot Spring Area, Bengkulu Province, Indonesia. This study aimed to identify subsurface geological structures—faults, volcanic features, and sedimentary layering—that may control the development of geothermal reservoirs and caprock units. Two complementary geophysical approaches were integrated: (1) Three-dimensional (3-D) inversion modeling of Bouguer gravity anomalies derived from Global Gravity Model plus (GGMplus) 2013 and corrected using SRTM2gravity at 1,937 measurement points, and (2) microtremor acquisition at 106 sites with 60-minute recording duration, processed using the Horizontal-to-Vertical Spectral Ratio (HVSR) method. The residual gravity inversion results reveal density contrasts of 2.40–3.40 g/cm³ and sediment thicknesses exceeding 80 m, interpreted as potential geothermal reservoir units. These findings are consistent with the HVSR results, which show moderate to high amplification (A₀ = 3–9) and natural frequencies of 1–10 Hz, indicating porous and fractured formations favorable for fluid storage. Overall, the integration of satellite gravity and microtremor data highlights the presence of thick sedimentary deposits and structurally controlled pathways, suggestive of promising geothermal reservoir targets in the Suban Curup area.