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.

ABSTRAK Penelitian kestabilan lereng batuan menggunakan metode analisis kinematik lereng dan klasifikasi massa batuan dilakukan di lereng pinggir jalan Banda Aceh -Calang di Km 17,8 di Kecamatan Lhoknga Kabupaten Aceh Besar. Penelitian ini bertujuan untuk mengetahui jenis longsoran yang akan terjadi di masa yang akan datang, menilai kualitas massa batuan pembentuk lereng, dan tingkat kestabilannya berdasarkan klasifikasi SMR. Akuisisi data struktur massa batuan dilakukan di sepanjang lereng menggunakan metode scanline. Data yang diambil berupa arah kemiringan bidang diskontinuitas, arah bidang, dan kondisi bidang diskontinuitas bidang berupa kemenerusan, kekasaran, bukaan, isian, luahan air dan tingkat perlapukan. Analisis kinematik lereng didapatkan berdasarkan hasil proyeksi stereografi dan analisis kualitas serta kestabilan lereng batuan berdasarkan parameter RMR dan SMR. Hasil analisis kinematik lereng menunjukkan jenis longsoran yang akan terjadi di lereng 1 berupa longsoran baji dan planar. Di lereng 2 dimungkinkan terjadinya longsoran gulingan/toppling karena bidang joint set yang berlawanan dengan arah lereng. Nilai RMR di lereng 1 sebesar 63 dengan kategori batuan Bagus dan RMR lereng 2 sebesar 57 kategori batuan sedang. Nilai SMR terendah di lereng 1 sebesar 29 (kategori Buruk) untuk longsoran planar dan 53 (kategori Sedang) di lereng 2 longsoran gulingan. Lereng 1 memiliki probabilitas kejadian longsor planar sebesar 60%.Kata kunci: kestabilan lereng, analisis kinematik, klasifikasi massa batuan. ABSTRACT

The Indonesian volcano is only limited for the electrical energy capacity, but in developed countries, the volcano is not only used for power plan but also developed for the tourism industry. Jaboi is one of the volcanoes located in Sabang with a capacity of 80 MW. The five potential of geothermal spots can be used as geo-tourism tours. Besides to improve the economic sector, the main purpose of the geo-tourism is the management of the tours that will be provided for educative lessons about the friendly life in a volcanic area. In this paper, we produced the educational videos that placed on each tourist spot; the video contains including the history of the site, geological background, and also information about the risks of living in a volcanic area. The QR code program is used as a medium for data transfer that can be scanned through a smartphone. This application is widely used in tourism as an economical alternative in technology. In the several spots that difficult to access, we also produced a safe route with a QR code program. The tracks will be overlaid on the smartphone with the ‘gpx viewer’ application, which possible to download from Google Play or App Store.

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Lambada Lhok is one of the coastal areas with the most severe water crisis in Aceh Besar, Aceh. Clean water crisis happening in the area because of their breach of saltwater into freshwater aquifers and also due to the large decrease in ground water level that resulted in seawater intrusion. This research was conducted on four lines at two locations, namely: 3 (three) lines in the village of Lambada Lhok and 1 (one) line in the village of Kajhu. Kajhu village was used as comparative data for areas that are free from the intrusion of sea water. The research method using 2D resistivity Wenner-Schlumberger configuration, while the data acquisition using the ARES equipment. Data analysis using Res2Dinv software to make 2-dimension (2-D) cross section model. Lambada Lhok village is an alluvial deposition with an average height of 0-5 meters above sea level (dpl). The subsurface lithology of the village lambada lhok consists of clay sand, sandy clay and clay. Based on the results of the analysis of resistivity values indicate that the suspected sea water intrusion in the village of Lambada Lhok reaches a depth of 29 meters. It can be concluded that the spread of sea water intrusion in Lambada Lhok beginning of the line LL 1, LL 2 to LL 3. Distribution of seawater intrusion are most severe in the trajectory LL 2 and began to decrease at LL 3 trajectory.