Interpretation Of Potential Field Data Research Articles

Studying the theoretical basis and advantages and disadvantages of Logistic methods of the total horizontal Gradient

Edge detection is one of the most important steps in interpretation of magnetic and gravity data. In magnetic and gravity maps, it is difficult to distinguish adjacent sources due to their field superposition. Many different techniques have been used to determine the edges of sources. These techniques are based on vertical or horizontal gradients of magnetic and gravity data or combinations of them, and the edges of the geological structures are determined by maximum, minimum, or zero values in the output maps. One of the most popular techniques is the total horizontal gradient which is based on horizontal gradients of magnetic and gravity data. The capability of the total horizontal gradient technique in mapping the boundaries of deep bodies is very limited when competing with large-amplitude shallow bodies. Some enhanced modifications of the total horizontal gradient technique have been introduced to improve the boundary estimation results. These techniques are based on logistic functions and derivatives of the total horizontal gradient. In this study, we aim to estimate the effectiveness of the logistic filters of the total horizontal gradient. To obtain optimum results, these filters were tested on synthetic gravity and magnetic data and real magnetic data from the Zhurihe region (China). The findings show that the logistic filters can provide more accurate and sharper boundaries without false source edges than the total horizontal gradient. These techniques can determine the edges of shallow and deep structures at the same time. These results demonstrate that the logistic filters are useful tools for the qualitative interpretation of potential field data.

Stable iterative downward continuation of potential field based on Runge-Kutta method

Downward continuation is a useful transformation in the processing and interpretation of potential field data. However, this transformation is known for its inherent instability. In this paper, we proposed a stable iterative Runge-Kutta method for downward continuation that uses an average slope over the interval of continuation. Because of the truncation error, we combine the ideas of Runge-Kutta with the iterative downward continuation methods in a single method to improve the accuracy and the precision of the method. The presented method needs only the computation of the first order vertical derivatives (slope) over the whole interval of continuation using the Tikhonov regularization. To validate the efficiency of the proposed method, various tests were conducted on synthetic magnetic data as well as real aeromagnetic data. The obtained results clearly show the stability of our method for the downward continuation of potential field data.

Fault modeling around southern Anatolia using the aftershock sequence of the Kahramanmaraş earthquakes (Mw = 7.7 and Mw = 7.6) and an interpretation of potential field data

Fault modeling around southern Anatolia using the aftershock sequence of the Kahramanmaraş earthquakes (Mw = 7.7 and Mw = 7.6) and an interpretation of potential field data

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.

Automatic Interpretation of Potential Field Data Based on Euler Deconvolution with Linear Background

Euler deconvolution is a popular technique used for analyzing potential field data because it requires little prior information. However, the reliability of Euler solutions can be impacted by interference from adjacent field sources, or background fields. In this manuscript, we present an effective Euler deconvolution algorithm that accounts for linear background fields. Our algorithm, called improved finite-difference Euler deconvolution, builds upon the finite-difference method and is less susceptible to interference from nearby sources. We use this algorithm to achieve a joint estimation of the coefficients of the source coordinates, the structure index, and the linear background trend. Compared to Euler deconvolution methods based on differential similarity transformations, which also account for linear background fields, our method is easier to understand and implement programmatically and is faster. We tested our method using both 2D and 3D synthetic data, and the results indicate that our algorithm has better computational accuracy than the finite-difference algorithm and is comparable to the Euler deconvolution algorithm based on differential similarity transformations. In addition, our method was shown to be effective when tested on real data.

A geophysically constrained crustal element map of East Antarctica between Enderby Land and Princess Elizabeth Land

East Antarctica along with Greater India played a vital role in the accretion and breakup of the Indo-Antarctic landmasses during the supercontinents Nuna, Rodinia and Gondwana. Without geophysical potential field methods, interpreting the architecture of the ice-covered geological provinces of Antarctica is impossible. We present here a crustal element map of East Antarctica between Enderby Land and Princess Elizabeth Land (Indo-Antarctica tectonic element) using aerogeophysical data interpretation. The data reveal distinct anastomosing geophysical provinces that correlate with sparse geological data. Our crustal element map shows the Oygarden Province and the Northern and Southern Rayner provinces are arcuate belts that wrap around the Archean Napier Province. These provinces represent the remnants of an accretionary tectonic margin, which evolved between ca 1300 Ma and 900 Ma. The arcuate geometry of these Meso- to Neoproterozoic provinces formed during the collision with the Napier Province, which represents a microcontinent. This collision triggered widespread extension and ultra-high temperature metamorphism in the Northern and Southern Rayner provinces. The southernmost provinces include the Fisher Province, Lambert Province and a transition zone. The provinces are truncated by a suture zone with the Archean Ruker Province, following north-dipping subduction during the Meso- to Neoproterozoic. Our interpretation provides a template upon which to correlate geological provinces with the terranes on the conjugate eastern Indian margin. KEY POINTS An aeromagnetic interpretation is given for Enderby Land and Princess Elizabeth Land of East Antarctica. Napier Province is a microcontinent that collided with the Rayner Province during a ca 1000 Ma orogenic event. A new interpretation of potential field data suggests anastomosing provinces accreted as part of a collisional event. New structures/piercing points are identified at the Mawson Coast and in Kemp Land.

Structural interpretation of potential field data using the enhancement techniques: a case study

The enhancement techniques of potential field data are commonly used to detect the boundary locations of geological structures. There are many different techniques for estimating the source boundaries. Through synthetic examples and Bouguer data from the southern Red Sea, we have evaluated the performance of 15 enhancement techniques. The findings show that the tilt angle of horizontal gradient (TAHG) and fast sigmoid (FSED) techniques perform better than other techniques under almost all scenarios. Moreover, these two techniques can avoid producing false structures or connected structures as other techniques. The extracted lineaments from the TAHG and FSED were compared with surface faults of the study area. As a result, major differences are caused by rifting effect on the oceanic crust. The obtained results provide valuable information to better understand the structural features of the southern Red Sea and to introduce a more reliable structural interpretation.

Potential field data interpretation to detect the parameters of buried geometries by applying a nonlinear least-squares approach

Potential field data interpretation to detect the parameters of buried geometries by applying a nonlinear least-squares approach

An edge-assisted smooth method for potential field data

Abstract Edge detection is one of the most commonly used methods for the interpretation of potential field data, because it can highlight the horizontal inhomogeneous of underground geological bodies (faults, tectonic boundaries, etc.). A variety of edge detection methods have been reported in the literature, most of which are based on the combined transformation results of horizontal and vertical derivatives of the observations. Consequently, these edge detection methods are sensitive to noise. Therefore, noise reduction is desirable ahead of applying edge detection methods. However, the application of conventional filters smears discontinuities in the data to a certain extent, which would inevitably induce unfavourable influence on subsequent edge detection. To solve this problem, a novel edge-preserving smooth method for potential field data is proposed, which is based on the concept of guided filter developed for image processing. The new method substitutes each data point by a combination of a series of coefficients of linear functions. It was tested on synthetic model and real data, and the results showed that it can effectively smooth potential field data while preserving major structural and stratigraphic discontinuities. The obtained data from the new filter contain more obvious features of existing faults, which brings advantageous to further geological interpretations.

Structural signatures of the Amazonian Craton in eastern Colombia from gravity and magnetometry data interpretation

Geophysical interpretation of potential field data plays an important role in the integration of geological data. Estimation of density and magnetic susceptibility variations within the upper crust helps evaluating the continuity of geological structures in the field. In the present study we use gravity and magnetic data in NW Amazonian Craton in Colombia. Total horizontal gradient of the reduction to magnetic pole were used to delineate magnetic lineaments and domains showing four zones, each with its own features. Multiscale edge detection (worming) of the data help delineate upper crustal structures that we interpret as tectonic boundaries that correlate with the four zones identified. 3D density and magnetic susceptibility inversion showed high density and/or high magnetic susceptibility sources correlated with these crustal structures. Zone (1) is located south of the Guaviare River, with predominant NW-SE and NE-SW magnetic lineaments; zone (2), located from south of the Guaviare River to the north, present nearly E-W magnetic lineaments and a deep E-W edge interpreted as a possible shear zone parallel to Guaviare, Orinoco and Ventuari rivers; zone (3) from south of the Vichada River to the north, with NE-SW and NW-SE lineaments; N-S zone (4) cuts the zones (2) and (3), characterized by high density/magnetic susceptibility source bounded by N-S deep edges. A more complete tectonic evolution interpretation requires further work, but we speculate that the zone (4) could indicate an aborted rift/collision suture and that the zone (2) is indicative of a younger deformation event. Shear direction at (2) is not clear: geological maps show NEE-SWW right-lateral faulting, but geophysical anomalies suggest left-lateral displacement, highlighted by left dislocation of the Orinoco River. We also speculate that a N-S edge located at the SE of the area can be related with the Atabapo Belt and the limit of Ventuari-Tapajós and Rionegro geochronological provinces.

Contribution of gravity and aeromagnetic data to the structural modeling of the hidden faults in Guercif Basin, northeastern Morocco

The Guercif Basin of the northeastern Morocco is regarded as a particular sedimentary basin influenced by the tectonics of the Middle Atlas Fault Zone, the Rif orogenic belt and the stable eastern Meseta. Its faulting structures are poorly perceived on surface because of the thick recent sedimentary cover that overlies the Mesozoic-Paleozoic basement. The interpretation of potential field data shows relevant results in deciphering the basement structure of a complex sedimentary basin, such as the Guercif Basin. In order to understand the structural framework of this basin and to establish its subsurface structural map, gravity and magnetic data were processed using various edge detection techniques accomplished by an extensive geological data and seismic interpretations.A new subsurface structural map was established where many faults already recognized or supposed by traditional structural studies have been confirmed and new major ones by specifying their trends and depths have been emphasized. In addition, this new map demonstrates that the Guercif Basin is affected by several major faults elongated in three main trends: NE-SW, E-W and NW-SE, inherited from Variscan tectonics and reactivated in relation with atlasico-alpine tectonics.The established referential map reveals that the study area is subdivided into two different structural domains; a western one principally affected by NE-SW trending faults representing the northeastern extension of the Middle Atlas Fault Zone, and an eastern domain belonging to the stable eastern Meseta and characterized in general by large E-W trending faults. It allows us also to identify a sinistral fault zone in Tafrata area which we have labeled “Tafrata Fault Zone” and to define the continuity of the North Middle Atlas Fault (NMAF), the Central Middle Atlas Faults (CMAF) and the South Middle Atlas Fault (SMAF) which presents very likely the limit between the two identified domains. The elaborated map will be a useful document for all future petroleum explorations or hydrogeological investigations.

Phân tích dữ liệu từ vùng vĩ độ thấp sử dụng phép biến đổi wavelet liên tục hai chiều

Nowadays, the continuous wavelet transform has been applying for interpretation of potential field data to detect accurately the location for the anomaly sources and their properties. For magnetic data at low latitude areas such as the Mekong Delta (latitudes 11,07o), both of the magnetization and ambient field are not directed vertically, making magnetic anomalies antisymmetrical and often skewed to the location of the sources. So it is significantly problematic to interpret these anomalies. In this paper, two-dimensional continuous wavelet transform (2-D CWT), using Farshad-Sailhac complex wavelet function is studied and applied for reducing the magnetic anomaly to a symmetrical one - this located on the source of the anomaly, and then determining the position of the center of the object causing anomalies by wavelet transform modulus maxima (WTMM) method, to enhance the quality of magnetic data interpretation in this area. Furthermore, to determine the anomaly sources ’s properties effectively, the relationship between the source depth and the scale corresponding the maximum point of the wavelet transform coefficients as well as the equation for estimation the one size have been formed. After verifying the reliability of the proposed method on the modeling data, a process for the location of the magnetic anomalies at low latitude areas using the wavelet transform is set up, and then application for analyzing the magnetic data in the Mekong Delta.

Multi-Scale Edge Detection Method for Potential Field Data Based on Two-Dimensional Variation Mode Decomposition and Mathematical Morphology

Using observational data to determine the edges of the sources is an important task in the interpretation of potential field data. Extracting the edges of deep and shallow bodies effectively is the key to correctly understanding the underground structure. Based on the good multi-scale decomposition ability of two-dimensional variational mode decomposition (2D-VMD) and the outstanding shape analysis capability of mathematical morphology (MM), a new multi-scale edge detection method for potential field data is proposed. We propose using the variance of this morphological filter as a basis for selecting the optimal structural element (SE) scale. By establishing theoretical models and comparing the results of our method with those of traditional edge detection methods, the proposed method is shown to be effective at detecting edges within potential field data. Taking the Hanmiao area of Chifeng city, Inner Mongolia, China, as an example, 1:50000 aeromagnetic data are processed and analysed by this method. The physical properties of the rocks in the study area are also discussed. The results of theoretical calculations and real data processing show that this method can accurately extract the edges of the sources at different scales. And the real data processing results show that this method is suitable for the identification of structural faults.

A novel method for computing the vertical gradients of the potential field: Application to downward continuation

Summary Downward continuation is a very useful technique in the interpretation of potential field data. It would enhance the short wavelength of the gravity anomalies or accentuate the details of the source distribution. Taylor series expansion method has been proposed to be one of the best downward continued methods. However, the method using high-order vertical derivatives leads to low accuracy and instability results in many cases. In this paper, we propose a new method using a combination of Taylor series expansion and upward continuation for computing vertical derivatives. This method has been tested on the gravitational anomaly of infinite horizontal cylinder in both cases with and without random noise for higher accurate and stable than Hilbert transform method and Laplace equation method, especially in the case of noise input data. This vertical derivative method is applied successfully to calculate the downward continuation according to Taylor series expansion method. The downward continuation is also tested on both complex synthetic models and real data in the East Vietnam Sea (South China Sea). The results reveal that by calculating this new vertical derivative, the downward continuation method gave higher accurate and stable than the previous downward continuation methods.

Edge enhancement of potential field data using the logistic function and the total horizontal gradient

Locating the edges of anomalous bodies provides a fundamental tool in the geologic interpretation of potential field data. This paper compares the effectiveness of the commonly used edge detection methods such as the total horizontal gradient, analytic signal, tilt angle, theta map and their modified versions in terms of their accuracy on the determination of edges of source bodies. This paper also introduces an edge detector method for the enhancement of potential field anomalies, which is based on the logistic function of the total horizontal gradient. The new method is tested on synthetic data calculated using 3 models, and also on real magnetic and gravity data from Vietnam. The effectiveness of the method is evaluated by comparing the results with those of other popular methods. These results demonstrate that the method is a useful tool for the qualitative interpretation of potential field data.

STDR: A Novel Approach for Enhancing and Edge Detection of Potential Field Data

Edge detection is one of the most important steps in the map interpretation of potential field data. In such a dataset, it is difficult to distinguish adjacent anomalous sources due to their field superposition. In particular, the presence of overlain shallow and deep magnetic/gravity sources leads to strong and weak anomalies. In this paper, we present an improved filter, STDR, which utilises the ratio of the second-order vertical derivative to the second-order total horizontal derivative at the tilt angle equation. The maximum and minimum values of this filter delineate the positive and negative anomalies, respectively. This novel filtering approach normalises the intensity of strong and weak anomalies, as well as anomalies with different depths and properties. Moreover, to better illustrate the edges, its total horizontal derivative (THD_STDR) is also used. For positive and negative anomalies, the maximum value of the THD_STDR filter shows the edges of the anomalies. The potentiality of the proposed method is examined through both synthetic and real case scenarios and the results are compared with a number of existing edge detector filters, namely TDR, THD_TDR, Theta and TDX. Due to substantial improvements in the filtering, STDR and its total horizontal derivative allow for more accurate estimation of anomaly edges in comparison with the other filtering techniques. As a consequence, the interpretation of the potential field data is more feasible using the STDR filtering method.

The utility of shift-sampling method to enhance the precision of the calculation of gravity effect in frequency domain ·

20 and 30 graviy inversion in frequency domain was widely applied in the interpretation of potential field data, because, unlike the interpretation in space domain, it permits to reduce significaltly computer time. Precision of the interpretation in frequency domain is dependent upon the precision of the transformation between the space and frequency domain. This precision can be improved by the shift - sampling method, which is based on the discrete Fourier transform (OFT) deviation equation.In this paper, shift sampling method is applied to estimate it·s utilization in the calculation gravity effect on both 20 and 30 mathematical models, in which an infinite horizontal cylinder is used as 20 model and a sedimentary basin approximated by vertical rectangular prisms is used as 30 model.With application of shift- sampling method, precision of the calculation gravity effect in frequency domain is enhanced. For both models, root-meansquare error reduced by several tens times. This makes gravity anomaly calculated in frequency domain almost exactly in consistence with the gravity anomaly calculated in space domain. Therefore thismethod helps in the solving the problem of gravity inversion in consistence frequency domain.

2D potential theory using complex algebra: New equations and visualization for the interpretation of potential field data

The shape of an anomaly (magnetic or gravity) along a profile provides information on the geometry, horizontal location, depth, and magnetization of the source. For a 2D source, the horizontal location, depth, and geometry of a source are determined through the analysis of the curve of the analytic signal. However, the amplitude of the analytic signal is independent of the dips of the structure, the apparent inclination of magnetization, and the regional magnetic field. To better characterize the parameters of the source, we have developed a new approach for studying 2D potential field equations using complex algebra. Complex equations for different geometries of the sources are obtained for gravity and magnetic anomalies in the spatial and spectral domains. In the spatial domain, these new equations are compact and correspond to logarithmic or power functions with a negative integer exponent. We found that modifying the shape of the source changes the exponent of the power function, which is equivalent to differentiation or integration. We developed anomaly profiles using plots in the complex plane, which is called mapping. The obtained complex curves are loops passing through the origin of the plane. The shape of these loops depends only on the geometry and not on the horizontal location of the source. For source geometries defined by a single point, the loop shape is also independent of the source depth. The orientation of the curves in the complex plane is related to the order of differentiation or integration, the geometry and dips of the structures, and the apparent inclination of magnetization and of the regional magnetic field. The application of these equations and mapping on total field magnetic anomalies across a magmatic dike in Norway shows coherent results, allowing us to determine the geometry and the apparent inclination of magnetization.

Public domain satellite gravity inversion offshore Somalia combining layered-Earth and voxel based modelling

At the end of 2016, Spectrum Geo released two long offset seismic reflection profiles across the Somalian rifted margin, in the Juba Lamu and Obbia basins respectively – part of two larger 2D surveys acquired in 2014 and 2015/16 (Stanca et al., 2016; Figure 1). In frontier areas, potential field data interpretation, in particular public domain satellite-derived gravity, can play a key role in the early stages of exploration by identifying basement structure, sediment thickness, and the continental-oceanic crust transition (COT) or continental-oceanic boundary (COB), and hence indirectly contribute to the understanding of thermal history and the hydrocarbon system. This is particularly relevant over the Somalia margin, where geophysical surveys have been extremely sparse until very recent years. A high-gradient in the gravity is often used as a marker of the COB along passive margins (see Pawlowski (2008) for a review), expressing laterally contrasting physical properties between the continental and oceanic crusts. However, at magma-poor rifted margins, such as the Somalia margin, the lithosphere undergoes a progressive thinning/stretching process and the transition between unaltered continental crust and oceanic crust becomes gradual (Manatschal, 2004). Crustal hyper-extension, serpentinization, embrittlement, and exhumation of mantle peridotites can precede accretion of true oceanic crust, which in turn can blur the simple transitional model between a dense and highly magnetized oceanic crust and a weakly magnetized and lighter continental crust. Along a magma-poor margin, analysis of potential field data can distinguish the different rifting domains and quantify crustal thinning (Stanton et al., 2016; Cowie et al., 2015). In offshore Kenya and Somalia, the image is further complicated by thick sedimentary cover.

Edge detection in potential filed using the correlation coefficients between the average and standard deviation of vertical derivatives

Edge detection is an essential task in the interpretation of potential field data. Many existing edge detection methods are the functions composed by the horizontal derivative and vertical derivative of potential field data. The edges recognized by those methods are bigger than the true edges and when the depths of the geological bodies are different, the edges will be detected fuzzy and difficult to identify the edges accurately. In this paper, we present a new method to delineate the edges of the sources, which is based on the correlation coefficients between the average and standard deviation of vertical derivatives in a sliding window. The algorithm of this method is very simple. The zero value of the correlation coefficients is used to delineate the geological edges. It's clear to see the edges with the zero contours which will lead to continuous and clear detected edges and the method shows the edges more precisely. Moreover, the anomalies in different depths can be detected in the same degree and are insensitive to noise. The measure is initially applied on the synthetic gravity and magnetic data. The tests of theoretical models indicate that the new method could detect the edges of models in different depths and the position is in good accordance with the models' edges. Finally, this method is applied to gravity data from a portion of Vientiane Basin, Laos. As a result, the method is helpful in recognizing geologic fractures clearly. Moreover, it shows more geologic details with smaller window size and gives superior results with higher quality data.