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A geohazard assessment was conducted in the Aerotropolis area of the new Yogyakarta international airport, located in the Yogyakarta special region province, Indonesia. The study involved the analysis and modeling of 3-D inversions of earth gravity anomaly data obtained from the high-resolution of Global Gravity Model (GGM). The main objective of the study was to identify subsurface geological structures such as faults, active volcanoes, and sedimentary layers that may pose potential hazards to the Yogyakarta aerotropolis area. The complete Bouguer anomaly in the study region was calculated using modern terrain correction methods that relied on full-scale topography gravity data from the SRTM2gravity model. A 2-D radial spectrum analysis was then performed on this anomaly data, which revealed that the average thickness of sedimentary layers was estimated to be more than 100 m. The rock density contrast was determined using the residual gravity anomaly inversion, which showed a range of - 0.086 g/cm³ to 0.043 g/cm³ . The analysis of gravity anomalies and rock density contrast provided results that aligned with the regional geological conditions of the Yogyakarta region, including the pattern of igneous rock intrusion with high density contrast, the presence of the Merapi magma chambers associated with low negative density contrast, and the Opak normal fault path at low and high contrast boundaries, which could lead to natural hazards in the region. [ABSTRACT FROM AUTHOR]

West Papua province in eastern Indonesia is positioned in a dynamic tectonic zone along with the collision of the Australian, Pacific, and Eurasian plates. The interaction resulted in the formation of strike-slip faults such as Koor, Sorong, Ransiki, and Yapen, that are prone to earthquakes in the region. The rocks of West Papua in the northern part are a contribution to the Pacific Ocean plate consisting of ophiolite and volcanic arcs of the archipelago, even while the rocks of the Australian plate in the southern part are dominated by quaternary and siliciclastic sedimentary. It has a wide variety of resources, including oil and gas. This study combines the interpretation of regional gravity and magnetic data derived from satellite observations to identify the subsurface structure of West Papua. This is performed since most studies were conducted on the surface and did not significantly focus on the subsurface. The composition of subsurface is determined through three-dimensional (3-D) unconstrained inversion modeling using the iterative reweighting inversion of regional gravity and magnetic anomalies as a function of density contrast and magnetic susceptibility of rocks. In depth variations, gravity inversion produces density contrast ranging from − 0.348 to 0.451 gr/cm3, whereas magnetic inversion provides rock susceptibility varying between − 0.363 and 0.223 SI. Gravity and magnetic inversions characterize the subduction of the Pacific Ocean plate in the north, extensive intrusion of igneous rocks, and low density-susceptibility contrast in the Bintuni basin as a source of oil and natural gas. The boundary between the sediment layer and the basement is believed to be 15–20 km deep, with rocks from the uplifted mantle in the north and a Silur-Devon aged Kemum formation in the south. [ABSTRACT FROM AUTHOR]

Radiogenic heat production (RHP) has been investigated from wide types of rocks based on regional setting and metamorphism grade. In this study, we analyze the abundance of heatproducing elements (U, Th, K) and Radiogenic Heat Production (RHP) on I-type and S-type granite rocks in Bangka Island, one of the main provinces in Tin Belt Island. The average U, Th, and K concentrations for both S-type and I-types granite are 10.27 ppm, 79.6 ppm, 3.1%, and 87.79 ppm, 99.2 ppm, and 1.93 % respectively. The highest concentration of U (681.22 ppm) and Th (99.2 ppm) are found in Pangkal Pinang and K (3.79%) in West Bangka. We analyze that the RHP average for I-type granite is higher at 27.87 (N=17, range from 12.97 to 550.28) than S-type with 8.43 (N=11, range from 4.93 to 12.64). The Th/U ratio shows an exponential correlation with RHP and classifies S-type granite tectonic discriminant as continental collision and I-type granite as a continental arc. [ABSTRACT FROM AUTHOR]

Ambon and Seram islands in eastern Indonesia are located in the convergence zone of three major plates, causing this area to have many geothermal manifestations on the surface. A subsurface geological study on Ambon and Seram has been conducted based on the integration of gravity and magnetic inversion modeling to determine the intrusion of igneous rock as a potential source of geothermal energy. The gravity and magnetic inversion utilized gravity and magnetic anomaly data from the World Gravity Map (WGM) and the Earth Magnetic Anomaly Grid (EMAG), as well as the CRUST 1.0 global earth crust model, as the constraints. In general, gravity and magnetic anomalies in the study area are compatible, in which the southern part of Ambon is dominated by high anomalies and the northern part is covered by low anomalies associated with the Seram trench. The high anomaly is thought to be related to the intrusion of igneous rocks underneath the surface that have cooling and are rich in magnetic minerals, while the low anomaly is related to the destruction zone due to subduction in the north of Seram. The gravity inversion shows the distribution of subsurface rock density ranging from 1.86 g cm-3 to 2.82 g cm-3, while magnetic inversion produces rock susceptibility contrast ranging from -0.0034 SI to 0.0058 SI. Based on Curie point depth analysis of magnetic data, the bottom depth of the magnetic source is estimated at 25 km. The 3D subsurface model of Ambon and Seram based on gravity and magnetic inversion shows a massive and evident intrusion pattern with high rock density and susceptibility contrast down to a depth of 10 km. The distribution of high density and susceptibility is thought to have implications for geothermal resources in Ambon and Seram. [ABSTRACT FROM AUTHOR]