Complete Bouguer Anomaly Research Articles

Do gravity data justify a rifted “Liguro-Provençal Basin”?

The geodynamic evolution of the Liguro-Provençal Basin and its crust and upper mantle structure remain debated, especially regarding the role of rifting in continental break-up and seafloor spreading. Our study incorporates updated datasets, including new gravity maps from the AlpArray Gravity Working Group (complete Bouguer, free air, and isostatic anomalies) for 3D modeling and gravity field analysis, seismic data from Lobster offshore campaigns for direct comparison, and geodynamic models, supplemented by seismic profiles from previous French and Italian campaigns to constrain the interpretation. We used GFZ’s IGMAS + software for interactive 3D modeling, creating a density model extending to 300 km depth that includes crustal and upper mantle inhomogeneities based on prior geodynamic models. This hybrid approach, with polygonal structures for the crust and voxels for the upper mantle, clarifies individual contributions to the gravity field. Extending initial gravity modeling from the SPP MB4D project INTEGRATE, our work provides a consistent 3D density model for the Alps and Ligurian Basin. The constrained 3D modeling and numerical analyses (terracing, clustering, filtering, curvature), along with vertical stress and gravitational potential energy calculations, suggest that rifting has significantly influenced the basin’s geological evolution.

ANALYSIS OF SUBSURFACE STRUCTURE OF BANDAR LAMPUNG CITY BASED ON GRAVITY ANOMALIES

Bandar Lampung City is located at the southeastern tip of Sumatra Island, an area highly prone to earthquake and tsunami disasters. Along the Sumatra Island, there are seismic faults stretching along the Bukit Barisan Mountains. In the Bandar Lampung region, one of these faults is the Panjang Lampung fault. Gravity methods are commonly used to identify subsurface structures based on variations in rock density. This study aims to identify the subsurface structure of Bandar Lampung City based on gravity anomaly modeling, both 2D and 3D models. The research consists of three main stages: data correction, data processing including spectrum analysis, moving average, second vertical derivative analysis, and subsurface structure modeling. The complete Bouguer anomalies in the study area range from 41.9 mGal to 73.3 mGal. Modeling results indicate the presence of structures such as the Panjang Lampung fault in the Northeast and a graben in the Central region, verified through SVD analysis and geological information. The existence of the Panjang Lampung fault, classified as an active fault, along with volcanic pyroclastic rocks and significant sediment layers in the central region, makes the research area potentially susceptible to the impact of amplification in the event of an earthquake disaster.

2D INVERSION MODELING OF OIL AND GAS BASINS USING GRAVITY DATA IN TAMBELANG DISTRICT

Pertamina Hulu Energi discovered a new source of oil and gas reserves in Tambelang, Bekasi Regency, which was named East Pondok Aren (EPN-001). These oil and gas reserves have great potential based on the oil flow test in the second Drill Stem Test. The drill data needs to be correlated with other supporting data such as geophysical methods to ensure the accuracy. Therefore, this research was conducted to examine the subsurface structure of oil and gas reserves in EPN-001 through 2D inversion modeling using the gravity method. Gravity satellite data was taken via the GGMPlus website with a total of 23,898 data in the form of gravity disturbance, geoid, and topography, so only terrain and bouguer corrections were carried out to get the Complete Bouguer Anomaly value. The research results show low anomaly values from -0.4463 – (-0.0339) mGal which are thought to be associated with alluvium lithology and the Lower Cibulakan Formation. In the 2D model, it can be seen that the drilling point in the Lower Cibulakan Formation layer has a density contrast value of -0.002 – 0.001 g/cc at a depth of 2590 m, and is known to be a reservoir that stores hydrocarbon reserves in the research area.

Identifying the structure as a hot water outflow path using gravity in Jatimulyo, South Lampung

Abstract Geothermal manifestations have been utilized as a tourist attraction (geo-tourism) worldwide. Geothermal manifestation systems could be found in many forms such as hot springs. The path of the hot water flow is controlled by the existence of geologic structures such as faults as the medium. Geophysical methods in general have been used to image and characterize subsurface layers. The gravity method using the natural source has been employed to determine the geological structure, such as faults. This study aims to identify the structure related to the outflow path which is part of the geothermal system using gravity method in Jatimulyo Village, Jati Agung, South Lampung. The result shows the contrast anomaly indicating the existence of a fault that could be a hot water path. An outflow zone which is characterized by low temperatures because it is far from heat sources. The complete Bouguer Anomaly is used to create 2D forward modelling where the model is divided in 2 layers. The first layer is indicated as Lampung Formation (QTl) with density of 1.8 g/cc, and second layer recognized as bedrock with denser rock of 2.78 g/cc representing Tertiary Paleozoic (Pzg) Gunung Kasih Complex Formation.

Analysis of gravity anomaly data for identification of mineral distribution prospects in the Kuta Cot Glie area, Aceh Besar

Abstract Gravity anomaly data was analyzed using the gravity method to obtain variations in gravity values and to identify mineral distribution prospects in the Kuta Cot Glie area, Aceh Besar. The Scintrex CG-5 gravimeter instrument was used to measure gravity data. After being corrected and receiving complete Bouguer anomaly values, the variation in gravity values from the research location was shown to be in the range 75-126 mGal. There are two anomalies within gravity values that are higher and lower than the surroundings. The first one is the distribution of serpentine minerals (2.4 – 3.10 g/cm 3) with variations of 108-126 mGal. This serpentine mineral is located at the center of the research location with a total area of ± 67,500 m 2. The second anomaly is limonite mineral deposits (1.55-1.7 g/cm3) with variations in gravity values of 75-87 mGal. The limonite were found on the East and West sides of the location, with a distribution area of ±71,250 m 2. The mineral deposit of limonite is a result of weathering from serpentinite rocks, therefore, the location of limonite mineral deposits is lower than the location of serpentinite. These results are aligned with the geological conditions which is dominated by serpentinite ultramafic metamorphic rocks.

Gravity Interpretation of Mud Volcano based on Satellite Data (Study Case Kuwu and Cangkring Mud Volcano)

<p class="Abstract">A mud volcano is one type of mountain in the world. Mud volcano has specific characteristics. In Java, several mud volcanoes spread from west to east of Java. Bledug Kuwu and Bledug Cangkring are mud volcanoes in Central Java. Research on the Bledug Kuwu and Cangkring mud volcanoes systems was not done. In this preliminary study, the gravitational field analysis of the Kuwu-Cangkring mud volcano system was done by using GGmPlus satellite data with a 220 m grid and elevation data using ERTM. Free air anomaly data processing obtained a complete Bouguer anomaly value of 23 to 34 mGal. The separation process of anomalies using the upward continuation method produces a local of -0.5 to 0.5 mGal and a regional of 23 mGal to 34 mGal. The local anomaly value of Bledug Kuwu was -0.275 to - 0.05 mGal and Bledug Cangkring-0.125 to 0.1 mGal. The local anomaly around Bledug Cangkring is higher than Bledug Kuwu, indicating a lower density beneath Bledug Kuwu than in Cangkring.</p>

Assessments of Gravity Data Gridding Using Various Interpolation Approaches for High-Resolution Geoid Computations

This article investigates the role of different approaches and interpolation methods in gridding terrestrial gravity anomalies. In this regard, first of all, simple and complete Bouguer anomalies are considered in gravity data gridding. In the comparison results of gridding these two Bouguer anomaly datasets, the effect of the high-frequency contribution of topographic gravitation (by means of the terrain correction) is clarified. After that, the role of the used interpolation algorithm on the resulting grid of mean gravity anomalies and hence on the geoid modeling accuracy is inspected. For this purpose, four different interpolation methods including geostatistical Kriging, nearest neighbor, inverse distance to a power (IDP), and artificial neural networks (ANNs) are applied. Here, the IDP and nearest neighbor methods represent simple-structured algorithms among the interpolation methods tested in this study. The ANN method, on the other hand, is preferred as a complex, optimization-based soft computing method that has been applied in recent years. In addition, the geostatistical Kriging method is one of the conventional methods that is mostly applied for gridding gravity data in geodesy and geophysics. The calculated gravity anomalies in grids are employed in high-resolution geoid model computations using the least squares modifications of Stokes formula with additive corrections (LSMSA) technique. The investigations are carried out using the test datasets of Auvergne, France that are provided by the International Service for the Geoid for scientific research. It is concluded that the interpolation algorithms affect the gravity gridding results and hence the geoid model determination. The ANN method does not provide superior results compared to the conventional algorithms in gravity gridding. The geoid model with 4.1 cm accuracy is computed in the test area.

Preliminary Study of Subsurface Geological Setting Based on the Gravity Anomalies in Karangrejo-Tinatar Geothermal Area, Pacitan Regency, Indonesia

As per the Geothermal Potential Book published by the Ministry of Energy and Mineral Resources (MEMR) in 2017, Pacitan Regency in East Java Province, Indonesia, has the potential for geothermal energy. Two hot spring manifestations, namely, Karangrejo and Tinatar, located in the Arjosari and Punung districts of Pacitan Regency, respectively, have a combined resource of 25 MWe. We acquired ground-gravity data and evaluated gravity anomalies to explore the underlying geological structure in order to understand the geothermal system behind these manifestations. The results of the study show that the gravitational anomaly in the Karangrejo-Tinatar region ranges from 163 to 176 mGal. Additional analysis of the complete Bouguer anomaly (CBA) map, first horizontal derivative (FHD) map, and field observations points to the existence of three NW-SE trending faults. Two of the faults, which are the Karangrejo fault and the Tinatar fault, may be the flow paths for the manifestation of Karangrejo and Tinatar hot springs.

Re-evaluation of a geothermal system model based on high-resolution gravity field inversion: A case study of the Maritaing geothermal field, Alor Regency, East Nusa Tenggara Province, Indonesia

The Maritaing region in East Nusa Tenggara Province, Indonesia, offers significant geothermal potential for direct power generation and use. This study aims to re-evaluate the geothermal system model in the Maritaing geothermal field using high-resolution gravity inversion. High-resolution gravimetric data were collected using satellite observations and data processing techniques, allowing a better understanding of the subsurface geological structure and density distribution of rocks associated with the geothermal reservoir. This study applied data corrections to acquire complete Bouguer anomalies, gravity gradient analysis to detect geological structures, and inversion modeling of residual gravity anomalies to predict subsurface rock density distribution. The complete Bouguer anomalies exhibit positive values ranging from 70 to 140 mGal and have a northwest–southeast orientation, indicating the existence of andesitic lava and pyroclastic volcanic rocks. Gravity gradient analysis determines the geological structures, such as faults or fractures, used as conduits to create Kura Hot Springs. The model provides useful insights into geological occurrences, such as faults, rock layers, and reservoir accumulations that support geothermal fluids. Based on the present study’s findings, we provide recommendations for developing and managing geothermal resources in the Maritaing area.

Delineation of geological structures of Arta geothermal prospect in Djibouti based on the gravity data analysis and interpretation

The Arta geothermal prospect is located in the southern part of the Gulf of Tadjoura, 45 km west of Djibouti city. This study uses 398 gravity data stations collected by the Djiboutian Office for Geothermal Energy Development (ODDEG) from February to May 2018. The geothermal activity of the Arta area is revealed by surface thermal manifestations, such as near-boiling fumaroles (98 °C). This study aims to delineate the subsurface geological structures responsible for surface geothermal manifestations and define the depth and geometry of the geothermal reservoir in the study area. A Complete Bouguer anomaly was obtained using a Bouguer density of 2.55 g/cm3, derived as an average density from the F-H, G-H and CVUR methods. A regional and residual anomaly trend separation method was applied to focus on the structures of interest in the study area, and a residual Bouguer anomaly map was obtained. Edge detection filters, including Horizontal Derivatives (HD) and an Improved Normalized Horizontal tilt angle (INH), were used to examine the gravity data for edge identification. The density was then modelled in three-dimensional (3-D), utilizing the VOXI Earth Modeling Tool performed in Geosoft Oasis Montaj. The model was constrained using estimated lower (-0.35 g/cm3) and upper (0.65 g/cm3) bound density values from the expected density values of the local geology. The Bouguer and residual anomaly maps show a high-density body in the central part, surrounded by low-anomaly structures. The high-density body is interpreted as an intrusive body covering the basement of the study area. The anomalies imaged from HD and INH indicate a significant number of high gradient anomalies trending N-S, NE-SW, and NW-SE, corresponding to the trend of the geological structures of the Arta geothermal prospect. These high-gradient anomalies can be interpreted as faults, contact zones, or geological boundaries. The 3-D model imaged a high-density anomaly trending N-S in the central part at 2 and 3 km below sea level with a volume of about 126 km3 and an average block density of 2.66 g/cm3, interpreted as magma intrusion or intrusive volcanic rocks. The 3-D vertical cross-sections revealed that the intrusion is visible at depth and that some intrusions could be seen at the surface and near surface. The findings of this gravity study will contribute to the overall and future geothermal exploration and development of the Arta geothermal prospect.

Identifying Potential Areas for Oil and Gas Well Location Planning Using Support Vector Machine Algorithm

To fulfill national energy needs for the National Energy Grand Strategy (GSEN), it is necessary to increase the productivity of oil and gas exploration by involving technology that provides alternative solutions, cuts work time, and overcomes the risk of failure. This research aims to identify potential areas for planning new oil and gas well locations using a machine learning algorithm called Support Vector Machine (SVM). This research chooses four splitting ratios of 80:20, 75:25, 60:40, and 50:50 on training and testing data to produce four models and to identify the most robust model for Blora Regency. The algorithm involves fourteen conditioning parameters comprising altitude, slope, aspect, distance from the river network, land cover, distance from the road network, soil type, Normalized Difference Vegetation Index (NDVI), clay mineral index, iron oxide index, surface temperature, complete Bouguer anomaly (CBL), distance from the fault, and rock type. This research uses the confusion matrix and the ROC-AUC to evaluate all models and determine the best one. The result witnesses the best model is SVM 75:25 with an accuracy (Acc), sensitivity (Sen), specificity (Spe), and predictive value (PPV) of 0.8333; Matthew’s correlation coefficient and Cohen’s kappa of 0.6667; and area under the curve (AUC) of 0.9444. In addition, the conditioning parameter contributing the most significant influence on the best model is the slope equal to 100%.

Subsurface Interpretation of the Sembalun Area, East Lombok using the Gravity Method

The Sembalun area in UTM coordinates is located atEast hanging 452120,3 to 437998,9 and Northing 9062924 to 9085495 and belongs to the UTM 50S zone which is located on Lombok Island, West Nusa Tenggara. The purpose of this study is to determine the presence of subsurface geological structures in the Sembalun area, East Lombok. The geophysical method used in this research is method gravity namely by finding the distribution of density values and finding values Complete Bouguer Anomaly (CBA) which will be used to perform 2D modeling of subsurface geological structures in the study area using software Grablox. The data used in this research is secondary data in the form of GGMplus 2013 satellite imagery data gravity disturbance and Earth Residual Terrain Model (ERTM2160). The results obtained from this study include the rock density obtained by the parasnis method of 2.815 g/cm3. The fault structure is in the North to Southwest of the study area and there is also a caldera in the middle of the study area (between Sembalun Bumbung and Sembalun Lawang). Manifestations in the form of hot springs are in the south (close to Mount Pusuk). The results of 2D modeling with Grablox are dominant with high density indicating that the study area is dominated by andesitic lava rock.

GROWTH-23: An integrated code for inversion of complete Bouguer gravity anomaly or temporal gravity changes

A new code for gravity inversion is freely available. It can be used to work with data on complete Bouguer anomaly (CBA) and temporal gravity changes (dg), and is derived from several previous independent codes for CBA data inversion (GROWTH gravity inversion) and for gravity inversion of dg data (GROWTH-dg). This methodology enables the recovery of general 3D structures for anomalous density as a free aggregation of small parallelepiped cells filled with an adjusted density contrast. The non-linear problem is solved by exploration of the model space. This new code offers the following interesting advantages: (a) integrated approach for working indistinctly with CBA or dg data, (b) only one code to run, even for further graphical presentations, (c) only a limited number of necessary parameters, having all of them suggested default values, (d) ample graphical information on the running screen, and (e) can be run instantly. We describe the new code and its parameters and possibilities, together with some operational aspects. Several test cases are included. The GROWTH-23 code can be freely downloaded from the GROWTH-23_software repository at github.com, under an open source license.

Utilization of Satellite Gravimetric Data to Estimate the Location of the Magma Chamber of Slamet Volcano, Central Java, Indonesia

Satellite gravimetric data can be utilized to map the gravity anomaly on the earth's surface, especially for difficult, extreme, and large areas. In this study, satellite gravimetric data has been used to estimate the location of the magma chamber of Slamet volcano, Indonesia. Information on the magma chamber is very useful for knowing the volcanic characteristics and activity, thus helping pre-mitigation efforts to catastrophic eruptions that occur. The stages in the study which have been carried out include data access, correction, reduction, modeling, and interpretation. The satellite gravimetric data that has been accessed is GGMplus data. After several corrections and reductions are done, the complete Bouguer anomalies (CBA) data are obtained with values ranging from 11.889 – 117.429 mGal. Filtering process using the upward continuation has been applied to obtain regional anomalies data. The regional anomalies data are corrected to the CBA data, so that the residual gravity anomalies data are obtained. The lowest gravity anomaly value is located at positions of 109.21967 E and 7.24281 S which is interpreted to be the location of the magma chamber of Slamet Volcano that is currently still active. The result of modeling of the residual gravity anomalies data indicate that the position of the magma chamber of Slamet Volcano is estimated to be relatively under the cone with a density lower than the surrounding rock densities, i.e. 1.50 – 1.75 g/cm3. The study results have a good match with the geological map of the study area.

Subsurface Analysis on Ranu Grati Lineaments with Satellite Gravity Data

The lineaments with NE-SW direction formed by the Umbulan Spring, Banyubiru Spring, and Ranu Grati Maar in Pasuruan Regency indicate a geological structure. This structure is predicted to play a role in forming these springs and maar. Therefore, a study was conducted to identify the presence of these geological structures using the GGMPlus satellite gravity data. The data used in this study were 945 points with spacing intervals of about 200 to 300 meters. Satellite gravity data needs to be corrected so that the Complete Bouguer Anomaly (CBA) value is obtained, which can be used to determine the distribution of density contrast values ​​in the research area. Gridding is done by using a Second Vertical Derivative (SVD) filter to determine existing fault that results in the lineaments of the two springs and maar based on the second derivative value from CBA. It was found that the range of interpolated CBA values ​​in the study area was around 143 mGal to 150 mGal. SVD analysis indicates existing a fault plane exists through Umbulan Springs, Banyubiru Springs, and Ranu Grati Maar with E-W direction.

Analysis of Formation Ronggojalu Spring and Probolinggo Active Fault Continuity with Satellite Data Gravity Method

The Ronggojalu spring, with a discharge intensity of more than 3,000L/second, makes it one of the spring with the most significant discharge in Indonesia and is the main supplier of clean water for the City of Probolinggo. From the observation of topographic maps, the existence of this spring forms a lineament with Paras Spring and Sumber Kramat with a direction of Northeast to Southwest. The presence of this lineament can indicate the existence of geological structures that play a role in the formation of spring. In addition, this lineament is in the same direction as the active Probolinggo fault identified by PUSGEN (Pusat Studi Gempa Nasional). This study aims to identify the presence of geological structures in the lineament using satellite gravity data GGMplus (Global Gravity Model) and Remote Sensing. This data is quite efficient and effective in identifying subsurface geological structures. With the SVD (Second Vertical Derivative) analysis, the residual anomaly results from the second derivative value of the Bouger anomaly so that it can show the density contrast value as an indication of the geological structure. From the results of the interpolation of satellite gravity data in the study area, the CBA (Complete Bouguer Anomaly) value range is -16.8 – 4.8 mGal. The analysis of SVD and FHD shows a significant contrast different values along the fault line that passes through the spring. The lineament density processing also shows a weak zone around the fault zone, indicating the continuity in that zone. The existence of a fault under this spring indicates the influence of the fault on the formation of Ronggojalu Spring, Paras Spring, and Keramat Spring. In addition, it is estimated that this fault is a continuation of the active Probolinggo fault.

Integrative Analysis of the Geothermal Structure in Kepahiang: Insights from Magnetotelluric, Gravity, and Remote Sensing Techniques

This research was conducted to determine the structure and depth of the reservoir using remote sensing as an initial survey to assess the geological alignment direction, employing ALOS PALSAR radar imagery. Subsequently, further surveys were conducted using the magnetotelluric and gravity methods to analyze the structure and depth of the geothermal reservoir. The magnetotelluric data were processed using Phoenix software, where the data was transformed from the time domain to the frequency domain using Fourier transformation, and processed to obtain apparent resistivity and phase. The MT data was integrated with gravity data, and the gravity data underwent standard correction procedures to obtain the Complete Bouguer Anomaly (CBA) map. Two-dimensional (2D) inversion using the NLCG algorithm and 2D forward modeling of the gravity data were performed. The dominant alignment pattern obtained was northwest-southeast, with an orientation of 320° NW or 140° SE. Based on the results of geological alignment, a profile is produced that is perpendicular to the straightness. The results from the 2D inversion and gravity forward modeling indicated that the geothermal reservoir is likely located beneath the caprock at an estimated depth of approximately 1800 m, with resistivity values ranging from 32 to 256 Ohm-m and a density value of 2.6 gr/cc.

Regional Gravity Model of Greece Based on Satellite, Marine and Terrestrial Data

Greece is a country structured by land, several islands and sea. A regional gravity model of such a country demands the involvement of several types of gravity data in order to cover all its territory. In this paper, we present the development of a regional combined gravity model of Greece and its surrounding area, by integrating terrestrial, marine (shipborne and altimetry-derived gravity data) and satellite data (GOCE and GRACE data). These kinds of data, especially the terrestrial and marine ones, have passed quality and validation control since they were collected from different organizations, which means that they probably have been acquired and processed with different parameters and formulas. Following that, their integration was accomplished with the application of the least-squares collocation (LSC). Therefore, a newly combined regional gravity model of Greece and its surrounding areas has been developed. This gravity model can be valuable for regional geological and geophysical studies of Greece, since it provides homogeneously the distribution of Complete Bouguer anomaly (CBA) all over Greece, with updated gravity data and in good agreement with the initial gravity datasets that have been used.

Accuracy assessment of the SRTM2gravity high-resolution topographic gravity model in geoid computation

The accuracy of the SRTM2gravity high-resolution topographic gravity model is tested in this study. Complete Bouguer anomaly datasets calculated with classical formula in planar approximation and using the SRTM2gravity model in spherical approximation were compared in the study area. Two geoid models computed using free-air anomalies, which were restored from each Bouguer anomaly datasets, were compared to each other and they were validated at GPS/leveling points. In the mountainous part of the area, two geoid models differ by up to 4 cm. Following GPS/leveling validations, the geoid models provided nearly the same accuracy (∼4.2 cm). In conclusion, the accuracy of the SRTM2gravity model data was found sufficient to use in gravity reduction and it is recommended as a ready-to-use product in the area for gravity interpolation/gridding and geoid determination purposes.

Identification of Geological Structure Based on Gravity Method in Tangkuban Parahu Volcano, Bandung, Indonesia

Tangkuban Parahu Volcano, located in Cikahuripan, Lembang, West Bandung Regency, West Java, Indonesia, has a geothermal potential. However, this potential is accompanied by geohazard risks, one of which is a volcanic eruption that can interfere with the development of geothermal potential. On February 12, 2022, there was a gust of volcanic gas from Ratu Crater, indicating an increase in volcanic activity after an eruption in 2019. Based on the geological map of Tangkuban Parahu/Sunda Volcano Complex, it is estimated that there is a fault structure in a northwest-southeast direction, where if a volcanic eruption occurs, it will cause greater deformation because it cuts through Ratu Crater. Further studies with geophysical methods are needed to estimate the fault structure. The study of the subsurface geological structure of Tangkuban Parahu Volcano was carried out using the gravity method by studying variations in the gravitational field on the earth’s surface to determine differences in rock density. The Complete Bouguer Anomaly (CBA) value from the gravity method at Tangkuban Parahu Volcano shows 68 – 73 mGal, and residual anomaly values ranged from -0.95 to 0.67 mGal. The negative residual anomaly value between -0.95 to 0 mGal shows the weak zone due to volcanism in the crater. On the other hand, high residual anomaly values ranging from 0 to 0.67 mGal are interpreted as the influence of Lava 1 Tangkuban Parahu (Tl1). Analysis using First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) shows a fault structure trending Northwest – Southeast, which can be a way out of the accumulation of high-pressure water vapor due to volcanic activity.