digilib@itb.ac.id +62 812 2508 8800

Indonesia has a large potential of geothermal resources, however it has not been fully harvested yet, therefore it is necessary to research areas with geothermal resources. One of which is the Pariangan geothermal area in Tanah Datar Regency, West Sumatra Province which is the object of this research. To identify the geological structure and subsurface model of the Pariangan geothermal area, topography and gravity data from a research by PSDG in 2014 as well as other supporting data such as geological, geochemical, and geophysical data were used. In this study, complete Bouguer anomaly was calculated which was then made into a complete Bouguer anomaly map, then regional and residual anomaly maps were made using a window size 7 moving average and 3rd polynomial order trend surface analysis filter. The location and depth of the Pariangan geological structures were estimated using the Euler deconvolution method. Based on the residual anomaly map, an anomaly pattern with a northwest–southeast trend can be identified which represents faults. Based on the Euler deconvolution solution, faults which are predominant at a depth of <900 m can be identified. The Pariangan subsurface model consists of andesite, serpentine insert in a fault, and slate as the bedrock. The Pariangan geothermal system conceptual model consists of a heat source from the volcanic activity of Mount Marapi, a reservoir that is estimated to be old andesite, a caprock that is estimated to be young andesite that underwent argillic alteration, a recharge area around the peak of Mount Marapi, and a discharge area at the foot of Mount Marapi in the form of Pariangan Hot Spring as a result of upflow and Sopan Didih Warm Spring as a result of outflow.