Magnetotellurics (MT) is an important geophysical method for exploring geothermal systems, with the Earth resistivity obtained from the MT method proving to be useful for the hydrothermal imaging changes of the system. In this research, we applied the MT method to map the geothermal system of the Seulawah Agam volcano in northern Sumatra, a site intended for the construction of a geothermal power plant with an estimated energy of 230 Mwe. Herein, 3D MT measurements were carried out, covering the entire area of the volcano and the various intersecting local faults from the Seulimeum segment in the NW–SE direction. Based on Occam 2D inversion, a conductive anomaly (<10 ohm·m) near the surface was identified in response to specific manifestation areas, including the Heutsz crater on the northern side and the Cempaga crater on the southern side. A further conductive anomaly was also found at a depth of 1 km, which was presumably due to a clay cap layer covering the fluid in the reservoir layer below the surface, where the manifestation areas are formed at various locations (where faults and fractures are found) owing to the fluid in the reservoir rising to the surface. The MT modeling also revealed that the reservoir layer in Seulawah Agam lies at a depth of 2 km with a higher resistivity of 40–150 ohm·m, which is the main target of geothermal energy exploration. At the same time, the heat source zone where magma is located was estimated to lie in two locations, namely, on the northern side centering on the Heutsz crater area and the southern side in the Cempaga crater area. A clear 3D structure obtained via Occam inversion was also used to visualize the hydrothermal flow in the Seulawah Agam volcano that originates from two heat source zones, where one structure that was consistent across all models is the conductive zone that reaches a depth of 5 km in the south in response to the regional faulting of the Seulimeum segment. Based on the MT research, we concluded that the volcano has the geothermal potential to be tapped into power plant energy in the future.

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Gravity Satellite has been widely used in tectonic studies and regional of geological mapping. The Satellite Gravity data are provided free by Scripps Institution of Oceanography, University of California San Diego. The data are acquired by GEOSAT and ERS-1 satellites with a 1.5 km resolution for one pixel. For a further application, the tilt derivative analytic technique was used in order to enhance linear trends of the geological structure revealed by the Bouguer anomalies. The method is represented by the value of an angle between the total horizontal and vertical derivative from the gravity data. The results show that the tilt derivative calculation has been able to map clearly some geological structures on the north of Sumatra i.e., the Aceh and the Seulimeuem segments, as well as some local faults around them. On the other hand, Banda Aceh as the capital city of Aceh Province and Pidie District is dominated by positive values of the tilt derivative anomalies. The data coincide with geological maps of both areas where they are covered by alluvial deposits. Based on the result, it can be concluded that the tilt derivative method is potentially used for quick interpretation of the satellite gravity data.

Seulawah Agam, a stratovolcano located in the Aceh province, Indonesia, has not erupted for a long decade after the last eruption in 1839. Thermal infrared remote sensing has been used to determine the land surface temperature (LST) of the volcano area. However, the application of remotely sensed thermal imagery in identifying the LST of the Seulawah Agam volcano, as a precursor of geothermal energy and eruption hazard, has not been completely monitored. The volcano locates relatively close to residential areas, which is a challenging approach to apply thermal bands in determining geothermal identities. In this research, we assess the LST and vegetation index for the detection of the thermal activity of the mountain. These characteristics were retrieved from Landsat 7 ETM+ and Landsat 8 TIRS/OLI imageries, acquired on 23 April 2004 and 16 March 2015 over the Seulawah Agam area, respectively. The normalized difference vegetation index (NDVI) threshold method for emissivity retrieval and split-window algorithm for land surface temperature (LST) were utilized. The results show that the vegetation index changes moderately over the geothermal area, especially at the residential area and western side of the volcano which is in line with a fault structure of the Seulimeum segment. We calculated the LST from the thermal bands of Landsat images 2004 and 2015 with approximate results are 28 – 35 °C. The spatial distribution of surface temperatures at the mountain derived from the classified image 2015 varies considerably compared with the classified image 2004. The surface temperature and vegetation index changes indicate a thermal activity at the Seulawah Agam volcano. It can be concluded that the Landsat 7 ETM+ and Landsat 8 TIRS/OLI imageries are potentially used to study the thermal status of the Seulawah Agam geothermal area.

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Aceh is the region that some parts of the Sumatran Fault System (GSF) pass through. The existence of faults has implications for earthquake events. To understand the impact of seismic activities that occur along the fault, it is necessary to do fault mapping and geometry modelling. In this study, magnetotelluric geophysical methods were used to describe 2D resistivity structures in the northern Sumatran. A geophysical survey using magnetotelluric method was done to image 2D resistivity model along the northern part of the fault. The measurement was carried out two lines, with a length of the profile is 92 km and 114 km, consisting of 14 measurement points across the fault, with distances between tracks ranging from 10-15 km. 2D resistivity models were generated by using the Reduce Basic Occam (REBOCC) code. From the resulted model, it can be interpreted as indications of the existence of the Aceh Segment and Segment Seulimeum Faults. In-line C, there are two locations indicated by faults, namely Saree area associated with the Seulimeum segment and the Jantho area associated with the Aceh segment and line D in the geographic area is associated with the Aceh segment. From the resulted model, the Sumatran Fault in the northern part of Aceh was divided into two segments as shown in the model.