Geothermal Reservoir Identification based on Gravity Data Analysis in Rajabasa Area- Lampung

Gravity research in the Rajabasa geothermal prospect area was conducted to determine geothermalreservoirs and faults as reservoir boundaries. The research includes spectrum analysis and separation of the Bouguer anomaly to obtain a residual Bouguer anomaly, gradient analysis using the second vertical derivative (SVD) technique to identify fault structures or lithological contact, and 3D inversion modeling of the residual Bouguer anomaly to obtain a 3D density distribution subsurface model. Analysis was performed based on all results with supplementary data from geology, geochemistry, micro-earthquake (MEQ) epicenter distribution map, and magnetotelluric (MT) inversion profiles. The study found 3 (three) geothermal reservoirs in Mount Balirang, west of Mount Rajabasa, and south of Pangkul Hot Spring, with a depth of around 1,000-1,500 m from the ground level. Fault structures and lithologies separate the three reservoirs. The location of the reservoir in the Balirang mountain area corresponds to the model data from MEQ, temperature, and magnetotelluric resistivity data. The heat source of the geothermal system is under Mount Rajabasa, which is indicated by the presence of high-density values (might be frozen residual magma), high-temperature values, and the high number of micro-earthquakes epicenters below the peak of Mount Rajabasa.

Chronostratigraphy of blue ice at the Larsen Glacier in Northern Victoria Land, East Antarctica

Blue ice areas (BIAs) allow for the collection of large-sized old ice samples in a cost-effective way because deep ice outcrops and make old ice samples available close to the surface. However, most chronostratigraphy studies on blue ice are complicated due to fold and fault structures. Here, we report a simple stratigraphy of ice from the Larsen BIA, Antarctica, making the area valuable for paleoclimate studies. Ice layers defined by dust bands and ground penetration radar (GPR) surveys indicate a monotonic increase in age along the ice flow direction on the downstream side, while the upstream ice exhibits a potential repetition of ages on scales of tens of meters, as shown in the complicated fold structure. Stable water isotopes (δ18Oice and δ2Hice) and components of the occluded air (i.e., CO2, N2O, CH4, δ15N-N2, δ18Oatm (= δ18O-O2), δO2/N2, δAr/N2, 81Kr and 85Kr) were analyzed for surface ice and shallow ice core samples. Correlating δ18Oice, δ18Oatm, and CH4 records of Larsen ice with existing ice core records indicates that the gas age at shallow coring sites ranges between 9.2–23.4 ka BP and ice age for entire surface sampling sites between 5.6–24.7 ka BP. Absolute radiometric 81Kr dating for the two cores confirms the ages within acceptable levels of analytical uncertainty. Our study demonstrates that BIA in northern Victoria Land may help researchers obtain high-quality records for paleoclimate and atmospheric greenhouse gas compositions through the last deglaciation.

VOLUMETRIC AND SPATIAL SEGMENTATION OF THE TIEN SHAN LITHOSPHERE ACCORDING TO GEOPHYSICAL DATA

This article consolidates the results of studying the deep structure of the lithosphere of the Central Tien Shan, which aimed to identify the main tectonic elements in its geophysical models. We have compared the structural and geological data with the information on the deep structure obtained by geophysical methods and from the positions of earthquake hypocenters in the study area. According to geological concepts, the Tien Shan orogenic belt is characterized by longitudinal and transverse segmentation. The boundaries of the Northern, Middle, Southern Western and Eastern segments of the Tien Shan are deep-seated fault structures. In deep faults and channels of heat and mass transfer, endogenous processes are localized. High-velocity, geoelectrical and thermal models consider such faults and channels as contrasting objects that can be referred to as indicators of these processes.Our analysis of the locations of earthquake hypocenters from NNC, KNET, CAIIG, KRNET, SOME catalogues shows that seismic events are strongly confined to the fault zones and the boundaries of large blocks. A correlation between the anomalies of geophysical fields suggests the degree of inheritance of tectonic structures and the boundaries of the main tectonic segments of the Tien Shan. To compare the crustal and upper mantle heterogeneities reflected in different geophysical fields, we have analyzed seismic tomographic sections based on volumetric seismotomographic models geoelectric and velocity sections along profiles across the main tectonic elements of the study area. The sections are used to identify the zones with relatively low (i.e. reduced) seismic wave velocities and detect the deep-seated longitudinal segmentation of the folded belt. Objects showing anomalous seismic wave velocities are found in the seismotomographic sections at all the depths under consideration. The most contrasting differences in the velocities of P- and S-waves are typical of the depths of 0-5 km and 50-65 km, showing the most clearly observed Northern, Southern and Western segments of the Tien Shan. In general, the velocities of P- and S-waves at the Northern Tien Shan are higher than those at the Middle and Southern segments. We have analyzed the distribution of geoelectric heterogeneities identified from magnetotelluric sounding data in order to determine the boundaries of the main tectonic elements that are considered as the zones of increased electrical conductivity confined to the boundaries of the fault structures. The distribution of earthquake epicenters clearly reflects the segmentation of the Tien Shan into the Northern, Middle and Southern segments and shows the Western and Eastern Tien Shan relative to the Talas-Fergana fault. Ourstudies of the crust and the upper mantle of the Tien Shan have confirmed that the abovementioned tectonic segments have differences in their deep structures Based on a comprehensive analysis of the study results, we can qualitatively identify a relationship between the distribution of the velocity and geoelectric heterogeneities in the crust and upper mantle, seismicity and the stress-strain state of the crust.

Research on Automatic Construction Method of Three-Dimensional Complex Fault Model

Three-dimensional complex fault modeling is an important research topic in three-dimensional geological structure modeling. The automatic construction of complex fault models has research significance and application value for basic geological theories, as well as engineering fields such as geological engineering, resource exploration, and digital mines. Complex fault structures, especially complex fault networks with multilevel branches, still require a large amount of manual participation in the characterization of fault transfer relationships. This paper proposes an automatic construction method for a three-dimensional complex fault model, including the generation and optimization of fault surfaces, automatic determination of the contact relationship between fault surfaces, and recording of the model. This method realizes the automatic construction of a three-dimensional complex fault model, reduces the manual interaction in model construction, improves the automation of fault model construction, and saves manual modeling time.

Structures and Kinematics of the Huanghua Depression in Bohai Bay Basin, East China: Implications for the Formation Mechanism of a Transtensional Basin

The Bohai Bay Basin in East Asia is a rift basin created by Cenozoic subduction of the oceanic Pacific plate beneath the Asia continent. Many prior studies suggest that the basin was initially formed in the Paleocene with the development of several NNE-trending extensional grabens, but subsequently impacted by right-lateral shear along these existing NNE-trending structures in the middle Eocene, transforming the Bohai Bay Basin into a transtensional basin and producing EW-trending grabens in the Bozhong and the northeastern Huanghua depressions. However, how this transformation occurred remains to be fully understood. Based on seismic and drilling data, we herein investigated the fault structures, basin architecture, and evolutionary stages of the Huanghua Depression in the central-west Bohai Bay Basin to examine the strain partitioning and evolution mechanism during the Paleogene syn-rifting stage. The results reveal that the Huanghua Depression is composed of three structurally distinctive zones, namely, a dextral transtensional, a NW-SE extensional, and a N-S extensional zones from southwest to northeast, which are separated from each other by two transfer zones. The NW-SE extensional zone is interpreted as a horsetail structure on the northern termination of the dextral transtensional zone. This dextral transtensional zone and the Tan-Lu Fault zone to the east served as strike-slip boundaries within which EW-trending depressions such as the northeastern Huanghua and Bozhong depressions formed in the middle Eocene.

Discussion on a methodology for the digital reconstruction of complex fault structures in coal mines

The visualization of complex geological structures can provide technical support for accurate prediction and prevention of coal mine disasters. Taking fault structure as an example, this study proposes a new digital reconstruction method to realize the visualization of geological structure. The methodology for the digital reconstruction of complex fault structures is composed by the following four aspects, including collection and fidelity of multi-physical field data of fault structure, transmission of multi-physical field data, multi-physical data normalization and digital model of fault structures. The key scientific issues of this methodology to be resolved includes in-situ fidelity of multi-field data and normalized programming of multi-source data. In addition, based on the geological conditions in Da 'anshan coal mine in the mining area of western Beijing, China, this paper makes a preliminary attempt to establish a digital model of fault and fold structures by this methodology.

Novel Bathymetry of Lake Afdera Reveals Fault Structures and Volcano-Tectonic Features of an Incipient Transform Zone (Afar, Ethiopia)

Lake Afdera is a hypersaline endorheic lake situated at 112 m below sea-level in the Danakil Depression. The Danakil Depression is located in the northern part of the Ethiopian Afar and features an advanced stage of continental rifting. The remoteness and inhospitable environment explain the limited scientific research and knowledge about this lake. Bathymetric data were acquired during 2 weeks expeditions in January/February 2016 and 2017 using an easily deployable echosounder system mounted on an inflatable motorized boat. This study presents the first complete bathymetric map of the lake Afdera. Bathymetric results show that the lake has an average depth of 20.9 m and a total volume of 2.4 km3. The maximum measured depth is 80 m, making Lake Afdera the deepest known lake in Afar and the lowest elevation of the Danakil Depression. Comparison with historical reports shows that the lake level did not fluctuate significantly during the last 50 years. Two distinct tectonic basins to the north and the south are recognized. Faults of different orientations control the morphology of the northern basin. In contrast, the southern basin is affected by volcano-tectonic processes, unveiling a large submerged caldera. Comparison between the orientation of faults throughout the lake with the regional fault pattern indicates that the lake is part of two transfer zones: the major Alayta–Afdera Transfer Zone and the smaller Erta Ale–Tat’Ali Transfer Zone. The interaction between these Transfer Zones and the rift axis forms the equivalent of a developing nodal basin which explains the lake’s position as the deepest point of the depression. This study provides evidence for the development of an incipient transform fault on the floor of the Afar depression.