Tectonic Control to Geothermal System of Way Panas, Lampung, Indonesia

Abstract

Way Panas is part of Ulubelu geothermal field, which is situated at the southern end of Sumatra Island, Indonesia. This geothermal field is built along the active Sumatran Fault Zone, which also had acted as the main control on the development of geothermal system on the area. Abundant surface thermal manifestation were observed in the Way Panas, such as hot springs, fumaroles, gas discharges, mud pots, steaming grounds, and altered rocks. Several geologic and geophysic studies have been conducted, and some geothermal system model were proposed. However, since this area were strongly controlled by tectonic processes, it is noticed that the role of geologic structures have never been put in considerable study. This paper presents recent findings on tectonic and structural geology based on geologic mapping and remote sensing interpretation. A number of 1938 lineaments were extracted from digital elevation model, which were analyzed according to their respective rock ages. A number of 220 tectonic joints and fault kinematic were analyzed from field data. It is observed that those surface manifestations were associated with major NW-SE normal fault, which acting as boundary fault of Early Pliocene structural graben that filled by Plio-Pleistocene volcanic complex. This NW-SE structural trend was part of the Sumatran Fault system, and its reactivation produced extensional faults and joints controlled the outflow of geothermal system. Another significance finding was arcuate geologic structures produced by volcanic load that influenced the existing geothermal system.