Gravity Field Interpretation for Subsurface Structure Identification in a Tiris Geothermal Area, Indonesia

Indonesia hosts 331 geothermal prospects with a combined potential of 28,617 MW, yet by the end of 2024, only 13.2% had been developed, highlighting a critical need for improved exploration workflows. In this study, we characterize the subsurface geothermal architecture of the Tiris District (Probolinggo Regency, Lamongan–Argopuro volcanic complex) by integrating dense Bouguer gravity surveying (150 km²) with first horizontal and second vertical derivative analyses and three-dimensional density inversion. Bouguer anomalies range from 39.95 to 80.03 mGal, with highs in the eastern and western sectors and lows in the northwest and south, while derivative maps reveal a network of predominantly NW–SE normal faults that likely channel geothermal fluids. The inversion model uncovers a shallow low-density zone (1.0–1.5 g/cm³) to 0.75-km depth interpreted as fluid conduits, a sandstone reservoir layer (1.5–2.0 g/cm³) at 2–3 km, caprock units (2.0–3.0 g/cm³) at 0.5–2.0 and 3.0–4.0 km, and deep high-density bodies (3.3–4.0 g/cm³) below 4 km corresponding to magmatic heat sources. These findings refine the conceptual model for Tiris, demonstrate the effectiveness of integrated gravity derivatives and inversion in volcanic geothermal exploration, and underscore the region′s promise for sustainable energy development. By precisely delineating subsurface structures with precision, this work provides critical insights to guide sustainable resource development and targeted drilling strategies in volcanic geothermal systems.