Geological structure identification in Tulehu geothermal prospect area using gravity data analysis

Tulehu is one of geothermal prospect areas located in east Indonesia, which is in Maluku Province. The geological condition of the area is dominated by quaternary volcanic rocks like lava flow, lava dome, and pyroclastic flow, which probably associated with Mt. Eriwakang and Mt. Huwe. But the area is mostly covered by limestone, especially in the southern part of the area. The geothermal prospect of Tulehu is indicated by the occurrence of hot springs spotted along Banda Fault, Banda-Hatuasa Fault, and Huwe Fault in the southern part of Tulehu. In order to understand the subsurface geological structure and its correlation to Tulehu geothermal system, gravity survey was conducted. Gravity survey was carried out using Scintrex CG-5 gravimeter with total of 130 stations were measured with 500 m spacing. The result of CBA and residual gravity indicated the existence of low gravity anomaly at the Mount Eriwakang, while the high gravity anomaly found around several structures obtained from Remote Sensing. Several structures were detected by FHD method, those are Huwe Fault, Banda Fault, Tulehu Fault, and Wayari Fault. Based on SVD method, the type of faults are identified. These structures also supported through 2-D gravity forward modeling. The 2-D gravity modeling results several layers that build the geothermal system of Tulehu, those are Limestone with density of 1.79 g/cc, Pyroclastic with density of 2.67 g/cc, Andesitic Lava with density of 2.6 g/cc, claycap with density of 2.2 g/cc, and Basement with density of 2.81 g/cc.