Subsurface Structural Identification and Seismicity Correlation in West Java Using EMAG2 Geomagnetic Data

The research area "Y" is an area of gold mineralization with low sulfidation epithermal type deposit. The existence of this type of mineralization on the path marked by the presence of mineral deposits, which form the quartz veined below the surface of the deposited within the structure of the fault. In this study, analysis of gravity data using derivatives analysis, i.e. First Horizontal Derivative (FHD) to determine the boundary fault structure and Second Vertical Derivative (SVD) to determine the type of fault. The existence of the fault structure integrated with subsurface modeling results in two-dimensional and three-dimensional. The results showed three line slice made in the area of research, identified structure of down faults (normal) trending northeast - south on slice 1 with an estimated dip (slope) is 22° and expected of strike on this fault is N 158° W and thrust fault structure trending northwest - south on slice 2 also slice 3 with an estimated dip (slope) is 22° and expected of strike on this fault is N 158° E. The results of the modeling of two-dimensional and three-dimensional show fracture structure is at the density of 2 g/cc – 2,67 g/cc in the depth of around 100 m - 250 m that consists of sedimentary rocks (clay and sandstone) with a density of 2,2 g/cc – 2,3 g/cc at the age of Tertiary Pliocene, tuff rock with a density of 2,4 g/cc – 2,5 g/cc at the age of Early Miocene and bedrock (basement) in andesite form with a density of 2,67 g/cc.

Oil field research in regional Banyuasin “HUF” , South Sumatra have been done by the gravity data with objective of knowing fault structure based on analysis of hydrocarbon SVD and knows hollow structure based on the 3D model of the Bouguer Anomaly and Residual Anomaly. Study areas had Bouguer Anomaly between 13 mgal up to 33 mgal to the interval 1 mgal, where the value of Bouguer Anomaly high have a range value 26 mgal up to 33 mgal which is in the direction of west. While the low value of Bouguer Anomaly have a range value 13 mgal to 20 mgal that is in the east. To knew the existence of structure fault, filtering Second Vertical Derivative (SVD) on a Bouguer Anomaly, Regional and Residua mapl.Pattern of structure fault indicated the contours of a zero value and between the high and low contours. From the results of the analysis SVD Complete Bouguer Anomaly and SVD Residual Anomaly there were 4 (four) fault, while from SVD Regional Anomaly there are 3 (three) fault. 3D modeling the Residual Anomaly were conducted to prove the existence of the fault SVD analyzed based on the results of the analysis and to know the hydrocarbon basin. Based on the results of the inversion of 3D the Residual Anomaly, basin was found in the depth of 1500 m – 3000 m with a value of the density ranges from 2.24 gram/cc until 2.32 gram/cc which identified as sandstone basin.

This study investigates the mineral resource potential of the Ado-Ekiti and Ilesa regions in southwestern Nigeria using aeromagnetic data. These regions, located within the Precambrian Basement Complex and schist belts of Nigeria, are known for hosting significant mineral deposits, including gold, iron ore, and rare earth elements. However, limited geophysical exploration has constrained the full realization of their mineral potential. To address this, aeromagnetic data from sheets 243 (Ilesa) and 244 (Ado-Ekiti) were obtained from the Nigerian Geological Survey Agency and processed using advanced enhancement techniques to delineate geological structures and identify zones of mineralization. The study employed a suite of edge-detection filters, including Reduction to the Pole (RTP), Analytic Signal Amplitude (ASA), First Vertical Derivative (1VD), Tilt Derivative (TDR), and Total Horizontal Gradient (THG), to enhance the interpretation of magnetic anomalies. These filters improved the resolution of shallow and deep-seated features such as faults, shear zones, lithological boundaries, and dykes. Magnetic anomalies were classified into three litho-magnetic domains, corresponding to Older Granites and quartzites, undifferentiated metasediments, and mixed basement/metasedimentary sequences. Results reveal those high magnetic anomalies (65–251 nT) in areas like Ilesa and Osogbo are linked to magnetite-rich granitic and metamorphic rocks, indicative of iron ore and gold mineralization. Conversely, low anomalies (-12 to -174 nT) in regions such as Ifewara and Oriade correspond to quartzite and schist formations, potentially reflecting hydrothermal alteration zones or non-magnetic mineralization such as rare earth elements or hydrocarbons. Lineament analysis highlighted dominant NE–SW and N–S fault systems and NNW–SSE trending dykes, which are structurally significant for mineral deposition. The integration of aeromagnetic data with regional geological maps demonstrated a strong correlation between magnetic signatures and known lithological units. The methodology adopted allowed for the identification of both exposed and concealed mineral-bearing structures, providing a valuable tool for resource targeting....

Coal seam fire and coal mine fire as well as fire in coal waste or storage piles are worldwide general phenomenon and pose a great threat to the national economy, environment, ecology and health of peoples living in its proximity. In 17th century the coal mining in India first started in Raniganj coalfield in an ill- planned way and some planned mining started in an about 1820. In early days, the collieries were owned by several small companies and owners. In 1971, the Indian coal industry was nationalized under Coal India (CIL) and Bharat Coking Coal Limited (BCCL) was formed as a subsidiary of CIL. The haphazard coal mining without suitable mine planning pose several paramount threats with environmental hazards. At present it is spread over more than 70 areas. The mapping and understanding of hidden subsurface coal fire is a challenging task. In view of this, the present study was attempted for Coal fire mapping and detection of previously burnt coal fire regions in East Basuria colliery, a part of the Jharia coal field, India. Magnetic and Self Potential (SP) methods of geophysical investigation have been used for coal fire mapping over parts of Jharia Coalfield, India mainly due to cost-effectiveness with good accuracy and faster data acquisition. SP study works based on redox potential generated by oxidation of coal and also on Thomson potential due to temperature gradient. Whereas, magnetic study allows to map the previously burned, currently burning and unburned locations based on the magnetic properties of the materials and their changes with temperatures above or below Curie temperature. SP data have been analysed using Particle Swarm Optimization (PSO) technique. Magnetic data have been corrected for diurnal variation followed by correction using reduced to magnetic pole (RTP). The corrected magnetic data further, enhanced using north-south and east-west horizontal derivatives, first vertical derivative, second vertical derivative, Total horizontal derivative, Analytical signal, Tilt Derivative and downward continuation techniques. Radially averaged power spectrum (RAPS) of magnetic data has been calculated to estimate the average depth to the top of different layers. Different sets of 3D Euler’s depth solutions have been estimated separately for each various source geometry (SI = 0, 0.5, 1.0, 1.5, 2, 2.5 and 3) to understand the possible source geometry of complex fire activities. PSO inversion of SP data reveals that the depth of the coal fire extends between 10 and 12 m below the surface. The study based on SP method over East Basuria reveals that the geometry of subsurface coal combustion is possibly similar to the inclined sheet with relatively large horizontal extension. The large variations in inclination angles of the causative sources may possibly indicate complex nature of fire propagation along different inclined fractured planes which are generated in multiphase coal seam combustion. It is observed that the total magnetic field intensity anomaly of the area varies approximately from 44,850 to 47,460 nT and the residual magnetic anomaly varies approximately from −1323 to 1253 nT. The range of the magnetic anomaly after RTP is approximately 1050–1450 nT. Twelve low (L1–L12) and nine high (H1–H9) RTP magnetic anomalies have been delineated from RTP of East Basuria Colliery for 2012. The average depth to the top of different layers estimated using radially averaged power spectrum (RAPS) over East Basuria colliery are (i) 10 m, (ii) 18 m and (iii) 38 m for 2012. It is observed that the average depth of the estimated Euler’s solution for different SI is varies from 10 to 26 m for 2012. Possible fire affected, non-fire and possible baked and cool areas have been delineated as (i) 21%, (ii) 36%, (iii) 42% for the years 2012 based on RTP anomaly distribution over East Basuria colliery. The results prove the efficacy of the SP and magnetic methods for characterization of causative sources associated with coal fires over East Basuria colliery, Jharia coalfield, India.

The research aims to delineate the groundwater basin in Bandar Lampung from gravity anomaly. Field data acquisition was carried out at 403 points with a spacing of 2-3 km, covering the Bandar Lampung and surrounding areas. Data processing through gravity data corrections, namely drift, tide, Free Air, Bouguer and Terrain using Geosoft Oasis Montaj 8.3. The Bouguer density used is 2.67 gr/cm3. For the anomaly separation, spectrum analysis and regional and residual anomaly separation were carried out, whereas 2D modeling was carried out by forward modeling. This basin boundary analysis is based on gravity residual anomaly patterns, gravity Second Vertical Derivative (SVD) analysis, and 2D gravity modeling. There are two low residual anomaly patterns (-22 to -5 mGal), where the boundaries of the basin can be clearly delineated from SVD analysis. This 2D model shows layers with a density of 2.3 gr/cm3 which are the Young Volcano Formation (Qhv) and the Lampung Formation (QTl) which have depths of up to 1.0-1.5 km. This Groundwater Basin correlates well with the hydrological pattern with a water discharge of 5 to 100 l/sec.

This study uses the gravity method to assess the characteristics of the Manna segment fault, a part of the Sumatran fault. This research aims to contribute to the existing knowledge by providing additional insights into the fault's characteristics, which is essential for future disaster mitigation efforts. The Manna segment fault is geographically situated between coordinates 4.4⁰S - 3.9⁰ S and 102.7⁰ E – 103.2⁰ E, making this area prone to earthquake hazards. The gravity anomaly data, including free air and topography, were collected from 62,501 data points. The Simple Bouguer Anomaly (SBA) values obtained ranged from 25 mGal to 95 mGal. By utilizing the Second Vertical Derivative (SVD) method and dividing the study area into three regions with multiple sections, the analysis revealed that the minimum and maximum SVD values were relatively similar. This suggests that the Manna fault can be classified as a strike-slip fault, with SVD values ranging from Elkins-20 mGal to 6 mGal. The study identified branches of the main fault in regions 2 and 3 based on the SVD map. Overall, this study enhances our understanding of the Manna segment fault, providing valuable insights into its characteristics and contributing to future disaster mitigation efforts.

A ground gravity survey was conducted over the Blawan-Ijen geothermal area covering about 176 km2 area. A total of 72 stations were measured with 1.0 – 1.5 km spacing. The data obtained were then processed using several corrections for gravity data to get Complete Bouguer Anomaly (CBA). The gravity method was chosen because of the ability to detect geological structures corresponding to the rocks density of the field study. Two types of gravity technique, First Horizontal Derivative (FHD) and Euler Deconvolution (ED), have become widely used to interpret the structure condition. FHD technique delineates a geological boundary of different density body while ED technique estimates a source location and depth of structures. Furthermore, 3-D inversion of magetotelluric data result was also used as a reference to support 2-D gravity forward modeling. The main structure which probably controlled the emergence of Blawan-Ijen hotspring is indicated by maximum FHD value at the northern part area. Moreover, the ED result shows the depth of structures in Blawan-Ijen geothermal area is mostly about 250 – 1000 meters.

Tectonic structures of SW margin of Gondwana from gravity and magnetic anomalies of the Río de la Plata area and their correlation with the Beattie magnetic Anomaly in South Africa

The transformation of magnetic anomalies to magnetic potential or pseudo-gravity simplifies the complexities of magnetic anomaly interpretation. We present new pseudo-gravity maps, derived from EMAG2v3 data, for the South Atlantic Ocean and adjacent continent to reveal insights into crust and lithosphere composition.The pseudo-gravity transformation of the full-field magnetic anomaly consists of three steps: (i) reduction to the pole (RTP); (ii) integration to determine magnetic potential; and (iii) scaling to determine the pseudo-gravity, assuming a constant ratio of density contrast to magnetization. This transformation produces a gravity-like anomaly that would be observed if the magnetization were replaced by a density distribution of proportional magnitude. We use magnetic data from the public domain EMAG2 v3 as the primary input. The South Atlantic region was divided into 90 tiles of 5º to account for regional variations in magnetic inclination and declination. An important assumption for the transformation is that the magnetization is induced. The pseudo-gravity mapping shows large amplitude positive anomalies consistent with the assumption of induced magnetization; negative anomalies identify areas of remnant magnetization. In the oceanic domain, alternating positive and negative anomalies reflect magnetic reversals and are not an artifact.On the South American plate, the Rio-Grande-Rise exhibits three distinct high positive pseudo-gravity anomalies, reflecting thick magmatic crust. The São-Paulo-Plateau in the Santos Basin, Florianópolis-Ridge and Torres-High also show high positive anomalies. The Campos Basin has lower-amplitude positive anomalies, suggesting localized magmatic crust. In the continents, high-amplitude positive anomalies correlate with magmatic intrusion. The high positive pseudo-gravity anomalies form an NW-SE arc from magmatic material in the Paraná Basin to the São-Paulo-Plateau, continuing through the Florianópolis-Ridge and Rio-Grande-Rise.Strong positive anomalies along the Namíbia-Ridge, Walvis-Ridge, and southwestern African margin form a "7"-shaped uniform anomaly, corresponding to magmatic crust. In contrast, the oceanic crust offshore Orange Basin shows a north-south region of negative anomalies. No significant anomalies are seen in the Tristan-Gough Guyot Province (nor are they seen on the Vitória-Trindade or Tristan-Gough Guyot Province hot-spot tracks).A comparison of the pseudo-gravity map with crustal thickness from gravity inversion shows that many large, high-amplitude positive pseudo-gravity anomalies in the oceanic domain correlate strongly with anomalously thick crust (>12.5 km thickness) on the Rio-Grande-Rise, São-Paulo-Plateau, Florianópolis-Ridge, Namíbia-Ridge and Walvis-Ridge. Plate reconstruction of pseudo-gravity anomalies and crustal thickness suggest that the Namíbia-Ridge and western Florianópolis-Ridge, both with thick magmatic crust, have a common origin at approximately 110 Ma but were later separated by the Florianópolis-Fracture-Zone. The spatial relationship of observed high positive pseudo-gravity anomalies on magmatically intruded crust in the South American and African continents, the hybrid or magmatic crust on their rifted margins and thickened magmatic crust within the South Atlantic shows the major role of mantle inheritance in their origin.

Edge detection in potential fields with the normalized total horizontal derivative

    Magnetic anomalies commonly contain anomalies generated by crustal rocks that have variable mineral compositions and natural remanent magnetizations. Understanding the magnetic susceptibility, remanent magnetization, magnetization direction, and distribution is important for studying the spatial location, formation, and evolution of underground rocks. However, superposition of magnetic anomalies leads to nonnegligible errors of inversion and interpretation. To overcome the interpretation problems caused by source interference, it is necessary for the target magnetic anomaly to be extracted from the observed magnetic anomaly data. Different methods have been developed to separate the magnetic anomalies of different sources using the spectral differences of regional and residual anomalies. Such methods, which include matched filtering, Wiener filtering, and wavelet analysis, have been successfully applied to solve many geological problems. However, these methods cannot extract the anomalies caused by the interference of sources at similar depths because the spectra of the target and residual magnetic anomalies are similar. Effective techniques to obtain additional magnetic information regarding the distribution of rocks at different layers and with different magnetization directions remain lacking.    Unlike existing regional-residual separation methods used for separating superimposed magnetic anomalies caused by sources with a large depth separation, this study focuses on magnetic anomalies generated by variability of the magnetic parameters and source interference with and without depth differences. We propose a new and useful method for extracting a target magnetic anomaly from an observed magnetic anomaly field. An optimization scheme is proposed for approximating the low-rank component of an observed magnetic anomaly field on the basis of low-rank theory. The magnetic dipole layout is added as a constraint based on the assumed source location. The optimal magnetizations of the magnetic dipoles are then obtained to minimize the objective function. The sum of the magnetic anomalies generated by the magnetic dipoles is calculated as the target magnetic anomaly. The synthetic and field data experiments indicate that the proposed method can accurately and robustly recover target magnetic anomalies. In the field data experiments, the magnetization information of the various isolated sources is derived via 3D fuzzy C-means inversion using the extracted magnetic anomalies. The results show that the proposed method can extract the geometric and physical information of each target magnetic source, even when the observed magnetic anomaly field is generated by various superimposed sources with target source interference at similar depths. The proposed method has the potential for dealing with the separation problems of potential field data with different scales, including the separation of the geomagnetic core field and the lithospheric magnetic field as well as the extraction of target magnetic anomalies from satellite magnetic measurements. Therefore, this approach could be of great importance for geological investigations and mineral exploration.

Interpretation of the subsurface tectonic setting of the Natrun Basin, north Western Desert, Egypt using Satellite Bouguer gravity and magnetic data

An approach for estimating the magnetization direction of magnetic anomalies

The exposed granite gneissic complex to the west of Cuddapah basin in Eastern Dharwar Craton (EDC) is studied to understand the magnetic character of various plutons in this region with more emphasis on a part of Closepet Granite (CG). The NW–SE trending plutons in this region show gradual decrease in magnetic intensities from southwest to northeast; CG in the southwest corner of the study area have high mafic content, and there onwards show a depletion in mantle enrichment towards NE. Parts of the CG namely, the main mass and northern intrusions separated by a gap zone are differentiated based on magnetic character deduced by processing the aeromagnetic data. Reduced to the pole (RTP) and its upward continued maps revealed NNW trending eastward convex anomaly highs inferring the magnetic nature of CG due to Porphyritic Monzogranite (PMG). Gap zone is identified to be structurally significant, bounded by deep ENE faults and inferred to be associated with PMG at relatively deeper levels. 2.5D modelling of magnetic anomaly profile substantiated our qualitative analysis of magnetic anomalies over CG, inferring magnetic and non-magnetic units of CG. Known shear zones running north–south are identified with a few inferred shears revealed from magnetic data interpretation within CG.

A new method is introduced here to interpret the magnetic anomalies with special reference to vertical magnetic anomalies of a horizontal circular cylinder. The parameters of the cylinder are found to be related toV, ∂V/∂x and∂V/∂z at the origin of the cylinder. HereV is the observed anomaly,∂V/∂x and∂V/∂z are its horizontal and vertical derivatives respectively. The origin may be located working out an equality,viz.,3(∂V/∂z) 2=2V∂2V/∂z2 which is true only at the origin. Thus, once the cylinder is located,V, ∂V/∂x and∂V/∂z at its origin can be determined and hence its parameters. The procedure is illustrated with a theoretical example.