Investigation of deep-seated heat source through 3-D Magnetotelluric inversion in Arjuno-Welirang volcanic complex (East Java)

Abstract

Arjuno-Welirang is a volcanic complex with quaternary ages in East Java Province, Indonesia. Various geothermal systems in the area might exist, from inactive to still-active hydrothermal systems and even volcanic (magmatic) hydrothermal systems. To differentiate the status of geothermal systems to be useful for further exploration programs, it is necessary to investigate the deep-seated heat source responsible for supporting heat to the existing geothermal systems. To achieve the objective, Magnetotelluric (MT) is used to image the subsurface resistivity variation down to about 20 km. A total of 117 MT stations have been included to fill the coverage area, especially in the eastern and southern regions of the research area. A series of data processing has been conducted to improve the quality of MT data, and 3-D inverse modeling has been applied after processing. In addition, the exploration is also focused on identifying the extension of the high-temperature reservoir with benign fluid. Based on the 3-D inversion of MT data, the updome of resistivity structure at the deeper level below Mt. Welirang is identified as a deep-seated heat source indication supporting the main upflow reservoir zone. A possible reservoir extension to the western side of Mt. Welirang–Mt. Kembar complex is more prominent as indicated by the resistivity pattern, supported by the Cangar and Coban hot springs occurrence as an indication of an outflow zone. This extension zone could be one of the focused areas for further exploration drilling to avoid magmatic fluid that probably exists at the main upflow zone.