Identification of Non-Volcanic Geothermal Systems Based on Gravity, Magnetic and Land Surface Temperature Satellite Data in the Sajau Hot Springs Area, North Kalimantan Nanda Ridki Permana (a*), Fadhlur Rahman (b), Belista Gunawan (b), Ayu Alvita Primastika (b), Dhika Faiz Fadrian (c), Fardhan Rafshan Zani (c), Amara Wulandari (c), Melly (c)
a) PT Minelog Services Indonesia, Bumi Serpong Damai (BSD), Industrial Estate and Warehouse Techno Park Block G1 Number 10, Sektor 11 Street, Setu, South Tangerang, Banten, 15220, Indonesia.
*nandaridki836[at]gmail.com
b) GeoXplore Indonesia, Kincir Air Street, Pondok Manggis Block B6, Bojong Baru, Bojonggede, Bogor, West Java, 16920, Indonesia.
c) Departement of Physics, Faculty of Science and Technology, Syarif Hidayatullah State Islamic University Jakarta, 95 Ir. H. Juanda Street, Cempaka Putih, Ciputat, South Tangerang, Banten, Indonesia, 15412, Indonesia.
Abstract
Geothermal is an alternative energy source that needs to be developed along with the increasing population in Indonesia. Given that Indonesia has the second largest geothermal potential in the world with reserves of 29 GW. One of the non-volcanic geothermal areas is in Sajau Village, North Kalimantan with manifestations in the form of hot springs. To find out the geothermal system in the area, a subsurface investigation is needed involving the correlation between gravity, magnetic and Land Surface Temperature (LST) methods. Gravity and magnetic data are satellite data with each data obtained a total of 8536 and 2610 data. The data is then processed to provide a very good correlation between the gravity and magnetic anomalies around the Sajau hot springs. It can be seen that the position of the high gravity anomaly (0.1 \(-\) 0.6 mGal) is the same as the low magnetic anomaly (-1.095 \(-\) (-0.444) nT), where the high gravity value is caused by rock intrusion below the surface and the rock intrusion causes the rocks around it to be altered so that the value magnetic field decreases in the surrounding rock. The results from the LST show surface temperatures around the Sajau hot springs with values ranging from 25.7 \(-\) 28.3 degree Celcius which are caused by the temperature of the hot steam and the presence of heat source (intrusive rock) and rock alteration due to hydrothermal flow. In 3D inversion modelling, two model sections trending west-east were carried out, where sections A1 - A2 and B1 - B2 show each other sandstone as a reservoir with a density of 2.565 \(-\) 2.67 gr/cc and a depth of 500 \(-\) 1400 m. The geothermal system in the Sajau area was formed due to a fault which causes rocks to rub together so that the subsurface temperature rises and heats groundwater by convection around the fault.
