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Kadidia is one of the area with geothermal potential in Central Sulawesi, Indonesia. Therefore, this study aims to estimate the depth of reservoir and identify subsurface geological structures using gravity data and power spectrum analysis. It uses secondary data from the field survey results of the geophysical team from the Mineral and Geothermal Resource Center Agency. Furthermore, the data were processed to obtain a complete Bouguer anomaly, reduction in a flat field, regional and residual anomalies. The results of residual anomalies showed high and low values in the range of (5-13) mGal corresponding to volcanic rocks and in the range of -10 to -4 mGal spread evenly in the study area respectively. The analysis of derivative showed the presence of intrusive rocks which are thought to be granite, and the power spectrum showed that the heat source rocks from the geothermal system were inferred as granite at a depth of more than (3.68-6.00) km. In addition, the reservoir rocks were interpreted as low-density sandstones at a depth of (0.80-1.37) km, and a caprock in the form of sandstones with medium density at a depth of (0.20-0.80) km, and from the surface to 0.20 km is soil. The interpretation of three-dimensional modeling showed that the faults control geothermal manifestations, i.e. the Koalarawa and Towingkoloe faults, which extends from northwest-southeast.

Lawanopo Fault is a horizontal shear fault (sinistral strike-slip) found in Southeast Sulawesi province and is thought to be active during Plio-Pleistocene or mid-late Miocene to the present. This study has been carried out which aims to find out the geometric shapes below the surface of the Lawanopo fault using complete Bouguer anomaly (ABL) data. The ABL data is projected onto a flat plane using the Dampney method at an altitude of 8 km, and the separation of local and regional anomalies is carried out using the upward continuation method at an altitude of 60 km. Three-dimensional (3D) modeling under the surface of the Lawanopo fault is done using the computer program Grablox. Data processing techniques using Singular Value Decomposition (SVD) and Occam inversion. The results showed that a high gravity anomaly of 190-225 mGal was caused by an igneous rock below the surface with a density of 2.7-3.33 gr/cm3 and a thickness of about 13 km, a moderate anomaly of 175-187 mGal caused by Paleozoic igneous rocks aged Carbon with a density of 2.6-2.9 gr/cm3 and a thickness of about 25 km. Low anomaly 115-160 mGal is caused by rocks with a density of 2.0-2.5 gr/cm3 and a thickness of about 22-23 km. The Lawanopo fault constituent rocks consist of alkaline rocks in the basement covered by sediment and metamorphic with a depth of Lawanopo fault more than 15 km and begin to be seen at a depth of 4.3 km of the surface. it is known that the area around the Lawanopo fault is an area prone to earthquakes. But, based on the soil and rock structure around the Lawanopo fault, the compactness and attenuation levels in reducing earthquake waves are quite good, so that land use around the Lawanopo fault tends to be safe.

The geothermal field of Suli and Tulehu is located in the eastern part of the Ambon Island, administratively situated in central Maluku regency, Maluku province, Indonesia. In the year 2017, the measurement of the Earth’s gravity and magnetic field has been done to evaluate the geothermal system in Suli and Tulehu. The application of gravity and magnetic methods was applied to determine the subsurface geological model describing geothermal sources, reservoirs, and faulting as a fluid conduit in the study area. Bouguer anomalies are positive in the range from 93 to 105 mGal, while magnetic anomalies are negative to positive in the range from − 656 to 310 nT, generally southwest to northeast. Geothermal manifestations in the form of hot springs associated with low residual Bouguer and magnetic anomalies positioned on the Banda-Hatuasa, Banda, and Huwe fault lines related to the alteration zone. Euler deconvolution analysis of the complete Bouguer anomaly data shows the maximum depth of fault detected at 1200 m. Gravity and magnetic inversion show high density and susceptibility contrast of rocks associated with Eriwakang and Simalopu pyroclastic rocks as geothermal sources. Low density and susceptibility contrast is estimated to be geothermal reservoirs due to interactions with geothermal source rocks below. A geological conceptual model based on the inversion modeling of gravity and magnetic data provides clear and comprehensive information on the geothermal systems in Suli and Tulehu, Ambon, the eastern part of Indonesia.

In early 2017, the geothermal system in the Suli and Tulehu areas of Ambon (Indonesia) was investigated using a gravity gradient tensor and analytic signal. The gravity gradient tensor and analytic signal were obtained through forward modeling based on a rectangular prism. It was applied to complete Bouguer anomaly data over the study area by using Fast Fourier Transform (FFT). The analysis was conducted to enhance the geological structure like faults as a pathway of geothermal fluid circulation that is not visible on the surface because it is covered by sediment. The complete Bouguer anomaly ranges of 93 mGal up to 105 mGal decrease from the southwest in Suli to the northeast in Tulehu. A high gravity anomaly indicates a strong magmatic intrusion below the Suli region. The gravity anomalies decrease occurs in the Eriwakang mountain and most of Tulehu, and it is associated with a coral limestone. The lower gravity anomalies are located in the north to the northeast part of Tulehu are associated with alluvium. The residual anomaly shows that the drill well TLU-01 and geothermal manifestations along with the Banda, and Banda-Hatuasa faults are associated with lowest gravity anomaly (negative zone). The gravity gradient tensor simulation and an analytic signal of Suli and Tulehu give more detailed information about the geological features. The gzz component allows accurate description of the shape structures, especially the Banda fault associated with a zero value. This result will be useful as a geophysical constraint to subsurface modeling according to gravity gradient inversion over the area.

Wilayah Hargosari terletak di daerah karst Gunungsewu yang dikenal sebagai daerah subur dan kurang air terutama selama musim kemarau. Secara geologis, tersusun oleh batu gamping yang berpotensi menyebabkan sungai bawah tanah sebagai akibat dari proses pelarutan. Metode VLF-EM digunakan untuk mengetahui pola sungai bawah tanah terkait dengan kontras parameter fisik konduktif yang disebabkan oleh keberadaan air di lubang batugamping. Tujuan dari penelitian ini adalah untuk menentukan jejak dan pola sungai bawah tanah Bribin serta pemodelannya menggunakan perangkat lunak lnv2DVLF. Interpretasi kualitatif dilakukan berdasarkan pada pengolahan data yang telah dikoreksi topografi menggunakan filter moving average dan filter Karous-Hjelt, sedangkan interpretasi kuantitatif menggunakan program lnv2DVLF dan divisualisasikan menggunakan Surfer 12. Berdasarkan interpretasi kualitatif dan kuantitatif, dapat disimpulkan bahwa sungai bawah tanah Bribin mengalir dari arah timur ke barat melalui wilayah Hargosari, dan terdiri dari dua aliran sungai bawah tanah yang saling berhubungan. Lebar area konduktif adalah (25 ± 5) m pada kisaran kedalaman sekitar 148-184 m.

The specific goal of this work is to present a complete velocity map obtained by picking the velocity in Common Image Gather (CIG) map. We simulated a shot gather in order to obtain a synthetic travel time data for depth analysis. We successfully determined the correct migration velocity and presented the velocity interval model. For further study, we also conducted a Semblance analysis in order to obtain a coherency panel between the energy and the depth migration velocity analysis. We successfully interpreted the conventional semblance profile that the correct velocity model maximizes that energy which is represent higher value. For the real case, The data set was acquired by CGGVeritas in 2009 of RMS velocities recorded in 48 CMP points. The results of the semblance analysis shows well coherence with the seismic reflectance data that reveals the Low Velocity Zone of Sumatra fault related to the present of fluid and gas.

Pegunungan Bintang district with the capital Oksibil, almost all of its territory is mountains of karst, especially in the west area, people living in the mountain slopes and small valleys in small groups, scattered and isolated. Karst areas, in general, has a lot of subsurface cavities at a developed stage to form subsurface rivers. Therefore, as the capital of the District Oksibil need to know the local subsurface conditions, how much growth cavities that exist in Oksibil. So that the study was carried out by very low frequency electromagnetic (VLF) method. Based on the field measurement and VLF data analysis, the interpretation and the dolina correlation, the Oksibil area is still safe, by considering that there is no indication of dolina or subsurface river that continued relatively horizontal, and the subsurface doline at relatively quite deep (> 40 meters). electromagnetic method (VLF). The subsurface conditions is related to the presence of cavities in subsurface interconnected, while at the surface will be developed some physical facilities and others settlement building and district offices. So, given the limited surface condition that can be developed, being a good construction site is quite difficult in Pengunungan Bintang. Mapping the subsurface condition associated with the presence of cavities under the ground, for the sake of securing the future development planning on the surface that it needs supports the analysis of regional development policies in particular Oksibil district, Pegunungan Bintang, Papua province . Geophysical method uses principles of physics to study the earth. Almost all geophysical methods have been used to explore the existence of natural resources for the benefit of humans , such as oil and gas, mining materials, ground water, sources of geothermal energy and others. Geophysical method is generally performed in order to determine the existence of anomalous rock, position of the system, dimension and physical properties of the anomaly

Denpasar City and its vicinity considered as the areas with excessive ground water exploitation and high earthquake intensity. These conditions will cause these area potential with land subsidence which is triggering ground fissures. This research aims are to mapping the fissures potential areas based on microtremor measurement in Denpasar City and its vicinity. Ground fissures will happen if the land subsidence occurs in the areas which have different bedrock height beneath its sedimentary layer. The height of bedrock is determined by reducing surface elevation with the sedimentary layer thickness. This sedimentary layer thickness obtained from microtremor measurement using HVSR method, and Shear wave velocity (VS) obtained from microtremor array measurement which is analyzed by Spatial Auto Correlation (SPAC) method. The result from HVSR method as well as Peak Ground Acceleration (PGA) value are then analyzed to get ground shear strain value, which is the soil surface strain and its effect when earthquake occurs. Based on the bedrock map, it can be estimated that the bedrock layer forms structure in the southern part of the research areas and the potential fissuring area due to the massive ground water exploitation is in the west Denpasar Subdistrict. In addition, based on the bedrock map and ground shear strain value which combined with Simple Additive Weight (SAW) method, there are two areas having Assuring potential, i.e west and south Denpasar Subdistricts.