Interpretation of Gravity and Magnetic Data to Delineate Local Fault Structures in Bur Ni Geureudong Geothermal Field, Aceh Province, Indonesia

Abstract

Fault structures play an important role in a geothermal system. Therefore fault mapping needs to be done in a geothermal field prior to further development. For this purpose, we have used gravity and magnetic methods to map subsurface fault structures in Bur Ni Geureudong geothermal field at District of Bener Meriah, Aceh Province, Indonesia. Gravity data were measured at 24 stations along 27 km, crossing the area in the NE-SW direction. To obtain complete Bouguer anomalies of the gravity data, measured data has been done drift, latitude, free air, Bouguer, and terrain corrections. The total magnetic field anomalies were obtained by applying diurnal and International Geomagnetic Reference Field (IGRF) corrections. The total magnetic field and the complete Bouguer anomalies were used for 2D forward modeling by applying Mag2DC and Grav2DC codes, respectively. These codes are based on 2D model of Talwani polygon. Both models show that the research area subsurface consist of three layers, mainly volcanic breccia superimposed by tuff and pyroclastic layers at the top and limestone estimated to be at the bottom layer. With regard to geothermal manifestations, the expected models also show four parallel normal faults directed in northwest – southeast, located in Wihni Durin, Tapak Muge, Wonosobo, and Bale Atu. The existence of fault line in Wonosobo is in agreement with location of Uning Bertih geothermal manifestation.