Imaging structural control of geothermal reservoir using remote sensing and gravity data analysis in Blawan-Ijen, East Java, Indonesia

Ijen Volcanic Complex is part of the Quartenary volcanic front of the Sunda Arc. The arc is a subduction system as a result of the northward subduction of the Indo-Australian plate underneath the Eurasian plate. This paper presents remote sensing data analysis and gravity data interpretation to understand the geological structure and its correlation to the geothermal system. The remote sensing analysis is performed using morphostructure approach. Furthermore, the gravity survey also had been carried out in the Ijen Volcanic Complex in 2017. A total of 72 gravity stations were measured with station spacing about 1-1.5 km. The gravity anomaly was then separated into regional and residual anomaly using the first order of TSA method. A high bouguer anomaly found in the southwest area and then continued to the northeast area. The high bouguer anomaly in the southwest area is might be associated with the existence of several volcanoes such as Mt. Mlaten, Mt. Lingker, Mt. Anyar, and Mt. Pendil. Futhermore, the low bouguer anomaly that is seen in the southeast area is probably caused by the collapse of the Mt. Kukusan. Moreover, a high residual gravity anomaly in the center of the caldera is coincided with the geological structure intersection of Kawahwurung fault, Blawan fault and Kendeng-Merapi fault.