3D Inversion of Magnetotelluric Data from the Sipoholon Geothermal Field, Sumatra, Indonesia

Abstract

The Sipoholon geothermal system in Sumatra has been identified as a moderate temperature geothermal system based on geothermometry. This geothermal field is characterised by 18 hot springs and located around the Tarutung basin, a pull-apart basin in the Sumatra fault. Debates continue on how this geothermal system works. 3D inversion of magnetotelluric (MT) data has been performed using the ModEM code. Six different schemes (using different components, rotation, and error floor settings) were used to investigate the effect of each scheme on the model result. Although the inversion results of the six schemes exhibit different conductivity contrasts, all of them display similar structures. All models show a shallow conductive anomaly beneath the Tarutung basin and a vertically elongated conductor at the eastern part of the Tarutung basin. The shallow conductor beneath the Tarutung basin is interpreted as unconsolidated sediments of volcanic origin, e.g. the young Toba Tuff (74 ka). The vertical conductor coincides with the location of Panabungan hot spring and normal fault zones. This vertical conductive zone indicates a circulating hot fluid heated up by deep magmatic activity due to the subduction process.