Way Ratai Deep Plutonic Body revealed from 3D Gravity modeling using Satellite Data and its Implications for the Way Ratai Geothermal System

Abstract

The Way Ratai geothermal area in Pesawaran Regency, Lampung Province, is a geothermal prospect located along the Sumatra volcanic arc. This study aims to identify the presence of a deep plutonic body as a potential heat source and to assess its implications for the local geothermal system. Gravity data were obtained from satellite observations via GGMPlus, followed by terrain and Bouguer corrections, and regional–residual anomaly separation using a Gaussian filter. The residual anomalies were used as input for 3D density inversion modeling with Grablox, Bloxer, and the Conjugate Gradient method, enabling the mapping of subsurface density distribution down to a depth of 5 km. The modeling results reveal a vertically oriented low-density zone (1.70 - 2.44 g/cm³) associated with altered and fractured rocks, interpreted as a plutonic body acting as a conduit for geothermal fluid migration. This zone is surrounded by higher-density rocks (2.50 - 2.80 g/cm³) that function as structural boundaries and fluid traps, while major faults are inferred to enhance permeability and system connectivity. These findings support the concept that deep plutonic intrusions, combined with geological structure control, play a crucial role in the formation and sustainability of the Way Ratai geothermal reservoir, providing valuable insights for exploration and field development planning.