Resistivity model of hallow subsurface to find the path of geothermal manifestation in Bora Village of Sigi Regency of Central Sulawesi

Abstract

Bora geothermal is one of the manifestations that appear at the meeting of two fault zones namely Palu-Koro Fault and Palolo Fault. This geothermal is classified as non-volcanic. Existing tectonic activity, presumably leading to the formation of a depressive zone that triggers a rock intrusion process that conducts heat conductively. To find out the sub-surface structure, we apply the electrical resistivity tomography (ERT) method. The data collection technique we use is 2-D imaging with Wenner configuration, where the number of electrodes is 21 pieces at 6 m intervals. Shallow depths Penetration targeted about 20 m below ground surface (m.bgs. The resistivity values obtained are in the range < 0.15 Ohm.m to > 56.6 Ohm.m which indicates the subsurface layer is strongly influenced by the fluid. However, the interesting thing here is that the hot water pool formed on the surface of about 6 m dimension is passed through the path of ERT measurement around the electrode number 11 and 12, illustrated in the resistivty section to ± 10 m.bgs depth and turning toward the electrode number 4 up to 7 as the lowest anomaly source at depth > 15 m.bgs. This configuration of low resistivity anomaly is what we interpret as a shallow ground pathway with local high temperatures as the source of the emergence of Bora geothermal manifestations.

Applying Deep Electrical-Resistivity Tomography Techniques for the Exploration of Medium- and Low-Geothermal Energy Resources

“…In the case of high-and medium-enthalpy geothermal systems, these present great variations in their resistivity/conductivity structure, usually associated with the occurrence of fluids but also with the presence of anomalous concentrations of hydrothermal minerals. The existence of particular fluids, such as saline fluids or meteoric water in rocks, results in enhanced electrical conductivity to a greater or lesser extent, depending on the characteristics of this fluid [33][34][35]. In these cases, ERT methods are an important source of information, but they also constitute a great help in those surveys where the initial thermal evidence is not so clear, but a possible state of fracturing or structural disposition could indicate the potentiality of geothermal exploitation at different scales.…”