Modeling the Subsurface Structure Beneath Mount Lawu, Karanganyar and Magetan Regencies Based on Magnetic and Gravity Data

Abstract Indonesia is one of the countries with the most potential geothermal resources in the world. One of the mountains that is a prospective area in Java is Mount Lawu, which has an estimated resource of 195 MW and a hypothetical resource of 137 MW. Unfortunately, the data in previous study have not been thoroughly processed. In addition, the modelling carried out was limited to each method. Therefore, this research aims to reconstruct magnetic and gravity observation data and model the subsurface structure related to the location of geothermal reservoirs on Mount Lawu. The magnetic and gravity data used were obtained from the Geophysical Integrated Survey Team report of Mount Lawu in 2009. Before modeling, the gravity data was corrected again. Forward modelling was then carried out using Oasis Montaj. In this study, the susceptibility value used has a range of 000034 - 0.049 cm 3 /g, while the density value has a range of 1.6 - 2.82 g/cm 3 . The modelling is done by making three sections with the error range of the magnetic method from 11.597 - 16.712 nT and the gravity method from 1.587 - 2.95 mGal. From the modelling done, it resulted in a subsurface structure that matches the geological conditions. Geothermal reservoirs have been identified in the area around Candradimuka Fumarole at a depth of 1500 m from the surface and the rock is Jobolarangan Lava 1. It is hoped that the results of this research will be taken into consideration in determining the location of exploration wells in the Mount Lawu area so that they can be exploited as soon as possible.