Gravity Survey of King Fahd University of Petroleum and Minerals Dammam Dome, Saudi Arabia

The study area is a part of Dammam Dome that is situated at King Fahd University of Petroleum & Minerals (KFUPM) campus, Dhahran, Kingdom of Saudi Arabia. The gravity survey was conducted as a pilot case study to explore part of Dammam Dome in greater detail. Gravity data were collected solely during night hours due to low noise levels. A significant part of the survey was conducted during the summer holiday period, , when there was no student are on campus. A total of 235 gravity measurements were made using a Scintrex CG5 gravitometer, while a Trimble R10+ differential GPS (DGPS) was used to measure the stations’ location and elevation with the highest accuracy. All gravity data were reduced using several algorithms, and their outcomes were cross-compared. The Complete Bouguer anomaly map for the campus was then generated. Several enhancement filters including edged detection and shallow to deeper source separation were applied. Data were inverted, and 2.5D and 3D models were created to image the subsurface conditions. The main purpose of this study is to better understand the subsurface geology, tectonic settings of the Dammam Dome by applying the high-resolution gravity method before carrying out any comprehensive geophysical (seismic) 3D survey.

New Bouguer Anomaly Map for the Territory of the Slovenia

The existing Bouguer anomaly map, which covers the territory of the Republic of Slovenia is a few decades old. Since then, quite a few new gravimetric measurements (data) for the territory of Slovenia as well as high quality digital terrain models that are needed for creating such a map have been made available. The methodology and standards for creating gravity anomaly maps are also changing. Thus, the national Bouguer anomaly map was updated. There were some gross errors detected in the set of old gravimetric data. Additionally, the influence of new updated gravimetric data was analyzed. The comparison of the various maps and the analysis of the influence of input gravimetric data indicates that the new gravimetric data of Slovenia has a significant influence on the creation of the gravimetric anomaly maps for Slovenia (even over 30 mGals at some points).

Analysis of gravity anomaly and seismicity in Bali region

This study aims to determine the value of the gravity anomaly in the Bali region, identify the fault structure in the Bali region using gravity interpretation and analyze the relationship between gravity anomaly and seismicity in the Bali region. The data used is secondary data, namely satellite gravity anomaly data obtained from the topex website and earthquake data obtained from the Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG) catalog. Data processing in this study was done using gravity and Second Vertical Derivative (SVD) methods. We used Surfer15 software, Oasis Montaj, and the Generic Mapping Tool (GMT). The results of the complete Bouguer anomaly map show the anomalous value of the study area between 10-220 mGal, regional anomaly 40-190 mGal, and the residual anomaly between (-120)-60 mGal. Judging from the SVD contour map that has included earthquake data in the Bali region for the 2008-2020 period, the type of fault in the Seririt Fault, Tejakula Fault, and Fault around Mount Agung is a thrust fault. Judging from the value of the coefficient of determination, it shows that 99% of the seismicity value is influenced by gravity anomaly. The higher the value of the gravity anomaly, the higher the seismicity value.

2D Forward Modeling Geothermal System Gravity Data in South Solok Region, West Sumatra

Indonesia has the greatest potential for geothermal energy in the world. Geothermal has an important role as an alternative fuel because it is a renewable energy source, but its use has not been maximized. One of the areas that have the greatest potential for geothermal energy in South Solok, West Sumatra. Therefore, this study was conducted to determine the geothermal system in the South Solok area, West Sumatra by using the gravity method. The gravity data processing stage requires some software to get the CBA value(Complete Bouguer Anomaly), map contours of the CBA. Anomaly separation with the butterworth filter method, determination of residual anomaly slice points, and 2D modeling of geothermal systems. Based on modeling, the qualitative interpretation interprets the Complete Bouguer Anomaly map which is suspected as a geothermal prospect area is a low anomaly ranging from 7.9 mgal - 9.4 mgal which is marked in dark blue. Meanwhile, quantitative interpretation produces modeling of the AB and CD slicing with a total of four layers. This layer consists of clay rock as a cap rock, sandstone as a reservoir, granite as a heated rock as a heat source, and the last layer in the form of magma as a heat source. The anomaly modeling of these two sections is dominated by granite rock with a density value of 2500 kg/m3 for the AB section and 2550 kg/m3 for the CD section.

Combination of Terrestrial and Satellite Gravity Data for the Characterization of the Southwestern Coastal Region of Cameroon: Appraisal for Hydrocarbon Exploration

The southwestern coastal region of Cameroon is an area of interest because of its hydrocarbon potential (gas and oil). Terrestrial and satellite gravity data were combined and analyzed to provide a better precision in determining the structure of the study area. Firstly, the two gravity databases (in situ and satellite) have been coupled and validated using the least square collocation technique. Then, spectral analysis was applied to the combined Bouguer anomaly map to evaluate the thickness of sediments in some localities. We found that the sedimentary cover of the southwestern coastal region of Cameroon has a thickness that varies laterally from 1.68 ± 0.08 to 2.95 ± 0.15 km , especially in the western part. This result confirms that our target area is a potential site for hydrocarbon exploration. The horizontal gradient method coupled with the upward continuation at variable heights has been used to highlight several lineaments and their directions (N-S, E-W, SW-NE, and SSW-NNE). Lineaments trending in an N-S orientation are predominant. The Euler deconvolution method was also applied to the Bouguer anomaly map to determine the position, orientation, and depth of the different superficial faults of the study area. It appears that the majority of superficial faults have an N-S and SSW-NNE orientation. These directions are correlated with those previously highlighted by the maxima of horizontal gradient. The structural map could be used for a better identification of the direction of fluid flow within the subsurface or to update the geological map of our study area.

3D Gravity modeling of the volcanic island of Surtsey, Iceland

<p>The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones.  Constraints on the subsurface structure of Surtsey achieved mainly based on the documented evolution during eruption and from drill cores in 1979 and in the ICDP-supported SUSTAIN drilling expedition in 2017(an inclined hole, directed 35° from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019). </p><p>We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme.  Detailed gravity data were obtained on Surtsey in July 2014 with a gravity station spacing of ~100 m. Density measurements for the seafloor sedimentary and tephra samples of the surface were carried out using the ASTM1 protocol. By comparing the results with specific gravity measurements of cores from drillhole in 2017, a density contrast of about 200 kg m<sup>-3</sup> was found between the lapilli tuffs of the diatreme and the seafloor sediments.  Our approach is to divide the island into four main units of distinct density: (1) tuffs above sea level, (2) tuffs below sea level, (3) lavas above sea level, and (4) a lava delta below sea level, composed of breccias over which the lava advanced during the effusive eruption.  The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores. </p><p>A complete Bouguer anomaly map is obtained by calculating a total terrain correction by applying the Nagy formula to dense DEMs (5 m spacing out to 1.2 km from station, 200 m spacing between 1.2 km and 50 km) of both island topography and ocean bathymetry.  Through the application of both forward and inverse modeling, using the GM-SYS 3D software, the results provide a 3-D model of the island itself, as well as constraints on diatreme shape and depth.</p>

Tectonic insight and 3-D modelling of the Lusi (Java, Indonesia) mud edifice through gravity analyses

SUMMARY Lusi is a sediment-hosted hydrothermal system located near Sidoarjo in Central Java, Indonesia, and has erupted continuously since May 2006. This mud eruption extends over a surface of ∼7 km2, and is framed by high containment dams. The present study investigates the geometry of the subsurface structures using a detailed gravimetric model to visualize in 3-D the Lusi system and surrounding lithologies. The obtained residual Bouguer anomaly map, simulated through geostatistical interpolation methods, supports the results of previous deformation studies. The negative gravity anomaly zones identified at Lusi are interpreted as fractured areas through which fluids can ascend towards the surface. A 3-D detailed geological model of the area was constructed with Geomodeller™ to highlight the main features. This model relies on the structures’ density contrasts, the interpreted residual Bouguer anomaly map, and geological data from previous authors. 3-D algorithms were used to calculate the gravity response of the model and validate it by inverse methods. The final output is a gravity constrained 3-D geological model of the Lusi mud edifice. These results provide essential details on the Lusi subsurface and may be useful for possible future geothermal resource exploitation and for the risk mitigation plans related to the maintenance of the man-made framing embankment.

Caracterização Estrutural da Região Central do Graben do Cupe, Bacia Sedimentar de Pernambuco: Implicações para o Padrão Atual da Rede de Drenagem

A área de estudo está inserida no contexto geológico do Graben do Cupe, região de borda da Bacia Sedimentar de Pernambuco (BPE) com o embasamento cristalino adjacente. O Graben do Cupe é considerado um importante depocentro da região onshore dessa bacia e sua origem está ligada à abertura do Oceano Atlântico Sul. A partir da integração de dados gravimétricos, dados altimétricos obtidos por LIDAR e dados de campo, foi possível realizar uma caracterização estrutural dos principais lineamentos gravimétricos e topográficos que cortam a região central do Graben do Cupe. O mapa de anomalia bouguer residual revelou que o arcabouço estrutural mais profundo da BPE é representado por falhas normais de direção NE-SW, bem como falhas transcorrentes sinistrais, de direção NW-SE e dextrais ENE-WSW. A mesma orientação de lineamentos topográficos foi obtida através da interpretação dos dados altimétricos. Os rios inseridos na área de estudo seguem a mesma orientação dos lineamentos topográficos e gravimétricos, NW-SE e NE-SW. O mapeamento estrutural revelou que os lineamentos gravimétricos e topográficos estão associados à direção da foliação NE-SW, presente no embasamento adjacente a bacia, e às falhas originadas durante a fase rifte da BPE; A) NE-SW e NNE-SSW caracterizadas como falhas normais e B) NW-SE que corresponde a falhas oblíquas. As estruturas mais profundas tanto do embasamento, quanto as estruturas rifte que compartimentam o Graben do Cupe foram responsáveis por controlar a evolução quaternária da paisagem, o que provocou a captura da drenagem de alguns cursos fluviais, e o significante condicionamento tectônico dos vales fluviais. Structural Characterization of the Central Region of the Graben Cupe, Pernambuco Sedimentary Basin: Implications for the Current Pattern of the Drainage Network A B S T R A C TThe study area is inserted in the geological settings of the Cupe Graben, which is located in the border region of the Pernambuco Basin with the adjacent crystalline basement. The Cupe Graben is considered an important depocenter in the onshore region of this basin and its origin is linked to the opening of the South Atlantic Ocean. From the integration of gravimetric data, altimetric data obtained by LIDAR and field data, it was possible to carry out a structural characterization of the main gravimetric and topographic lineaments that cut the central region of Cupe Graben. The residual bouguer anomaly map revealed that the deep structural framework of the BPE is represented by normal faults NE-SW and NNE-SSW and sinistral strike slip faults NW-SE. The same orientation of topographic lineaments was obtained through the interpretation of the topographic lineaments. The rivers inserted in the study area have the same orientation as the topographic and gravimetric lineaments, NW-SE and NE-SW. The structural mapping revealed that the gravimetric and topographic lineaments are related to foliation in the adjacent basement NE-SW, and the faults originated during the BPE rift phase; A) NE-SW and NNE-SSW characterized as normal faults and B) NW-SE which corresponds to oblique faults. The deeper structures of both the basement and the rift structures that constraint the Cupe Graben were responsible for controlling the quaternary evolution of the landscape, which caused the capture of the drainage of some rivers, and the strong conditioning of the drainage network.Keywords: Cupe Graben, Pernambuco Basin, structural geology, river capture.

The Bouguer Anomaly Map of Iraq According to a New Local Theoretical Gravity Equation and Its Geological Importance

Four hundred and seventy eight gravity base stations in Iraq were used to obtain a new local theoretical gravity equation. The obtained equation was used to construct a Bouguer anomaly map of Iraq depending on the available gravity base stations. This map was compared with the Bouguer map constructed for the same stations using the international formula (1930). Good similarity in shapes and locations of the anomaly were observed, while the gravity anomaly values in the new map were increased by about 30 mGal. The eastern zero gravity contour line of the new obtained gravity map coincides with the western boundary of the tectonic Mesopotamian zone, while the main negative gravity values coincide with the Mesopotamian area, which contains most oil fields in eastern Iraq. All negative gravity anomaly areas coincide with the deepest basement rocks (the sedimentary basins) in Iraq. The obtained results are very valuable in geological applications.