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

•A deep-seated heat source is investigated to observe overall geothermal systems (inactive, still active, and magmatic systems) that possibly exist in the arjuno-welirang volcanic complex.•An MT survey with a broad range of frequency (320–0.001 Hz) has been carried out to investigate the deep-seated geothermal heat source as well as the possible high-temperature reservoir extension of neutral fluid in the arjuno-welirang volcanic complex.•The arjuno-welirang geothermal conceptual model shows the main upflow beneath the Mt. Welirang and the outflow toward Padusan, Cangar, and coban bicarbonate-type hot springs.•The most important finding indicates a thermal evolution from Mt. Arjuno, Mt. Kembar, to Mt. Welirang (inactive, still active, to magmatic systems), characterized by thickening and thinning patterns of conductive layers beneath this volcanic complex.•A possible extension captured from the MT model is seen toward the northwestern, western, and southwestern sides of Mt. Welirang–Mt. Kembar volcanic complex. 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