Geothermal play fairway analysis at a populated rifting basin area of Taiwan

Abstract Taiwan is located in the active mountain belts on the west side of the Pacific Rim with promising potentials for geothermal resources. The triangular shaped Yilan Plain, our study area chosen for a geothermal development pilot project, resides at the southwestern end of the Okinawa Trough behind the Ryukyu Arc-Trench where the Philippine Sea Plate is subducting beneath the Eurasian Plate with low-grade metamorphic rocks exposed in the surrounding mountain ranges. Play Fairway Analysis (PFA) is adapted to demonstrate important aspects, predicting geothermal potential through quantitative and statistical methods in a given type by overlapping each element layer into a composite favorability map with properly calculated weights accounting for uncertainty levels. Highlighted exploratory sweet spots on a regional scale can be identified with the easy-to-read map for decision-making stakeholders. Three components are selected for this analysis: they include (1) heat sources: with temperatures of hot springs, geothermal gradients, and silica geothermometry, (2) permeable fracture networks: with fault lines, drainage network, micro-earthquake activities, and dilation rate distribution, and (3) human activities: with population density, sediment thickness, and hazardous risk. Expert opinion on factor weighting for two geological components and Analytic Hierarchy Process (AHP) for the socioeconomic component are utilized to determine weightings representing the assigned confidence and uncertainty levels. ArcGIS software is used as the platform for data processing and map demonstration. The final map displayed the combined geothermal favorability from the two geological aspects blocked out with the riskier zones from the socioeconomic aspect. It indicates two potential prospects with one in the southwestern hillside where the Chingshui power plant resided and another in the southeastern portion of the Yilan Plain, which could interfere with certain human activities.