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The presence of remanent magnetization brings uncertainty to the processing and interpretation of magnetic data. Therefore, separating the contributions of the remanent magnetization from the total magnetic data is always the research hotspot. In the literature, numerous methods have been introduced to handle this issue. However, most of the existing methods are complex to calculate, have strict requirements on magnetic sources, and need prior information. In this study, a new method for automatically separating the total magnetic anomalies into the components due to induced and remanent magnetization based on deep learning has been presented. The presented method designs an end-to-end network structure based on the U-Net network structure and then performs continuous training and parameter optimization to determine the optimal network structure. Afterward, the presented method is tested on synthetic examples and actual magnetic data in Yeshan Region (Eastern China). The results demonstrate that the presented method can separate anomalies by induced and remanent magnetization. [ABSTRACT FROM AUTHOR]

The analytic signal (AS1) has been widely used for mapping geological features from magnetic data. Some enhanced versions of the AS1 have been introduced to improve its effectiveness. Here, we compare the performance of these filters and introduce a filter obtained from the tilt angle and the directional analytic signals. For better performance on low latitudes, the directional analytic signals are obtained from the vertical integral of the magnetic anomaly rather than its magnetic potential. The proposed filter shows an apparent performance improvement in mapping the edges of magnetic sources, as shown with synthetic models and real example from the Olympic Peninsula, USA. The great advantage of the proposed technique is that the obtained result has lower influence from the magnetization vector direction than the AS1 and other related techniques. The findings demonstrate that the present method not only outlines the boundaries more precisely and clearly, but also reveals the presence of several structures obscured by nonmagnetic sediment in the study area, which are not determined by other methods. [ABSTRACT FROM AUTHOR]

The total magnetic intensity (TMI) image of the southernmost part of the Indian peninsular shield exhibits a conspicuous NW-SE trending mega lineament of 200 km, associated with Achankovil Suture Zone (AKSZ) across the Southern Granulite Terrain (SGT) that evolved during East African Orogeny. This crustal scale anomaly of 200 nT amplitude, is significant to understand the regional tectonics and the possible linkage between AKSZ and Ranotsara Shear Zone (RSZ) of Madagascar. The structural trends are inferred from magnetic data surrounding AKSZ and RSZ to reconstruct the Gondwana fragments of the SGT and south Madagascar. The aeromagnetic images of conjugate rifted fragments of this part of India and Madagascar are connected well on both sides: the Madurai block with Antananarivo domain and Trivandrum block with Anosyan domain, north and south of AKSZ-RSZ respectively. Magnetic modelling across AKSZ reveals a hidden subsurface basic body suggesting a deep geofracture. We infer the sequence of tectonic development of the AKSZ as: (i) the subduction-accretion process in amalgamation of continental fragments to form Gondwana supercontinent during the Late Neoproterozoic and (ii) Pan-African exhumation of anomalous sub-crustal material. [ABSTRACT FROM AUTHOR]

Crustal magnetic anomaly maps over oceanic regions are based largely on marine trackline surveys. These surveys, collected from the 1950s to the present, span a wide range of data quality and reliability. We discuss a methodology for constructing grids from these data with associated cell by cell estimates of grid uncertainty. The method is tested with a modern airborne survey for a representative region in the eastern Caribbean. The results are promising, producing an uncertainty estimate that is accurate to one standard deviation for the test area. As magnetic anomaly maps and grids are increasingly applied as constraints for geologic interpretation as well as for alternative navigation (e.g., navigation by magnetic field patterns in the absence of GPS), it is important to quantify the accuracy of these maps. Plain Language Summary: It is challenging to make maps of the variations in the Earth's magnetic field, called crustal magnetic anomalies, caused by the distribution of magnetic minerals in oceanic areas. The reason for this is that the best available data for most marine areas is from ship‐based measurements collected over many decades, from the 1950s to the present. The spatial distribution of these marine survey tracklines is highly variable as is their original data quality and reliability. Previous grids and maps constructed from marine trackline data have not included systematic estimation of the grid/map uncertainty. At best, earlier maps have included generalized statements about the estimated mean uncertainty. In this study, we present a methodology for estimating the crustal magnetic anomaly and the associated uncertainty from marine trackline data. The method is evaluated using a modern airborne survey of a test area in the eastern Caribbean, an area surrounding St. Croix in the US Virgin Islands. Key Points: Marine crustal magnetic anomaly maps are typically constructed from trackline data with variable uncertainties and spatial configurationsThis paper presents a methodology for creating data grids with associated cell by cell uncertainty from marine trackline dataThe method is tested against newly collected modern airborne magnetic data [ABSTRACT FROM AUTHOR]

Coal fires are a global environmental and social catastrophe, which deteriorate air quality, destroy the surface vegetation and soil, and pollute groundwater. The delineation of coal fire scope and the location of the fire source are indispensable for the efficient control of them. In this paper, three different geophysical methods, including magnetic method, self-potential method, and electrical resistivity tomography (ERT), are adopted to detect coal fires. Upward continuation is conducted with magnetic data and self-potential data to highlight the net anomaly due to coal fires and to suppress the noise from the background geomagnetic field and geoelectric field. The scope of the fires is delineated by magnetic and self-potential anomalies in 2D and is compared with the borehole temperature data. Furthermore, self-potential data is inverted by an iterative compaction constrained inversion algorithm with the assistance of resistivity data. The inverted fire source location, which is represented by the source current density, is consistent with field survey results. The findings are critical to determine the scope and source of underground coal fires. [ABSTRACT FROM AUTHOR]

A zone of significant high-amplitude magnetic anomalies is observed without a comparable gravity high along the Cascadia margin and is spatially correlated with the low-velocity fore-arc mantle wedge. This wedge is interpreted to be serpentinized fore-arc mantle and is further considered to be the main source of the high-amplitude magnetic anomalies. To test this hypothesis, the magnetization-density ratio (MDR) is estimated along the Cascadia margin to highlight the physical characteristics of serpentinization (reduced density and increased magnetization). Interestingly, high MDR values are found only in central Oregon, where slab dehydration and fore-arc mantle serpentinization (50–60% serpentinization) are inferred in conjunction with sparse seismicity. This result may indicate either poorly serpentinized fore-arc mantle (low degree of serpentinization) or that the fore-arc mantle is deeper than the Curie temperature isotherm for magnetite in northern and southern Cascadia. This finding means that magnetic anomaly highs and serpentinized fore-arc mantle may not always be correlated in subduction zones. On the other hand, the MDR pattern suggests segmentation of the Cascadia subduction zone, which is consistent with several previous geological and geophysical observations. [ABSTRACT FROM AUTHOR]

The paper deals with the description of new geomagnetic data collected in the North Atlantic during cruises of research vessels of the Russian Academy of Sciences performed in 2020–2022. Modern technologies of geomagnetic measurements in the ocean and methods of their processing are considered. The obtained geomagnetic data indicate the heterogeneous nature of the sources of magnetic anomalies in the Charlie–Gibbs fracture zone and adjacent areas of the Mid-Atlantic Ridge and allow solving a wide range of geological and tectonic problems. Priority directions for further research aimed at adjusting spreading parameters and constructing models of the magnetic layer typical for transform faults and amagmatic segments of the Mid-Atlantic Ridge are formulated. [ABSTRACT FROM AUTHOR]

Granite and gneiss buried hill reservoirs are controlled by their lithology and dark mineral content. Therefore, lithological identification and dark mineral content analysis are important research tools in the early stage of buried hill exploration. In this paper, the relationships between the seismic facies and lithology, magnetic susceptibility, and magnetic anomalies of granite and gneiss are analyzed based on the lithological characteristics of the LiShui depression (LS depression) in the East China Sea Basin (ECSB). The waveform classification method is used to identify granite and gneiss, and the waveform classification results reveal that areas with continuous distribution of a single seismic trace model or two seismic trace models represent good continuity, and can be interpreted as gneiss. Areas with a mixed distribution of multiple seismic trace models represent chaotic and poor continuity, which can be interpreted as granite. The mixed linear zone with multi-seismic trace models is a fault zone, and the rock is cataclasite. In addition, reduction to the pole (RTP) and downward continuation technique for magnetic data processing were used to determine the dark mineral content. Overall, the granite and gneiss can be divided into three types based on magnetic anomaly data: high, moderate, and low magnetic anomaly areas. The areas in which granite with moderate and low magnetic anomalies is distributed are the favorable exploration target areas. The above method provides a technical means of lithological identification in the early stage of buried hill exploration. [ABSTRACT FROM AUTHOR]

Automated interpretation of geologic features using an improved deep learning technique is a useful and progressively more acceptable tool in modeling magnetic anomalies in derivative maps. An improved deep learning model was employed to analyze magnetic derivative maps for concealed structures controlling mineralization within southwestern Nigeria's schist-belt. This model was developed to reproduce signatures of geological features with corresponding magnetization amplitude into valid exploration criteria. This was developed by incorporating a feature engineering phase on an existing deep learning model - resunet. The automation process speeds up extraction processes and also fast-track other decision-making processes. The added phase removes noise and also strengthens the critical edge structure of magnetic images. An experiment carried out on a publicly available dataset shows promising results. [ABSTRACT FROM AUTHOR]

Two‐dimensional modeling of gravity and magnetic anomalies in terms of polygonal bodies is a popular approach to infer possible configurations of geological structures in the subsurface. Alternatively to the traditional trial‐and‐error manual fit of measured data, here we illustrate a probabilistic strategy to solve the inverse problem. First we derive a set of formulae for solving a 2.75‐dimensional forward model, where the polygonal bodies have a given finite lateral extent, and then we devise a Hamiltonian Monte Carlo algorithm to jointly invert gravity and magnetic data for the geometry and properties of the polygonal bodies. This probabilistic approach fully addresses the nonlinearity of the forward model and provides uncertainty estimation. The result of the inversion is a collection of models which represent the posterior distribution, analysis of which provides estimates of sought properties and may reveal different scenarios. Plain Language Summary: A probabilistic Monte Carlo method to infer the shape and properties of geological bodies in the subsurface from gravity and magnetic data is discussed in this paper. The geological bodies are represented as polygons with constant density and magnetic properties. The results of applying the proposed algorithm is a collection of models of the subsurface that can be statistically analyzed to infer structure and properties of the subsurface. Key Points: Contrary to the traditional manual approach, an objective procedure to jointly invert gravity and magnetic anomalies for 2.75D polygonsSampling using gradient information is an efficient nonlinear strategy to explore plausible solutions, where deterministic methods failInterrogation of the collection of posterior solutions provides statistical answers to complex questions including uncertainty estimation [ABSTRACT FROM AUTHOR]

Despite the prevalence of well-established and explored navigation systems, alternative localization methods are currently the focus of intensive research. This interest is driven by geopolitical challenges and increasingly sophisticated applications of mobile robots and uncrewed aerial vehicles. This study investigates the problem of real-time positioning in GPS-denied environments. Based on the mapped magnetic anomaly field and using Bayesian formalism for data fusion, the localization obtained from embedded sensors is corrected to reduce cumulative errors. The proposed method has minimal computational cost and a minimal number of tunable parameters. The paper introduces it and demonstrates its effectiveness in a laboratory study. Experimental tests, using a system equipped with an Inertial Measurement Unit, demonstrated a significant reduction in localization uncertainty. The improvement was especially notable in areas with large, smooth variations in the magnetic field. Finally, the accuracy of the method is analyzed, and its performance is compared to a particle filter. • The paper proposes a framework for a magnetic navigation module. • The module utilizes local anomalies of the magnetic field. • In GPS-denied environments, magnetic corrections improve the IMU-based localization. • When the reference position is available, the module maps the magnetic anomaly field. • A lab-scale verification and a comparison to the particle filter are provided. [ABSTRACT FROM AUTHOR]

In this work, we calculated the Curie Point Depth (CPD) for the Brazilian Equatorial Margin using the Fourier and continuous wavelet (CWT) transforms considering a linear inversion for random and fractal magnetization models with four different magnetic datasets. After comparing our results with Curie maps reported by previous studies, we concluded that the more consistent Curie isotherm was obtained by applying the random model based on CWT to the Brazilian Equatorial Margin Magnetic Map dataset, a compilation of airborne and marine magnetic surveys complemented with magnetic anomaly data extracted from the World Digital Magnetic Anomaly Map in the deep-water oceanic domain. In addition, we estimated heat flow using CPD results and compare with a global heat flow model based on geothermal measurements. In the continental domain, Curie values range from 18 to 35 km, shallowing westwards until reaching anomalously 10 km in the Tocantins Province. In turn, the heat flow decreases eastwards from 88 to 58 mW/m2 as the Curie depth increases within the continental crust. Meanwhile, in the deep-water oceanic domain, the heat flow is overall higher (between 72 and 87 mW/m2), indicating a younger and warmer oceanic crust, whereas the Curie isotherm is shallower, varying between 10 and 30 km. Even so, it is deeper than Moho, suggesting a magnetized lithospheric mantle. [ABSTRACT FROM AUTHOR]

The cartography of lineaments across a territory can be optimized using geophysical potential field data. In this study, land gravity and EMAG2 (Earth Magnetic Anomaly Grid) data were simultaneously used to identify and characterize the major lineaments that spread across Cameroon. The data were filtered using a multi-scale approach including horizontal and vertical gradient analyses. The Euler Deconvolution method was later applied to the filtered data to estimate the extension and depth of the identified lineaments. Results show that the main lineaments across Cameroon are laterally extended with a dominant N45°E orientation. Some of these lineaments correlated well with the geographical location of some known major tectonic structures found across the country. The depth of these lineaments varies between 1 and 35 km. Some of the identified faults are still active as their location correlated with the location of some recent earthquakes that occurred in Cameroon. This work, therefore, highlights some hidden tectonic features which knowledge generally precedes exploration for subsurface resources. [ABSTRACT FROM AUTHOR]

The vector transformation and pole reduction from the total-field anomaly are significant for the interpretation. We examined these industry-standard processing procedures in the Fourier domain. We propose a novel iteration algorithm for regional magnetic anomalies transformations to derive the vertical-component data from the total-field measurements with the variation in the core-field direction over the region. Additionally, we use the same algorithm to convert the calculated vertical-component data into the corresponding data at the pole and realize the processing of differential reduction to the pole (DRTP). Unlike Arkani-Hamed's DRTP method, the two types of iterative algorithms have the same forms, and DRTP is realized by implementing this algorithm twice. The synthetic model's calculation results show that the method has high accuracy, and the field data processing confirms its practicality. [ABSTRACT FROM AUTHOR]

Magnetic anomaly navigation is gaining popularity as an alternative-navigation system that addresses the challenges of GPS denial. Magnetic anomaly navigation has recently been flight test proven on an F-16 aircraft. The corrupting magnetic environment on this operational platform is 2–3 orders of magnitude larger than previous flight-tests on geo-survey aircraft, while also displaying stochastic drift. The difficult magnetic environment of the platform necessitated a combination of batch and online calibration to obtain accurate navigation solutions. Superiority of the new method is shown in comparison to prior published methods. Real navigation results on the F-16 are shown to obtain accuracies 50% better than these competing methods, with low-altitude results obtaining 59-m distance root-mean-squared errors on 1.5 h flights versus 111 m using batch-only calibrations. [ABSTRACT FROM AUTHOR]

The Tikhonov regularization downward continuation (TRDC) is one of the most robust methods to enhance magnetic anomalies, where the determination of an optimum value of the regularization parameter is a crucial task. In this study, we propose an iterative Tikhonov regularization downward continuation (ITRDC) strategy to downward continue magnetic anomalies with no sensitives to the regularization parameter, which is beneficial for accurate downward continuation. We show that using some arbitrary values for the regularization parameter in the proposed ITRDC method, the expected downward continued field can be obtained by a series of iterations. Based on synthetic and field data examples using a large continuation distance of 40 times of the data spacing, we show that the proposed method is more accurate and stable than the standard TRDC. • We propose an iterative Tikhonov regularization downward continuation (ITRDC). • The proposed ITRDC method is insensitive to the regularization parameter (λ). • Using an arbitrary λ in the proposed ITRDC could still lead to expected results. [ABSTRACT FROM AUTHOR]

The Weihe basin possesses abundant in medium-low temperature geothermal resources. However, the primary source of heat in the basin, whether it stems from the mantle or crust, remains a subject of debate. In this study, we employ three-dimensional inversion of gravity and magnetic anomalies to ascertain the basement depth, Moho depth, Curie point depth, and spatial distribution of magnetic bodies within the Weihe basin. Our findings reveal that there is no correlation between heat flow and mantle uplift and the uplift area of the Moho does not coincide with the depocenter of the basin. These results suggest that the mantle heat brought by lithosphere thinning and stretching is not the predominant heat source in the Weihe basin. Furthermore, we observe a significant discrepancy in Curie point depth between the northern and southern sides of the Weihe fault within this region, indicating its role as a suture zone connecting two structural units throughout geological history. Through three-dimensional susceptibility inversion analysis, we identify a widespread distribution of magnetic bodies (primarily Yanshanian granites) beneath sediments within the Weihe basin which are connected to the granites located in the North Qinling area. This suggests that the granites formation within the Weihe basin may have occurred concurrently with the magmatic activity in the North Qinling area. Since Cenozoic timescale, northeastward compression exerted by the Tibet Plateau has resulted in passive strong fault depression within the Weihe basin while burying the previously intruded granites under thick sedimentary layers on a massive scale. These buried granites release heat through radioactive decay processes making them an essential heat source for the medium-low temperature geothermal fields. • Thermal structure of the Weihe basin is revealed by 3D gravity and magnetic inversion. • Mantle heat caused by lithosphere thinning is not the dominant heat source. • The Weihe basin is passively extensional rifted as Tibetan plateau moves to the northeast. • The Weihe basin has been devoid of magmatic activity since its formation. • The dominated heat source of the Weihe basin is radioactive heat production of granites. [ABSTRACT FROM AUTHOR]

The southern Indian Ocean has several prominent aseismic ridges recognized as oceanic large igneous provinces (i.e., the Madagascar Ridge, Del Cano Rise, Crozet Plateau, and Conrad Rise) in the off‐axis areas of the Southwest Indian Ridge (SWIR). However, previously obtained magnetic survey lines are sparse and not correctly aligned with the seafloor spreading direction; thus, the detailed spreading history, including the formation of these aseismic ridges, remains an open question. We reconstructed the tectonic history of two segments between the Discovery II and Gallieni fracture zones in the SWIR using newly obtained magnetic data (total and vector magnetic field) and an open‐source magnetic data set. We revealed that the southern Madagascar Ridge and the Del Cano Rise once formed a single bathymetric high and separated by at least Chron 30y, which is quite different from the global age model. In addition, the rises may have formed before Chron 34y, assuming an extinct ridge south of the Del Cano Rise. The two rises have been recognized as having formed by Marion hotspot plume‐induced excess volcanism around the active spreading ridge of the SWIR, which can explain locally isostatically compensated thicker‐than‐normal crust. However, linear magnetic anomalies have not been observed across the main part of these rises, suggesting that magmatic activity controlled by seafloor spreading is unlikely. Like other aseismic ridges in the southern Indian Ocean, these two rises may possibly have been formed partly by continental fragments rather than plume‐induced excess volcanism. Plain Language Summary: The southern Indian Ocean contains several bathymetric high regions previously interpreted as oceanic large igneous provinces. Hotspot‐ridge interaction is considered as the key factor in the formation of such large volcanic structures. However, the detailed seafloor spreading history and origin of these large volcanic structures are not understood as well as those in other oceans because of the vast and remote Indian Ocean. We conducted magnetic surveys and reconstructed a new tectonic history of two segments along the Southwest Indian Ridge (SWIR). We found that the southern Madagascar Ridge and the Del Cano Rise once formed a single bathymetric high and that they separated by at least 66 million years ago. Moreover, the rises may have formed before 84 million years ago, assuming an extinct ridge south of the Del Cano Rise. The two rises might have formed by interaction between the Marion hotspot and SWIR; however, linear magnetic anomalies implying seafloor spreading are not observed in the main parts of these rises. This absence suggests that hotspot‐ridge interaction cannot fully explain the origin of these rises. We cannot exclude the possibility that the two rises are partly continental fragments rather than products of hotspot‐induced excess volcanism. Key Points: Revised seafloor ages up to Chron 31 in the Indian Ocean are obtained by new total and vector magnetic dataOur new tectonic scenario indicates that the Madagascar Plateau and Del Cano Rise once formed a single bathymetric highThe tectonics of oceanic plateaus in the Indian Ocean need to be reexamined, including continental fragment origin [ABSTRACT FROM AUTHOR]

By establishing two solar‐wind convection electric field‐associated coordinate systems, the magnetic and plasma properties in the lunar wake are examined. In the plane perpendicular to the interplanetary magnetic field, all the properties exhibit asymmetric distributions related to the electric field, and they are even periodically modulated every two lunar radii but only along the flank which the electric field points to. Evidences show that the solar‐wind ions, reflected over the dayside lunar magnetic anomalies, have produced these asymmetries and periodical modulations. These ions, undergoing both the electric drift and large‐radius gyration, bypass the Moon body and periodically penetrate into the wake flank, during which they exchange momentum with the refilling solar‐wind plasma, thereby resulting in the oscillations of the plasma and the periodical modulations of the wake. Plain Language Summary: The lunar wake, produced by the solar‐wind plasma absorption on the dayside lunar surface, has been expected to be symmetric about the plane of the solar‐wind velocity and the interplanetary magnetic field. The solar‐wind convection electric field, which is perpendicular to that plane, has been found to be able to make asymmetric magnetic perturbations but only ahead of the lunar terminator, its influences to the magnetic field in the downstream wake, however, have not been noticed, yet. In this study, the reflected solar‐wind ions from the dayside lunar surface, biased and accelerated by the solar‐wind electric field, are found to be able to bypass the Moon, periodically penetrate into the wake flank which the electric field points to, and modulate the refilling plasma in the direction perpendicular to the magnetic field. The periodical modulations, thereby, produce an asymmetric and meandering wake as observed. Key Points: The central lunar wake meanders in phase with the gyromotions of the reflected ions in the solar‐windThe reflected solar‐wind ions periodically modulate the wake refilling plasma, thereby producing the meandering wakeThe magnetic field and the plasma properties in the wake are all modulated along with the meandering structure [ABSTRACT FROM AUTHOR]

Abstract—The formation of impact craters on the Earth's surface is accompanied by the effect of shock waves on rocks. The shock wave compression results in rocks heating up to the point of melting and evaporation during unloading. The direct mechanical action of shock compression and residual heating change the magnetic properties of rocks. Geophysical modeling is used to determine the sources of the magnetic anomaly by interpreting the fields measured on the surface, but such modeling does not take into account the impact demagnetization of rocks. This work gives an example of analysis of the magnetic anomaly over the well-studied Bosumtwi crater (Ghana, 10.5 km diameter, 1 million years old), including the numerical modeling of the crater formation process and the construction of a magnetic anomaly model based on the simulated shock compression parameters and crater drilling data. It is shown that the morphological features of the crater— the crater rim and the central uplift—form positive magnetic anomalies around and inside the crater. [ABSTRACT FROM AUTHOR]

In recent times, studies about remote-sensing methods have focused on improving variables like sensing distance, sensitivity, and power consumption of available remote-sensing methods. The main target of this study is to improve these variables for the magnetic anomaly detection (MAD) method, in addition to determining upper surface geometry of the sheath with the support vector machine (SVM) algorithm to allow detection of buried ferromagnetic-sheathed explosives, minimize the number of false alarms, and thus shorten the scanning time. The classification process with the SVM algorithm separates this study from others. In line with this, instead of an external magnetic field source, in this study, the Earth’s magnetic field was used with a TE100 fluxgate sensor, which has very low power consumption, used as a magnetic sensor to develop a highly sensitive new magnetic measurement and detection system. The system identifies anomalies in the vertical component of the Earth’s magnetic field due to the magnetic characteristics of the buried sample in order to determine both the coordinates of the buried object within the scanning field and the upper surface geometry. The system is formed using a five-axis movement CNC platform including sensors and camera. Software was developed using python programming language with a QT graphical user interface (GUI) in order to control the CNC platform, take photographs of the soil, and process sensor data to ensure identification of the upper surface shape of the object under the soil. After obtaining all data for a 30 × 30 cm2 scanning area, the software colors the data from blue to red and visualizes this transparently above a photograph of the soil on the monitor. After this stage, a model is created using thresholding, selective search algorithm, and SVM in order to identify the location and upper surface shape of the sample located within the measurement region. Tests performed after SVM training determined the system can classify the upper surface geometry of buried samples with 88% success. [ABSTRACT FROM AUTHOR]

Attitude information obtained from low-cost magnetic, angular rate, and gravity (MARG) sensors is prone to be deteriorated by disturbances such as external acceleration and magnetic anomaly in operational environments. To address the problem, a robust attitude estimation algorithm using low-cost MARG sensors is proposed. An error state Kalman filter (ESKF) is used for data fusing, in which the attitude errors are interpreted as a small rotation vector, and the gyro bias variation is also estimated. The nominal state and the error state are propagated with unit quaternion and rotation vector, respectively. An attitude correction is followed which combines the nominal and error parts by quaternion multiplication. The robustness of the proposed algorithm is embodied in resisting accuracy degradation of the attitude estimation caused by both external acceleration and magnetic anomalies. While external accelerations and magnetic disturbances are detected online, the accuracy reduction in attitude estimation is prevented by adaptively adjusting the related measurement noise covariance matrix. Besides, a two-step measurement update strategy is designed to guarantee that the roll and pitch update is separated from the yaw update. Various rotation and land vehicle dynamic tests have been conducted to validate the effectiveness and robustness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Knowledge of the shock remanent magnetization (SRM) property is crucial to interpret the spatial changes in magnetic anomalies observed over the impact crater. This study reports the spatial distributions of SRM intensity and stability of single‐domain titanomagnetite‐bearing basalt based on the SRM acquisition experiments using a two‐stage light gas gun with Al projectiles, remanence measurements for divided subsamples, and impact simulations. The SRM properties systematically change with increasing pressure, and three distinctive aspects are recognized at different pressure ranges: (1) constant intensity below 0.1 GPa, (2) linear trend as intensity is proportional to pressure up to 1.1 GPa, and (3) constant intensity and increasing stability above 1.9 GPa. The SRM intensity and stability distributions suggest that the crustal rocks containing the single‐domain titanomagnetite originally had an SRM intensity distribution according to the distance from the impact point, which changed depending on the remanence stability after the impact. Plain Language Summary: Shock remanent magnetization (SRM) is acquired as a result of the shock wave propagation in a magnetic field. Knowledge of a three‐dimensional distribution of the SRM intensity and stability is crucial for interpreting the spatial change in magnetic anomalies observed over the impact crater and reconstructing the paleo‐planetary field based on the anomaly data. Here, we report the SRM intensity and stability structures of fine‐grained single‐domain titanomagnetite‐bearing basalt based on the newly designed study protocol such as the SRM acquisition experiments, remanence measurements for divided subsamples, and impact simulations. The SRM properties systematically change with increasing pressure, and three distinctive aspects are recognized at different pressure ranges. The systematic changes in the SRM intensity and stability suggest that the crustal rocks containing the single‐domain titanomagnetite originally had an SRM intensity structure at the time of impact, and this structure changed depending on the remanence stability after the impact. Key Points: The shock remanent magnetization (SRM) acquisition experiments and impact simulations were conducted to reveal the SRM intensity and stability distributionsThe SRM properties systematically change with pressure, and three distinctive aspects are recognized at different pressure rangesThe SRM intensity varied with the distance from the impact point, which changed depending on the remanence stability after the impact [ABSTRACT FROM AUTHOR]

Since the '60s of the last century, the calculation of the magnetic anomalies caused by 2D uniformly polarized bodies with polygonal cross‐section has been mainly performed using the popular algorithm of Talwani and Heirtzler (1962, 1964). Recently, Kravchinsky et al. (2019, https://doi.org/10.1029/2019GL082767) claimed errors in the above algorithm formulation, proposing new corrective formulas and questioning the effectiveness of almost 60 years of magnetic calculations. Here we show that the two approaches are equivalent and Kravchinsky et al.'s formulas simply represent an algebraic variant of those of Talwani and Heirtzler. Moreover, we analyze a large amount of random magnetic scenarios, involving both changing‐shape polygons and a realistic geological model, showing a complete agreement among the magnetic responses of the two discussed algorithms and the one proposed by Won and Bevis (1987, https://doi.org/10.1190/1.1442298). We release the source code of the algorithms in Julia and Python languages. Plain Language Summary: Forward magnetic calculation plays a major role in geophysics to model magnetization, location, and shape of magnetic sources. One of the most popular approaches to calculate magnetic anomalies due to two‐dimensional bodies is based on the formulas of Talwani and Heirtzler (1962, 1964), that have been widely used both for scientific and industrial applications from the sixties. Recently, these formulas have been questioned by Kravchinsky et al. (2019, https://doi.org/10.1029/2019GL082767) casting doubts on the truthfulness of all the magnetic models and interpretations obtained to date. We examined and compared the two calculation approaches, both from an analytical and numerical point of view. In detail, we corrected some inaccuracies in Kravchinsky et al.'s formulas and we found complete equivalence between the two discussed formulations, showing that they simply represent two algebraic variants of the same mathematical approach. We also performed intensive numerical tests comparing the results of the two algorithms with a third one proposed by Won and Bevis (1987, https://doi.org/10.1190/1.1442298). The three mathematical approaches gave the same magnetic responses for all the tested models, demonstrating total agreement between the three formulations. Key Points: Kravchinsky et al. (2019) claimed errors and omissions in the formulas of Talwani and Heirtzler (1962) for 2D forward magnetic calculationOur analysis reveals that Kravchinsky et al.'s formulas are algebraically equivalent to those of Talwani and HeirtzlerNumerical tests show a complete agreement among the two above formulations and the one by Won and Bevis (1987) [ABSTRACT FROM AUTHOR]

We have developed a new method for the interpretation of a magnetic anomaly profile by idealized-geometrical bodies using the variance analysis. This method is based on estimating the fourth horizontal derivative of the magnetic data profile. The advantage behind the use of the fourth horizontal derivative method is to reduce the regional background effect. The model parameters estimated are the depth and shape of the buried body using all available window lengths (s-value). Then, the variance value for the calculated depth at each shape value is estimated using all available s-values. The minimum variance is considered as the best criterion for determining the best-inverted parameters (depth and shape). The developed method has been verified on some noise free examples. Following that, the accuracy of the method was assessed by studying the impact of synthetic data with 5%, 10%, and 15% random noise, the effect of the regional background, the influence of interfering structures, and the selection for the wrong origin of the body. The presented method has been successfully applied to three real case studies from Brazil and India from mineral exploration. [ABSTRACT FROM AUTHOR]

A coupled 3D geophysical–geological model was constructed by integrating aeromagnetic data and a prior 3D geological model of the Morungava region (Araújo et al., 2023 [manuscript submitted for publication]), situated at the southeastern border of the Paraná–Etendeka large igneous province (LIP) in Brazil. Aeromagnetic data interpretation and modeling (qualitative and semi-quantitative interpretation, susceptibility inversion, forward modeling, and magnetic vector inversion (MVI)), along with magnetic susceptibility data, complemented understanding of the Serra Geral Group feeder system in the subsurface (spatial distribution, depth, and geometry) and illuminated the crustal framework at different depths. We recognized three major NE-elongated geophysical domains (NW, Central, and SE), which were interpreted as basement compartments: the Tijucas, Pelotas, and Jaguarão terranes. The final integrated 3D geophysical–geological model encompasses the stratigraphic framework and the Serra Geral Group plumbing system in the study area, that comprises: two dike systems, four subvolcanic complexes with associated nested sills, and two intrusive ring complexes. This is the first time that these aeromagnetic data have been combined with borehole and 3D geological models. • Matched-filter analyses to interpret magnetic anomalies in depth. • Combined magnetic data inversion and 2.5D forward modeling. • 3D geological-geophysical model. • Intrusive ring complex in southern Paraná-Etendeka LIP (Brazil). • Shallow anomalies related to components of the Serra Geral Group plumbing system. [ABSTRACT FROM AUTHOR]

The Sivas Basin is located in the eastern part of the central Anatolia. In this study, aeromagnetic data in the basin and surrounding area are processed and anomalies are interpreted to determine the approximate locations of the causative bodies and reveal their relationship with the tectonic trends. The sedimentary basin is surrounded by strong magnetic anomalies from the south, east, and northeast. The most apparent anomalies are observed in the E-NE of Zara, SW of Divriği, and north of Kangal. These anomalies do not present significant directional change when they are reduced to the pole process. Causative bodies of the southern anomalies around Divriği and Kangal extend from NE to SW and the northerly anomaly trend (to the north of Kangal) crosses the southern one (Divriği trend) in the analytic signal map. These trends are well-defined by the maxima points of the horizontal derivatives and these maxspots generally follow the boundaries of anomalies in the tilt angle map. The Kangal Fault controls the extensions of the Divriği anomalies through the north and they are not observed in the area to the north of the fault. The Hafik Anomaly in the north of the study area is also differentiated from the anomaly group in the E-NE of Zara precisely, defining that they are created by 2 different causative bodies. Aeromagnetic characteristics of the ophiolites to the south indicate that they have different origin from the northern ophiolites group. Similarly, it is determined that the plutonic rocks in the south and north are also different origin emplacements, considering their aeromagnetic responses, mineral contents, and ore deposit possibilities. [ABSTRACT FROM AUTHOR]

Recent successful flight tests have demonstrated scalar magnetic anomaly navigation to be a viable GPS-alternative navigation system. These flight tests matched magnetic field measurements to maps of the Earth's crustal magnetic field in order to navigate. Scalar magnetic navigation uses only the magnetic field intensity, not direction, in order to navigate. While it appears obvious to extend aerial magnetic navigation to use the full vector field, in practice there are substantial obstacles to doing so. This article explores the key challenges of magnetic vector navigation including current sensor limitations, lack of high frequency magnetic vector maps of the Earth's crust, and proper integration of the magnetic data with an inertial navigation system. In overcoming these challenges several key benefits of magnetic vector navigation over scalar magnetic navigation become apparent, including modestly improved navigation accuracy and greatly improved platform attitude. [ABSTRACT FROM AUTHOR]

Nine total magnetic profiles in the S–N direction of the Central Indian Ocean (CIO) have been interpreted with spectral and Werner deconvolution techniques to obtain approximate depths to shallow (magnetic basement) and deeper (Curie isotherm) interfaces of the oceanic crust. From these preliminary depths, tentative crustal models for all these nine profiles are prepared. These tentative models of the area show varying thickness of the oceanic crust, supporting the deformation history. It is inferred from these tentative models that deformation extends beyond the zone identified south of 8°S latitude. There is good agreement between the spectral and Werner deconvolution depths. [ABSTRACT FROM AUTHOR]

Local phase filters as the tilt derivative (TDR) and the horizontal tilt derivative (TDX) are extensively used to interpret magnetic data. We use two combinations of these filters, namely TDR − TDX and TDR + TDX, to design a constraining mask that guides the Euler deconvolution moving data window. The TDR − TDX filter produces sharp peaks over the centers of the sources, while the TDR + TDX filter generates plateaus over them. Motivated by previous approaches that make use of the Laplacian filter or the analytic signal to constrain the Euler deconvolution window, we compute the solutions for windows centered at points that (1) have positive values of TDR − TDX and (2) are contained in the plateaus of TDR + TDX. The use of both criteria improves the selection of source-related points while reducing the number of spurious ones. Our method is tested in synthetic anomalies due to interfering dike-like sources and field data from southeast Brazil. The experiments show that the use of a constraining mask based on combined tilt filters produce Euler solutions that are more contiguous and less sensitive to noise than the traditional located-Euler deconvolution. [ABSTRACT FROM AUTHOR]

The boundary between South America and Scotia plates was established during Neogene times when a wrench tectonic regime was developed along the central area of Tierra del Fuego. This boundary includes the Magallanes–Fagnano fault system: a regional diffuse deformation zone, which involves the development of the satellite Yehuin–Chepelmut fault zone and a series of pull‐apart basins overprinting the Fuegian fold and thrust belt. The analysis of regional seismic lines allowed to reconstruct and recognize the structure of the external fold and thrust belt. The interpreted structures were integrated into a regional transect and a 3D block diagram that display the different structural domains and, mainly, the wrench deformation associated with the Magallanes–Fagnano fault system. Geophysical data from gravity and magnetic anomaly maps provided further support for the location and development of the pull‐apart basins along the plate boundary. The deformation of the external fold and thrust belt is characterized by an imbricated fan system with a Paleogene detachment surface, which was later cut across by the Yehuin–Chepelmut fault zone and the Magallanes–Fagnano fault system. [ABSTRACT FROM AUTHOR]

The impact crater formation on the surface of the Earth and other planetary bodies is accompanied by the action of shock waves on rocks and their displacement into a new position. The shock-wave compression results in the occurrence of the remanent heating of rocks (up to melting and evaporation during the unloading). The direct mechanical action of the shock compression and the remanent heating change the magnetic properties and magnetization, which leads to arising of the magnetic anomaly above the crater area. This work presents an example of the complex analysis of the magnetic anomaly above the well-studied impact crater Bosumtwi (Ghana, a diameter of about 10 km), including the numerical simulation of the crater formation process and the magnetic anomaly model on the basis of simulated parameters of shock compression. The complex model demonstrates a good agreement with data of direct measurements. [ABSTRACT FROM AUTHOR]

The difficulties in unravelling the tectonic structures, in some cases, prevent the understanding of the ore bodies' geometry, leading to mistakes in mineral exploration, mine planning, evaluation of ore deposits, and even mineral exploitation. For that reason, many geophysical techniques are introduced to reveal the type, dimension, and geometry of these structures. Among them, electric methods, self-potential, electromagnetic, magnetic and gravity methods. Global meta-heuristic technique using Whale Optimization Algorithm (WOA) has been utilized for assessing model parameters from magnetic anomalies due to a thin dike, a dipping dike, and a vertical fault like/shear zone geological structure. These structures are commonly associated with mineralization. This modern algorithm was firstly applied on a free-noise synthetic data and to a noisy data with three different levels of random noise to simulate natural and artificial anomaly disturbances. Good results obtained through the inversion of such synthetic examples prove the validity and applicability of our algorithm. Thereafter, the method is applied to real case studies taken from different ore mineralization resembling different geologic conditions. Data are taken from Canada, United States, Sweden, Peru, India, and Australia. The obtained results revealed good correlation with previous interpretations of these real field examples. [ABSTRACT FROM AUTHOR]

The Sichuan Basin magnetic anomaly is the most striking regional aeromagnetic anomaly in South China. It is characterized by a continuous large-scale linear magnetic anomaly and contains long-wavelength constituents which could still be detected on satellites. However, Sichuan Basin is covered by 4 to 10 km thick non-magnetic sedimentary layers from Neoproterozoic to Cenozoic, which conceals the magnetic sources in the Precambrian basement and makes it difficult to explore the geological origin of the Sichuan Basin magnetic anomaly. In this study, we applied 3D inversion to the magnetic data, and then compared our inverted susceptibility model with geological maps. We found that the spatial distribution of the Sichuan Basin magnetic anomaly controls the range of the rigid basement beneath Sichuan Basin and it is surrounded by the widespread Neoproterozoic magmatic complexes. Based on our analysis, we proposed that the geological origin of the Sichuan Basin magnetic anomaly might be related to the craton-scale Neoproterozoic magmatic event, which has played an important role in the stabilization of the basement and the evolution of the deep crust in Sichuan Basin. [ABSTRACT FROM AUTHOR]

The equivalent source is a simple and effective method to level and manipulate magnetic data. However, large misfits between the predicted and synthetic data for different components of the magnetic field are observed when a single layer equivalent source is used. Therefore, a dual‐layer equivalent sources method, based on a shallow‐layer and an additional deep‐layer is proposed. This technique successfully overcomes the inherent problem of inversion that equivalent property concentrates in the shallow layer, by changing the dimensions of deep equivalent cells, and by using a preconditioned matrix based on a weighted function, which enhances the effects of the deep layer. The results indicate that, by adding a deep equivalent‐source layer, this new method significantly improves the accuracy in the prediction of the three components of the magnetic field, especially for the long‐wavelength fields. Plain Language Summary: The total‐field magnetic anomaly (commonly expressed as ΔB) and the three components (Bx, By, Bz) of the magnetic field are sensitive to the magnetized bodies, which are present in the Earth's crust. Usually, only ΔB is measured in field experiments. The scalar ΔB cannot fully express the characteristics and the information embedded in the vector field. An effective way to solve this problem is to transform ΔB into the three components of the magnetic field, i.e., the vector field. Here, a dual‐layer equivalent source algorithm, which can be adapted to the measured magnetic anomaly (ΔB) and which is independent from their distribution and terrain relief, is proposed. The dual‐layer consists in a shallow equivalent‐source layer, which is located near the observation surface to recover the short‐wavelength field, and a deep equivalent‐source layer, which is located deep in the Earth's crust to retrieve long‐wavelength signals. Furthermore, an inversion algorithm with a preconditioned matrix is used to avoid physical‐properties concentrating at the shallow layer. The application of such technique on synthetic and real data shows that the proposed algorithm is stable, accurate, and presents fewer boundary effects when compared to previous methods in literature. Key Points: The dual‐layer equivalent source model is proposed to manipulate and transform magnetic anomaly into three componentsA preconditioned inversion algorithm was used to retrieve the magnetic parameters of the equivalent sourceThe proposed technique significantly reduces the misfit when transforming the three components of the magnetic field [ABSTRACT FROM AUTHOR]

In this study, Curie-point depth (CPD), geothermal gradient, radiogenic heat production, and heat flow maps were constructed based on different thermal conductivity coefficients using magnetic anomaly data for the Kars Plateau, which has the largest volcanic cover in Turkey. The bottom depths of the magnetic crust in the research area were revealed by the CPD map for the first time in this investigation. There are two apparent magnetic anomaly trends in the study area: the first is the Horasan–Senkaya–Sarikamis–Selim–Arpacay trend in the NE–SW direction, and the other is the Hanak–Ardahan–Arpacay trend in the NW–SE direction. Two other prominent elongations extend into the Ardahan–Gole–Senkaya and Kars–Digor axes. All these trends represent mountain chains and/or stratovolcanoes in the region, and no anomalies are observed around the non-volcanic outcrops. Curie depths are shallow, up to 14 km between Horasan and Kagizman towns, and 12 km in the northwestern part of the study area. Gradient values can reach 50 °C km−1 in the northwestern sector, together with the high heat flows represented by the 150 Wm−1 K−1 contours. The deepest CPD region lies between Gole and Susuz towns, where the geothermal gradient decreases to 27 °C km−1. Heat flows decrease 60 Wm−1 K−1 in the same area. An apparent gap around the Kars Plateau was observed in previous regional heat flow maps of Turkey by other authors (who used the bottom hole temperatures of boreholes and hot springs temperatures). This gap has been accurately filled from the results of this study, and geothermal exploration areas and the geothermal potential of the Kars Plateau have thus been determined for future exploration activity on the basis of the tectonic elements and earthquake data. [ABSTRACT FROM AUTHOR]

In order to study the magnetic characteristics and temporal and spatial distribution law of igneous rocks in the south‐western Tibetan Plateau, we calculated the RTP aeromagnetic anomaly based on the aeromagnetic anomaly data with scales of 1:200,000 and 1:1,000,000. Then, we separated the RTP aeromagnetic anomaly using the regularization filtering method and obtained the local magnetic anomaly and the regional magnetic anomaly in the study area. Combined with previous geological and geophysical studies, we analysed the features of the RTP aeromagnetic anomaly, the local magnetic anomaly, and the regional magnetic anomaly, studied the corresponding relationship between the igneous rocks and the magnetic anomalies, discussed the magnetic characteristics and temporal and spatial distribution law of igneous rocks, and determined the distribution of the concealed igneous rocks. The results showed that the ophiolites and the ultrabasic rocks display strong magnetic characteristics, and the basic rocks and the intermediate rocks display weak magnetic characteristics, and the acidic rocks display moderate‐strong magnetic characteristics in the study area. The study revealed that the magmatic activities display a decreasing tendency from south to north in the study area. There are five concealed Jurassic ophiolite belts in the Bangong‐Nujiang Suture Zone and the Yarlung Zangbo Suture Zone, and two concealed Jurassic ultrabasic rock belts in the Gangdise Block and the Qiangtang Block, and a lot of concealed acidic rocks are found in the Gangdise Block. [ABSTRACT FROM AUTHOR]

The very first computational and most referred in the literature algorithm of Talwani and Heirtzler (1964) for calculating of the magnetic anomaly caused by two‐dimensional irregular shape subsurface structure has particular fundamental and educational significance in geophysics theory. We re‐derive this algorithm from first principles and discuss previous derivation omissions. Our resulting solution differs from the original publication. Based on our new solution we present the two‐dimensional forward magnetic modeling software and associated tutorials which are available for download from the website www.ualberta.ca/~vadim/software.htm. Additionally, we include the computation of the remnant magnetization which can be found using already published apparent polar wonder paths. Key Points: New formulas to calculate the magnetic anomaly caused by two‐dimensional irregular shape subsurface structure are derivedThe very first and most cited Talwani and Heirtzler (1964) algorithm is re‐derived and compared to the new derivationSoftware for two‐dimensional magnetic forward modeling is developed for educational and industry use [ABSTRACT FROM AUTHOR]

The values of all the components of the magnetic induction vector and its first-order spatial derivatives are determined from the spatial distribution of the magnetic field parameter values at each point of the observation plane. The inverse problem is solved using the analytic eigenvector method. The execution of the proposed algorithm was simulated using real data of magnetometric studies in the geomagnetic field. [ABSTRACT FROM AUTHOR]

The evolution correlation between the North China Craton (NCC) and the Indian Shield (IND) is very important for plate reconstruction. Recently, more and more research results show that the NCC and IND had been pieced together in the Paleoproterozoic. In order to analyse the correlation between the NCC and IND, we use the latest gravity and magnetic data to study deep geophysical characteristics of the NCC and IND respectively, and we also use a two‐dimensional discrete wavelet transform method to discuss the division scheme of the basement tectonic unit in the Paleoproterozoic at the point of gravity and magnetic field. On the basis of gravity and magnetic anomalies, the NCC is divided into the Eastern Block, Western Block, and the Trans‐North China Orogen, which are further divided into the secondary tectonic zones and blocks. The IND is divided into the Southern Block, the Northern Block, and the Central Indian Tectonic Zone, and they also are further divided into secondary tectonic zones and ancient cratons. On the basis of that, according to the four Paleoproterozoic plate assemblage schemes proposed by predecessors, we compared the geophysical characteristics and the correlation through the regional gravity and magnetic anomalies between the two continents. The results show that the faults and tectonic boundaries in the Trans‐North China Orogen of the NCC correspond well to those in the Central Indian Tectonic Zone of IND. Moreover, the gravitational and magnetic anomalies in the Eastern Block of the NCC are quite similar to those in the Southern Block of IND, which shows that the NCC and IND might have been pieced together during the Paleoproterozoic. The geophysical result that verifies the correlation between the NCC and IND based on gravity and magnetic fields provides the evidence for Paleoproterozoic plate reconstruction and constrains the assembling patterns between the NCC and the IND. [ABSTRACT FROM AUTHOR]

Abstract The effects of fault processes on rocks commonly include a lowered magnetic susceptibility and an increased predisposition to erosion. We present a workflow that uses these characteristics of faults and geological observations to interpret a 3D fault network. The location of faults on the topographic surface is first interpreted by a multi-layer lineament mapping method that includes geological and geophysical data sets. We then demonstrate how magnetic intensity data can be used to estimate the dip of fault-related magnetic anomalies by performing 2D inverse modeling along profiles extracted from a magnetic intensity grid. The accuracy of the method is assessed by modeling the dip of low magnetic anomalies of known geometry created in a synthetic 3D magnetic susceptibility model. Modeled dips are consistently accurate to better than 5° for input dips >60°. A requirement of the method, however, is that the magnetic susceptibility contrast between the background field and the magnetic anomaly must be >75% for the anomaly to be accurately modeled. Comparison between fault orientations modeled from magnetic data and measured in the field in the Guichon Creek batholith confirms that the methodology can be successfully applied to brittle faults in real, albeit relatively simple geological environments. Highlights • Fault network at surface identified by lineament mapping using multiple data sets. • Magnetite oxidation in faults reduces magnetic susceptibility to form linear features. • Fault dips modeled along 2D profiles extracted from magnetic intensity grid. • Dip modeling accuracy better than 5° at input dip >60°. • 3D fault network built using lineament mapping, modeled dips and measured strike/dips. [ABSTRACT FROM AUTHOR]

Highlights • The basement structural evolution of North China Craton experienced three stages. • Faults, orogenic belts and rock series are basis for dividing basement tectonic units. • Gravity and magnetic anomalies are important basis for structural unit divisions. • Magnetic abnormalities well identify structural boundaries and faults. • Multi-scale decomposed Bouguer anomalies well reflect deep basement conditions. Abstract The tectonic divisions of the North China Craton (NCC) basement has always been a hot and yet unresolved topic. We collected the latest gravity and magnetic data, and then used a two-dimensional discrete wavelet transform method to decompose the Bouguer gravity anomaly of the NCC into the 1st to 8th Approximations and Details, respectively. We then compared the dynamic tectonic division schemes with the gravity and magnetic division schemes for the Precambrian basement at the end of the Neoarchean and Archean. Our results show that the 2nd-order Detail field of the Bouguer gravity anomalies is well consistent with the Paleoproterozoic tectonic divisions of the NCC by Zhao et al. (2005), for it clearly outlines the 3-unit layout of the Eastern and Western blocks and the central Trans-North China Orogen, with some anomalous zones identically trending with the dike swarms. Faults and volcanic rocks generally produce magnetic anomalies, but the main anomalous zones in the magnetic field are merely distributed around the plate boundaries of the NCC. It may indicate that the amalgamation of the NCC was mostly completed in the Paleoproterozoic. The 5th-order Detail field of Bouguer gravity anomalies of the NCC corresponds well with its tectonic division at the end of the Neoarchean, for it well reflects the general boundaries and axial trends of the Archean units. These Archean units are mainly separated into three Paleoproterozoic tectonic units by Paleoproterozoic tectonic boundaries, respectively. The magnetic anomalies within the Western and Eastern blocks have separately similarities with the Trans-North China Orogen. The 6th-order Detail fields, however, match well the boundaries of the 10 continental nucleii of the Archean NCC, but the anomalous distributions in the 6th-order Detail are also divided by the Paleoproterozoic tectonic borders. In view of the gravity and magnetic anomalies, it further reveals that the NCC basement may have experienced a dynamic evolutionary process from continental nucleation to micro-continental amalgamation, and to a final unified crystalline basement. [ABSTRACT FROM AUTHOR]

Abstract A prominent positive gravimetric and magnetic anomaly stands out in the region of the Guadalquivir-Portimão Banks, Gulf of Cadiz, off SW Iberia. The bathymetric and gravimetric highs have been interpreted as resulting from basement uplift occurred during Mesozoic rifting followed by overthrusting during the Alpine orogeny. However, we show that basement uplift alone does not account for the observed magnetic anomaly, implying that an additional magnetic source must be considered for an integrated model that fits with all the data. We present a new magnetic study that calls for the existence of a large magmatic body intruded beneath the Guadalquivir and Portimão Banks, the Guadalquivir-Portimão intrusion. We perform 3D inversion of magnetic data to obtain a susceptibility model that estimates the shape and extension of the intrusion. The modeled volume is constrained by estimation of regional Curie depth and the susceptibility model is limited to a realistic range, allowing interpretation in terms of rock nature. To clarify the relationship between the intrusion and the local lithospheric structure, we build 2D cross-sections integrating the modeled intrusion with recent crustal models and use 2D forward modeling to ensure that both the predicted magnetic and gravimetric fields fit the observed data. These sections show the Guadalquivir-Portimão intrusion emplaced along a lithospheric decollement within the necking domain of the Algarve rifted margin, across the lower and upper crust. It is suggested that is crosscuts Jurassic sedimentary sequences, suggesting that it intruded after continental rifting. Given the similarities with other onshore magnetic anomalies corresponding to Late Cretaceous alkaline intrusions, it is likely that the Guadalquivir-Portimão intrusion represents the southernmost expression of the Late Cretaceous alkaline magmatic event that affected both onshore and offshore West Iberia, becoming the fourth element of the enigmatic NNW-SSE trending alignment of Sintra-Sines-Monchique plutons, whose significance remains to be fully understood. Graphical abstract Unlabelled Image Highlights • The Guadalquivir-Portimão magnetic anomaly is not explained by basement uplift • 3D magnetic inversion calls for a ~80 × 20 × 10 km magmatic intrusion • The intrusion is along the necking domain of South Iberia rifted Tethyan margin • Intrusion emplaced into lithospheric detachment of Ocean Continent Transition • 300 km long N28°W alignment of four Cretaceous alkaline complexes in West Iberia [ABSTRACT FROM AUTHOR]

Abstract Laxmi Ridge, a prominent basement high feature with negative gravity anomaly in the northern Arabian Sea, is generally considered as stretched continental crust. However, recently it is proposed that the ridge could be an extinct spreading ridge. Ship-borne and satellite-altimetry derived bathymetry, gravity and geoid data over the Laxmi Ridge are analysed and modelled to determine effective elastic plate thickness (T e) and crustal structure beneath the ridge. The estimation of T e and compensation mechanism of the ridge are examined based on 3D coherence and admittance analysis considering surface and subsurface loads which involve computation of coherence and admittance between Mantle Bouguer Anomaly (MBA) and sediment corrected bathymetry. The best fit model reveals that T e is about 3–4 km and amplitude of subsurface load at Moho is approximately equal to the surface load. Low value of T e implies elastically weak lithospheric plate which can be attributed to either weakening of lithosphere by re-heating and underplating caused by the then nearby Réunion Hotspot or volcanic emplacement on the young oceanic crust. Further, all along the length of the Laxmi Ridge, the MBA is negative and its magnitude reaches up to 115 mGal, which indicates either presence of thickened crust or less dense mantle beneath the ridge. 2D crustal models suggest that underplating material is prevalent all along the Laxmi Ridge. High amplitude (>400 nT) magnetic anomaly over the southern part of the ridge reveals several lineations in WNW-ESE direction suggesting magma outpouring along week zones. Geoid to topographic ratio over the ridge is negative (−1.98 m/km), possibly indicating shallow subsurface load (<20 km) with small wavelength (<200 km). Based on present study and available geophysical results, we infer that the Laxmi Ridge is a stretched continental sliver which is underplated, intruded by volcanics and isostatically compensated by Airy Model of Compensation. Highlights • The effective elastic plate thickness of the Laxmi Ridge vary from 3 to 4 km. • The subsurface to surface load ratio is 0.8. • The ridge is underplated all along its length. • Geoid to topographic ratio over the ridge is negative (−1.98 m/km). • Laxmi Ridge is a stretched continental sliver intruded by volcanics. [ABSTRACT FROM AUTHOR]

The current local wavenumber methods for the interpretation of magnetic anomalies compute the locations of geological bodies by solving complex matrices. Presently, such methods require to know the structural index, which is a parameter that represents the source type. The structural index is hard to know in real data; consequently, the precision of current methods is low. We present the fast local wavenumber (FLW) method, and define the squared sum of the horizontal and vertical local wavenumbers as the cumulative local wavenumber. The FLW method is the linear combination of the umulative local wavenumberand other wavenumbers, and is used to compute the locations and structural index of the source without a priori information and matrix solution. We apply the FLW method to synthetic magnetic anomalies, and the results suggest that the FLW method is insensitive to background and oblique magnetization. Next, we apply the FLW method to real magnetic data to obtain the location and structural index of the source. [ABSTRACT FROM AUTHOR]

To study the magnetic signature of submarines and improve the performance of magnetic anomaly detectors in the antisubmarine warfare, the generation mechanism of the submarine magnetic field (SMF) is first introduced. Magnetic fields produced by submarines are classified into five major types by the cause and state of submarines. Besides, the prediction model of the SMF at low altitude is proposed. Based on the surface integral method, the continuation formula of the magnetic field is derived from the vector potential. According to the magnetic field of a real mockup, the distribution of the SMF is obtained by the continuation formula, and the data of the magnetic anomaly caused by submarines are produced at different heights. Then, the spatial signature of the magnetic anomaly is analyzed. The result of analysis shows that the magnetic anomaly of ferromagnetic submarines has evident characteristics. The distribution of the magnetic anomaly is spatially symmetrical, and the peak values of its components and total field occur in special positions. Furthermore, the signal strength of the magnetic anomaly is sufficiently large to be detected. So the identification of underwater magnetic target can be realized by the special magnetic signature. [ABSTRACT FROM PUBLISHER]

Forward modeling of planetary-scale magnetic anomalies due to induced crustal magnetization of Io is developed. The approach involves finite difference modeling of a temporally- and spatially-averaged steady state geotherm superimposed by the thermal evolution of an instantaneously emplaced volcanic pipe with and without an underlying magma chamber. A slight adjustment to previous studies results in a preferred steady state geotherm. The crustal magnetization is based on the calculated distribution of temperature, the strength of an idealized Jovian magnetic field, and a temperature-dependent susceptibility. Magnetite is assumed to be the dominant magnetic mineral. Synthetic satellite flyby data are generated along selected meridional swaths of Io’s surface, based on observed locations of volcanic centers, hotspots, and accumulations of ejected volcanic material. This work produces a 1-D geotherm which remains at approximately the surface temperature to within a few kilometers of the thermal lithosphere/mantle boundary. This solution shows little dependence on porosity due to the depth at which rapid temperature change occurs. These conclusions hold for largely varying mantle temperatures. Silicate volcanic centers cool to the temperature of sulfur eruptions rapidly and become indistinguishable from sulfur volcanism within 10,000 years. The magnetic anomaly due to temperature variation is smaller than detectable for nominal conditions. The modeling herein requires a flyby altitude of ∼25 km and a pipe radius of ∼640 m for detection, or, for a more reasonable flyby altitude of 100 km, a pipe radius of ∼6000 m. If a crustal anomaly is detected by future satellite missions, it would suggest different conditions at Io than modeled here. [ABSTRACT FROM AUTHOR]

A genetic algorithm (GA) is an artificial intelligence method used for optimization. We applied a GA to the inversion of magnetic anomalies over a thick dike. Inversion of nonlinear geophysical problems using a GA has advantages because it does not require model gradients or well-defined initial model parameters. The evolution process consists of selection, crossover, and mutation genetic operators that look for the best fit to the observed data and a solution consisting of plausible compact sources. The efficiency of a GA on both synthetic and real magnetic anomalies of dikes by estimating model parameters, such as depth to the top of the dike ( H), the half-width of the dike ( B), the distance from the origin to the reference point ( D), the dip of the thick dike ( δ), and the susceptibility contrast ( k), has been shown. For the synthetic anomaly case, it has been considered for both noise-free and noisy magnetic data. In the real case, the vertical magnetic anomaly from the Pima copper mine in Arizona, USA, and the vertical magnetic anomaly in the Bayburt-Sarıhan skarn zone in northeastern Turkey have been inverted and interpreted. We compared the estimated parameters with the results of conventional inversion methods used in previous studies. We can conclude that the GA method used in this study is a useful tool for evaluating magnetic anomalies for dike models. [ABSTRACT FROM AUTHOR]

The Tilt-depth method has been widely used to determinate the source depth of a magnetic anomaly. In the present study, we deduce similar Tilt-depth methods for both magnetic and gravity data based on the contact and sphere models and obtain the same equation for a gravity anomaly as that for a magnetic anomaly. The theoretical equations and the model tests show that the routine Tilt-depth method would result in unreliable depth estimation for deep sources. This is due to that the contact model is no longer valid for causative sources under the condition in which the depths of causative sources are significantly larger than their horizontal lengths. Accordingly, we suggest that the Tilt-depth derived from the contact model can be used to detect a shallow source, whereas the Tilt-depth derived from the sphere model can be used to detect a deep source. We propose a weighting method based on the estimated depths from both the contact model and the sphere model to estimate the depth for real data. The model tests suggest that the determined depths from the contact model and the sphere model are shallower and deeper, respectively, than the real depth, while the estimated depth from the proposed method is more close to the actual depth. In the application to the Weigang iron ore located in Jiangsu province, China, the routine Tilt-depth method results in −76% relative error, whereas the proposed method obtains the reliable depth estimation compared with the drill holes. In addition, the proposed method works well in the application for the Shijiaquan iron ore located in Shandong province, China. These results indicate that the proposed weighting equation is a general improvement. [ABSTRACT FROM AUTHOR]