Causative Sources Research Articles

Delineation of the Subsurface Structures in the Central Sumatra Basin (Indonesia) through Bouguer Gravity Data

This study presents the delineation of the boundaries of the subsurface structures located in the eastern part of the central Sumatra basin using Bouguer gravity data. The existence of the high gravity anomalies in the eastern part displayed in this sedimentary basin takes attention. Therefore, investigation of the reason for these high anomalies is required for the region. To this end, gravity anomalies have been processed by advanced potential field methods such as the power spectrum analysis method and tilt method. The average depths of the deep and shallow causative sources have been calculated as 23.71 km and 1.61 km, respectively. Furthermore, the boundaries of the causative sources have been determined utilizing the tilt method. The tilt map has shown that the reason for these high anomalies could be the bedrock composed of high-density material rising upwards, considering the tectonic background of the region. This study has determined that this high structure is in the form of a triple structure and that its upper depths are approximately 5.8 km, 11.30 km, and 12.8 km from north to south, respectively. As a result, it could be said that such sources with deep roots could be prospective for hydrocarbon maturation.

The correlation between the active/buried faults and aeromagnetic data in inner and inner-east Anatolia, Turkey

The paper focuses on investigating the active/buried faults in inner and inner-east Anatolia, Turkey based on aeromagnetic data and comparison with the active fault map. This region includes the major tectonic units of Turkey and the largest basins of Turkey (Tuzg.lü Basin (TB) and Sivas Basin (SB)). Thus, the region deserves a detail investigation to delineate the lineaments of the active/buried fault system or the causative sources located in the upper crust. To this end, the region has been divided into two parts as region-1 and 2 including TB and SB, respectively. In this context, the geophysical data processing techniques including power spectrum analysis, high‑pass filter, and second vertical derivative method (SVD) have been applied to the aeromagnetic data of the both regions. Firstly, by utilizing power spectrum analysis, the average depths of the deep and shallow causative sources in the region-1 have been calculated as 11.37 km and 5.01 km whereas those depths are 8.5 km and 3.24 km for region-2. Afterwards, to enhance the responses of the residual anomalies, the high‑pass filter and the SVD method have been applied to the data. Hereby, these potential lineaments produced from the SVD map have been compared with the active fault map to delineate the uncovering buried faults and their lineaments in the region. Contrary to the discussion in the literature, this study revealed for the first time that the Tuzgölü fault zone located in the eastern part of lake does not merge with the Ecemis fault (EF) zone. Furthermore, the study has shown that this fault zone extended from Kayseri city to Sivas city does not junction with North Anatolian Fault Zone in the north, as well.

Food-Pollen Cross-Reactivity and its Molecular Diagnosis in China.

Plant-derived foods are one of the most common causative sources of food allergy in China, with a significant relationship to pollinosis. This review aims to provide a comprehensive overview of this food-pollen allergy syndrome and its molecular allergen diagnosis to better understand the cross-reactive basis. Food-pollen cross-reactivity has been mainly reported in Northern China, Artemisia pollen is the major related inhalant source, followed by tree pollen (Betula), while grass pollen plays a minor role. Pollen allergy is relatively low in Southern China, with allergies to grass pollen being more important than weed and tree pollens. Rosaceae fruits and legume seeds stand out as major related allergenic foods. Non-specific lipid transfer protein (nsLTP) has been found to be the most clinically relevant cross-reacting allergenic component, able to induce severe reactions. PR-10, profilin, defensin, chitinase, and gibberellin-regulated proteins are other important cross-reactive allergen molecules. Artemisia pollen can induce allergenic cross-reactions with a wide range of plant-derived foods in China, and spring tree pollens (Betula) are also important. nsLTP found in both pollen and plant-derived food is considered the most significant allergen in food pollen cross-reactivity. Component-resolved diagnosis with potential allergenic proteins is recommended to improve diagnostic accuracy and predict the potential risk of causing allergic symptoms.

Unravelling seismogenesis and characterizing the unique features of two significant felt earthquakes (M > 4.0) of 2020 in the southwestern parts of the Delhi region

Two significant earthquakes (M4.6 and 4.2) occurred close to a NE–SW-trending lineament in the southwestern part of the Delhi NCR (National Capital Region) within a short time span of about 5 months in 2020. These events were located to the north of the Alwar district in Rajasthan and generated a significant ground shaking in and around Delhi. In the present study, we tried to understand a causal relationship between the events and a nearby source in the region, geologically demarcated as the lineament. We analyzed the broadband waveform data from 26 seismic stations that recorded the recent events of 03 July 2020 (M4.6) and 17 December 2020 (M4.2). Typically, the epicentral area has been devoid of significant earthquakes since the past six decades; however, a few minor events (M < 4.0) have been recorded till date. Analysis of the earthquake database for two decades (2000–2022) revealed low seismicity (nearly quiescent-like situation) in ∼100 sq km area around the epicentral zone, unlike considerable seismicity along faults/lineaments close to the Delhi region. The full-waveform inversion analyses of the events indicate normal faulting with a minor strike–slip components. The source parameters, viz., source radius, stress drop, and seismic moment, were estimated to be 6 km, 166 bars, and 8.28E+15 Nm, respectively, for the 03 July 2020 event and 4 km, 138 bars, and 2.29E+15 Nm, respectively, for the 17 December 2020 event. The causative source of these events is ascertained based on the stress inversion modeling that indicated a NW–SE tensile stress corroborating well with the NE–SW-trending lineament mapped in the study region. The static Coulomb stress modeling indicated that the event which occurred on 3 July 2020 had advanced the triggering process of the event in the northeast segment of the same source that occurred on 17 December 2020. We further emphasize that the aforementioned lineament probably activated due to the regional tectonics of the study area. The causative source of these events with strike 48°, dip 86°, and rake −60° is found to be in the conformity with the local tectonics and is well-supplemented by a high stress ratio (0.70 ± 0.05) and low friction coefficient (0.5).

Magnetic Structural Depth Classification Using Center for Exploration Targeting And 3D Euler Deconvolution: A Case Study of Shanga (Sheet 96) North West, Nigeria

The present study involved the use of 3D Euler deconvolution to classify the depth of occurrences of magnetic structures as explicated and elucidated by the Centre for Exploration Targeting Plug-in (CET). To achieve this aim, the residual magnetic anomaly was first reduced to the equator (RTE) to centre the anomaly peaks directly above each causative source. After that, the RTE data was imputed into the CET plug-in, which is an extension of Oasis Montaj, to delineate structures that occur within the area. A 3D Euler deconvolution map with a structural index of one (SI = 1) that identified faults, dykes, and horizontal bodies was created using the RTE data. The Euler deconvolution depths were classified for depths that are <150 m, between 150 m and 300 m, 300 m and 450 m, and > 450 m. The CET delineated structures were superimposed over the 3D Euler deconvolution map with SI = 1, and most of the CET structures coincided with the structures from the Euler deconvolution map with SI = 1. Since Euler solutions are classified based on depth, the Euler structural map was used to classify the CET delineated structures based on their depths. The Euler structural map was imported into ArcGIS version 10.8 to digitize the structures based on their corresponding depth as displayed on the 3D Euler deconvolution map of SI = 1. After digitizing the Euler map with a structural index equal to one (SI = 1) with classified depth, a new structural map was then produced depicting each structure delineated with the CET based on their respective depth.

Geodetic imaging of magma ascent through a bent and twisted dike during the Tajogaite eruption of 2021 (La Palma, Canary Islands)

On Sept. 19th, 2021, the largest historical eruption on the island of La Palma began, which had a significant scientific, social, and economic impact. The 2021 Tajogaite eruption was characterised by short precursors, lasting only 8 days. The seismicity started on Sept. 11th with a westward and upward migration of hypocenters. Permanent GNSS stations started recording deformation on Sept. 12th on the island's western side, which reached more than 15 cm just before the eruption. After the eruption onset, the ground deformation increased, reaching a maximum on Sept. 22nd and showing a nearly steady deflation trend in the following months. To better understand the dynamics of the eruption, we exploited a joint dataset of GNSS and Sentinel-1 SBAS time series along both ascending and descending orbits. To obtain the geometry of the causative source of the ground deformation, we combined the result of a preliminary non-linear inversion and the precise location of the seismicity. The resulting geometry of the source is that of a twisted dike bending eastward. We performed inverse modelling to obtain the spatiotemporal kinematics of the opening function of the dike. The forward modelling has been realised using a 3D finite-element approach considering the island's topography. Our findings reveal a close correspondence between the magmatic intrusion and pre-eruptive seismicity. The ascent of the magma occurred along two branches, and the rheology of a previously identified ductile layer strongly affected the magma propagation process. Finally, we found evidence of an early shallow deformation, which we interpret as the effect of ascending hydrothermal fluids. Our findings highlight the need for advanced modelling to understand pre-eruptive processes in basaltic volcanoes.

Seasonal variation in metals concentration associated with settled dust and their risk assessment in school children of Agra (India)

Metals associated with indoor dust are shown to be a key pollutant and resuspension of dust in critical microenvironments like schools can lead to detrimental health effects to children. The present study was carried out from December 2021 to November 2022 to examine variations in metal concentration with season and associated health risks from school dust in Agra, India. Dust samples were digested in aqua-regia followed by analysis for metals concentration by ICP-AES. Geo-accumulation (Igeo), pollution (PI), integrated pollution (IPI), and pollution load (PLI) indexes were used to determine metals contamination, Principal Component Analysis and Cluster Analysis were employed for the identification of causative sources of metals while USEPA health risk assessment models were utilized to assess the health risks in children. The results indicated that in all seasons settled dust of roadside schools of both regions accumulated higher concentrations of metals as compared to residential schools except semi-urban schools in post-monsoon season. The total metal concentration (mgkg−1) in school dust samples of Agra ranged from 62507–85037, 72477–97022, 48912–66083 to 58605–92290 in winter, summer, monsoon, and post-monsoon respectively. In all seasons, the PLI values of settled dust of all schools ranged from less than one to greater than unity which indicates pollution levels by metals. Further, Igeo values revealed that school dusts were moderately and heavily contaminated by Cd in all seasons. The assessment of health risk specifies ingestion as the main exposure route followed by dermal intake and inhalation. The Hazard Index value for all examined metals was lower than the safer limit of one while on the contrary for Pb, total cancer risk was higher the than safer limit via inhalation pathway. The findings of the study indicate that more investigations are required on potentially toxic metal contaminations in schools of Agra, especially for Pb, Cd and Cr.

PM2.5 bound polycyclic aromatic hydrocarbons in an Indian residential indoor air environment and their health risk

Polycyclic Aromatic Hydrocarbons (PAHs), a group of semi-volatile organic pollutants with 2–7 aromatic rings are emitted in association with particulates/gases from incomplete combustion. They are persistent and affect human health adversely. This is the first study wherein PM2.5 bound PAHs from 8 different indoor air pollution sources, namely dhoop (DH1, DH2), incense sticks (IS1, IS2), cigarette, mosquito coil and solid fuels ‘coal and wood’, that are widely used in South-Asian countries were studied. Their emission rates and concentration profiles were compared. Dhoop was studied for the first time and found to be emitting the highest quantity of total PAHs. FLA/(FLA + PYR) ratio rightly indicated ingredients like wood and grass as sources. However, other ratios indicated petrogenic/coal origin, while BaP/(BaP + CHR) and BaA/(BaA + CHR) ratios were not reported earlier. The highest Toxicity Equivalent Concentration and Mutagenic Equivalent Concentration were estimated for DH2 and the lowest for cigarette smoke. The maximum Inhalation Lifetime Cancer Risk equal to 1.85 × 10−05 (adults) was observed for DH2, exceeding the WHO guidelines. These inferences will help in optimizing the indoor sources’ combustion duration and formulating manmade indoor sources. They will assist in identifying high-risk indoor environments, causative sources and control mechanisms.

Comparison between Upward Continuation and Gaussian Techniques, and their Relation to the Source Depth, Case Study in Eastern Central Iraq

The IGMAS+ forward program is used to compare upward continuation and Gaussian wavelength techniques in separating residual from regional anomalies of gravity data of a synthetic model and case study area, in eastern central Iraq. The comparison indicate a certain relation between the upward continuation and the Gaussian wavelength cutoff, so it is possible to produce the same regional and residual anomaly maps using each one of them. For the study area, the Gaussian cutoff 115000 maps coincide with the upward 12km regional and residuals maps, also the Gaussian cutoff 455000 maps coincide the upward 54km.The relation between the parameters of the two techniques, in case of produce coincide maps, it may be used to obtain the depth of gravity anomaly causative sources. It is found that ratio of Gaussian wavelength cutoff parameter to the upward parameter multiplied by 1.25 equal to the average level depth below the deeper source causing the residual anomalies. The average depth of residual anomalies in the case study area found equal to 10.5 km. The basement depth in the study area were coincide with the depth values from previous studies and geologically is very acceptabile.

LA-ICP-MS U-Pb cassiterite age data of the Sadisdorf deposit link Sn-Li-(W-Cu) mineralization in the eastern Erzgebirge to the collapse of the Altenberg-Teplice Caldera

The Sadisdorf Sn-Li-(W-Cu) prospect in the eastern Erzgebirge (Germany) comprises two distinct styles of magmatic-hydrothermal mineralization, namely greisen-type mineralization at the Kupfergrube site, and stockwork-type mineralization at both the Kupfergrube and the Zinnklüfte sites. Previously, these two sites were regarded as expressions of two temporally distinct mineralization events. In this study, this temporal relation was tested by LA-ICP-MS U-Pb data obtained for 16 cassiterite samples, including samples from both sites and styles of mineralization. All 16 samples define a narrow range of ages between 315.1 ± 1.7 / 3.3 Ma and 311.0 ± 3.1 / 4.0 Ma. All ages overlap within uncertainty, suggesting that mineralization across the Sadisdorf prospect is likely related to the same magmatic-hydrothermal event.On the regional scale, the cassiterite ages suggest that Sn-Li mineralization is associated with late-stage felsic magmatism directly following the collapse (∼314–313 Ma) of the Altenberg-Teplice Caldera. The cassiterite ages also overlap with garnet U-Pb LA-ICP-MS ages of Sn-rich skarn occurrences in the western Erzgebirge (e.g., Breitenbrunn, Antonsthal and Hämmerlein). This observation provides direct evidence that greisen and skarn-hosted Sn mineralization are related to the same period of magmatism. The data indicate that the majority of Sn-mineralization in the Erzgebirge formed after 318 Ma (likely between 318 and 310 Ma), challenging previous models which invoked an older suite of granites (326–318 Ma) as causative source intrusions.

Spatial and temporal control of the volcanic activities over the distribution of sediments in the Magadi basin, Kenya Rift

High-velocity layers in basins with significant sub-basalt coverage, such as the Magadi basin, can impede geophysical imaging of potential subsurface hydrocarbon deposits. Using magnetic and gravity methods, this study examines the influence of volcano-tectonic processes and the basement on the evolution of the Magadi basin. Regional-residual separation analyses identified key structures and signatures. Lineaments and depths of the causative sources were determined using Euler deconvolution. Butterworth low-pass filters on aeromagnetic data isolated depth-varying magnetic layer responses. The study demonstrates a westward displacement of volcanic flows in the Magadi basin, originating from nearly all volcanic plugs. Depocenters near the western boundary fault are more affected by westerly movements of the volcano-tectonic flows than depocenters near the eastern boundary fault. The Rift underwent internal compartmentalization, resulting in depocenters with unique and intermittent tectonic and sedimentary occurrences. Rift segmentation led to modifications in catchment areas, which caused sudden variations in sediment flux, ultimately leading to the isolation of the depocenters. This study identifies the initial compartmentalized depocenters of Nguruman, Koora, and Forty-six. The initial Nguruman depocenter is oriented SW-NE and spans approximately 2512 sq. km with a sediment thickness range of 2000–4000 m. The presence of horsts in the southern and northern parts precludes volcaniclastics from the depocenter. Active tectonics and inversion caused the initial Nguruman depocenter to split into two halves: the northern Musenke depocenter and the southern Pakase. Euler depth analysis indicates sedimentary formations are thicker in compartmentalized depocenters in Magadi's western and southern regions than near the eastern boundary fault. The sediment thickness range in the Koora basin is approximately 1000–3000 m, while Pakase on the western flank has a sediment thickness range of 2000–3800 m.

Enhancement of Potential Field Source Boundaries Using the Hyperbolic Domain (Gudermannian Function)

Horizontal boundary identification of causative sources is an essential tool in potential field data interpretation due to the feasibility of automatically retrieving the boundary information of subsurface gravity or geomagnetic structures. Although many approaches have been proposed to address these issues, it is still a hot research topic for many researchers to derive novel methods or enhance existing techniques. We present two high-resolution edge detectors based on the Gudermannian function and the modifications of the second-order derivative of the field. The effectiveness of the newly proposed filters was initially tested on synthetic gravity anomalies and geomagnetic responses with different assumptions (2-D and 3-D; imposed and superimposed; noise-free and noise-contaminated). The obtained results verified that the two novel methods yield the capability of producing high-resolution, balanced amplitudes and accurate results for better imaging causative sources with different geometrical and geophysical properties, compared with the other nine representative edge enhancement techniques. Furthermore, the yielded results from the application of the two strategies to a real-world aeromagnetic data set measured from the Central Puget Lowland (C.P.L) of the United States and a gravity data set surveyed from the Jalal Abad area of Kerman province, Iran, with detailed comparative studies validated that the edges identified via the two methods are in good agreement with the major geological structures within the study areas and the determined lateral information using the tilt-depth, top-depth estimation method. These features make them valuable tools for solving edge detection problems.

Trace element compositions and geochronology of cassiterite from the Bushveld Large Igneous Province, South Africa

This study presents trace element compositions and ages of four representative cassiterite samples from the Zaaiplaats, Union and Rooiberg Sn fields, all spatially associated with the Bushveld Large Igneous Province (LIP), South Africa. The Zaaiplaats Sn field is endogranitic and entirely hosted within the variably-altered Bobbejaankop and Lease granites of the Lebowa Granite Suite. In contrast, the exogranitic Union and Rooiberg Sn fields occur within the Union Tin Member of the Rooiberg Group, and the Pretoria Group of the Transvaal Supergroup, respectively. Collectively, all the cassiterite samples display quasi-parallel chondrite-normalised rare earth element (REE) patterns characterised by relative enrichments in the heavy REE, and yielded ages varying within a relatively restricted interval between 2061 ± 40 Ma and 2054 ± 3 Ma. This age range compares well with those reported from the Bushveld LIP and, when combined with mineral compositions, suggests a common granitic source for cassiterites from all the Sn fields. The exogranitic Rooiberg and Union Sn fields are identified by cassiterites with Zr/Hf of ∼40, whereas the endogranitic Zaaiplaats Sn field is characterised by cassiterites enriched in most incompatible elements (e.g., Nb, Ta, Zr, Hf, In, F and B) and Zr/Hf of ∼10. These Zr/Hf ratios agree with the endogranitic and exogranitic Sn ores from other localities, but are different from the very low Zr/Hf ratios of ∼3 reported for endogranitic cassiterites associated with rare-metal granites. The Zr versus Hf discrimination diagram may therefore be useful for distinguishing the endogranitic and exogranitic origins of cassiterites and for identifying the extent of fractionation of the causative source.

Favourable IOCG and polymetallic environs in Marwar - Khetri, NW Indian Shield imprints from aerogeophysical data analysis

The analysis of aeromagnetic data reveals two significant broad oval-shaped aeromagnetic anomalies oriented in the NE-SW direction, west of Laxmangarh and east of Fatehpur. These significant anomalies identified beneath sand-alluvium-covered areas of Rajasthan's Marwar region are of a low dominance nature. These magnetic signatures are associated with gravity gradients in the regional Bouguer gravity map. Magnetic anomalies and subsurface modeling revealed that the remanence source had a high magnetic susceptibility. The ground gravity profiles across the Laxmangarh anomaly show a high gravity variation of 5 mGal/km. The integration of geochemical distribution patterns, spectrometric elemental concentrations, different ratios, and composite image maps has brought out alteration/shear zones that are favourable for mineralization. The results of selective 2D-profiles, plate modeling, and 3D-inversion modeling of these anomalies reveal that the depth of the causative source varies from 300 to 1000 m. The higher-order magnetic susceptibilities, geochemical dispersion pattern, and spectrometric ratio maps and composite images distinguished hydrothermal alteration zones characterised by potassium enrichment. The results indicate the possibility of concealed source rocks with high magnetic mineral content (magnetite, maghemite, titanomaghemite, pyrrhotite, and franklinite?) and a relatively high density. The geophysical signatures observed around Fatehpur and Laxmangarh, with high magnetic contrast, low dominance, and remanence coupled with high gravity values, as well as hydrothermal alteration zones, appear to have striking similarities with the geophysical and geochemical scenarios of some of Australia's Iron Oxide Copper-Gold (IOCG) prospects in the Gawler, Arunta, Tennant, and Mount Isa regions. Therefore, these anomalous areas may be explored for the possibilities of an IOCG or polymetallic type of mineral.

A balanced edge detector for aeromagnetic data

One of the most significant challenges in interpreting magnetic data is to mitigate the influence of the magnetization direction in the shape of the anomalies, especially when reduction to the pole fails to position them over the sources. We propose a balanced high-order filter that has low sensitivity to the direction of the resultant magnetization. We consider an edge-detector filter based on directional analytic signals of the vertically-integrated anomaly field. To ensure that anomalies from shallow and deep sources are equalized, we balance this filter with the magnitude of its two-dimensional Hilbert transform. The proposed filter is tested using aeromagnetic data from Apiaí Terrane, Southern Brazil. The enhanced map is highly correlated with the study area's NE-SW trend of geological structures. Our results highlight the importance of using the directional analytical signals, which help reduce the influence of the magnetization direction, and the balancing filters, for equalizing the signal of shallow and deep causative sources.

A review on theory, modeling, inversion, and application of self-potential in marine mineral exploration

The self-potential (SP) method is one of the passive geophysical exploration techniques, which employs measurements of naturally occurring electric potential differences on the ground surface and in boreholes or (sea-)water due to causative sources from electrochemical, electrokinetic, and thermoelectric mechanisms. SP signals are directly related to groundwater flow and (electro-)chemical gradient. There has been increasing interest in the application of SP measurements in mineral exploration, environmental surveys, and hydrogeophysical problems. This review focuses primarily on the theory concerning the causative source mechanism, numerical modeling, and inversion and interpretation of SP signals related to ore bodies and applications in mineral exploration. Three field examples focusing on seafloor sulfide deposits exploration are summarized to show the application effect of SP measurements in marine mineral exploration. This study would be helpful to investigating the use of SP surveys in ore prospecting, especially in marine environments.

Earthquake Phase Association with Graph Neural Networks

ABSTRACTSeismic phase association connects earthquake arrival-time measurements to their causative sources. Effective association must determine the number of discrete events, their location, and origin times, and it must differentiate real arrivals from measurement artifacts. The advent of deep-learning (DL) pickers, which provide high rates of picks from closely overlapping small-magnitude earthquakes, motivates revisiting the phase association problem and approaching it using the methods of DL. We have developed a graph neural network associator that simultaneously predicts both source space–time localization, and discrete source-arrival association likelihoods. The method is applicable to arbitrary geometry, time-varying seismic networks of hundreds of stations, and is robust to high rates of sources and input picks with variable noise and quality. Our Graph Earthquake Neural Interpretation Engine (GENIE) uses one graph to represent the station set and another to represent the spatial source region. GENIE learns relationships from data in this combined representation that enable it to determine robust source and source-arrival associations. We train on synthetic data, and test our method on real data from the northern California seismic network using input generated by the PhaseNet DL phase picker. We successfully re-detect ∼96% of all events M >1 reported by the U.S. Geological Survey (USGS) during 500 random days between 2000 and 2022. Over a 100-day continuous interval of processing in 2017–2018, we detect ∼4× the number of events reported by the USGS. Our new events have small-magnitude estimates below the magnitude of completeness of the USGS catalog, and are located close to the active faults and quarries in the region. Our results demonstrate that GENIE can effectively solve the association problem under complex seismic monitoring conditions.

A new approach automatic separation of the Bouguer gravity anomaly, using a new concept for 2D-semi-inversion of the sphere-shaped model

ABSTRACT The present research represents a new, fast and easy-to-apply semi-inversion technique for the direct separation of the Bouguer gravity anomaly to its corresponding depths or thicknesses of the prior known rock formations from a borehole (as a control point). As well as the possibility of tracing these formations on the profile points to the Bouguer gravity map according to their density contrasts with basement rock. The proposed method is based on the fact that the sum of the gravitational effect at a point on the Earth’s surface is equal to the sum of the subsurface gravity effects arising from the points of masses of the causal bodies along the vertical line between the Earth’s surface and the basement rocks. In this method, two sedimentary basin models were built based on the distribution of densities from a prior known borehole. Assuming that the depths of the pointed tops of these rock formations can be replaced by the centres of sphere bodies (or point masses) as causative sources of gravitational effect and by the use of a simple algorithm, it was possible to calculate the depths of the rock formations and trace them on the profile, using a new concept called the zero-offset gravity measurement. In this concept, the measuring gravity is vertically above the centre of the sphere-shaped body as it represents the causative source, and its depths are equal to the radius of the sphere body. The present method was assessed on hypothetical models and synthetic data and applied to two real data in field cases which vary in geological and lithological aspects. The first assessed location is Abu Roash Dome Area, southwest Cairo, Egypt, and the second location is the Mors Salt Dome, North Jutland, Denmark.

New Methodology in Interpretation of Aeromagnetic Anomalies over Pipe-Like Sources using Analytic Signal Ratio Approach

Concepts of signal processing like Fourier transform, filtering, power spectrum, derivatives etc., are widely used in geophysical models in exploring the Earth structures. For example, quantitative interpretation of aeromagnetic maps is based mainly on choosing an appropriate model for evaluating parameters of the causative source. For circular or elliptical anomalies caused by plug-like intrusive sources, the vertical pipe of infinite depth extent (also known as single or mono pole) is most suited. It is also more common to use analytic signal maps in interpretation. For a vertical pipe, the total magnetic intensity (TMI) anomaly is anti-symmetric at the magnetic equator and progressively becomes symmetric at the pole. Based on this property, a new methodology is developed for identifying location and depth of magnetic structures beneath. It is concluded that the analytic signal is almost symmetric for any magnetic latitude and by using both the properties of the anomaly and its analytic signal the location and depth can be evaluated. This new approach is validated by field examples. HIGHLIGHTS The theory and application of using analytic signal to determine the location and depth to the point pole is described The method is useful in locating pipe-like (vertical cylinder, kimberlite pipes) structures The shape of the magnetic anomaly changes with magnetic inclination whereas the analytic signal map is symmetric and almost circular, with its maximum centred over the top of the pipe The analytic signal is almost symmetric for any magnetic latitude and by using both the properties of the anomaly and its analytic signal, the location and depth to the top can be evaluated GRAPHICAL ABSTRACT

Interpretation of Isolated Magnetic Profile Using Simulated Annealing Approach

Understanding the magnetic anomaly in terms of the subsurface causative source plays a pivotal role in mineral exploration as well as in other geological applications. Automatic modeling of such isolated profile data is still rising, and fundamental improvements are needed in analyzing the association of subsurface rocks with the magnetic anomaly in terms of various independent model parameters. Here, we propose a MATLAB-based simulated annealing algorithm to simplify the interpretation process of magnetic anomalies. The performance of the adopted approach over various synthetic models of simple geometries like spheres, dikes, sills, and prisms is analyzed with and without contaminated noise. These geometries are widely used for some specific types of ore bodies such as iron, base metals, and mineralization such as skarns, massive sulfides, etc. Finally, two different real deposits of Chromite Ore and Uranium Ore are taken along with their magnetic anomalies to interpret their subsurface geometries in terms of model parameters. The estimated structures are verified to have a great affinity with the structures obtained in previously published works of literature. Furthermore, the present computational algorithm provides a user-friendly approach without any computational difficulties with minimum cost.