Total Magnetic Field Anomalies Research Articles

2.5D magnetization vector inversion of vector magnetic data

The remanent magnetization vector records the earth’s magnetic field at the time of the formation process of magnetized geologic units. Recovering the magnetization vector from magnetic data can provide extra information regarding the source properties to differentiate geologic units and reveal thermal evolution or tectonic history. To provide this information, the magnetization vector inversion (MVI) method has been used to invert for the magnetization vector. The MVI usually works with the total-field magnetic anomaly magnitude ([Formula: see text]). The magnitude is an approximation of the projection of the magnetic anomaly vector onto the normal geomagnetic field. For highly magnetic sources, the approximation error of [Formula: see text] cannot be ignored. However, this approximation error can be avoided by using measured vector magnetic data. To reduce the severe ambiguity of 3D MVI, specific constraints based on extra prior information are usually used. For 2D or 2.5D cases, MVI only inverts for magnitude and inclination of the magnetization, which encounters less ambiguity than that of the 3D case. We have developed a 2.5D MVI approach using vector magnetic data. To reduce the divergent and smooth trends in magnetization vectors recovered by MVI in the Cartesian framework, we make use of a focusing constraint method to improve the imaging. The inversion results of synthetic data indicate that the method is able to recover magnetization magnitude and inclinations close to the true values and is fairly robust to inappropriate choice of the profile location and heading. Finally, the method is applied to the measured airborne vector magnetic data from the Qixin area of the East Tianshan Mountains in China. The distributions and directions of magnetization of the mafic-ultramafic rocks and linear structures are revealed, which provides the information for distinguishing geologic units and geologic differentiation.

New high resolution aeromagnetic anomaly map of Türkiye and its various derivative-based maps

Since Türkiye's territory is mostly mountainous and forested, earth science studies in these areas have not been completed at an adequate level and with a satisfying resolution. However, due to the long time and cost of collecting measurements from land in large- and medium-scale studies and due to the inability to collect measurements in regular grid intervals in large-scale studies to be carried out on land, an airborne geophysical survey project was conducted in order to collect high-resolution magnetic and radiometric country-scale data. Total magnetic field and radiometry data were collected from the air between 2017 and 2022 within the scope of the country-wide Airborne Geophysics Surveys Project. The data collection flights were carried out in such a way as to follow the topography from an altitude of about 200 m above the ground. The flights were carried out considering the regular geometry of the flight profile and the general geological and tectonic structure of Türkiye in the direction of N-S with one-kilometer profile intervals. A total field magnetic anomaly map was obtained after applying the diurnal, tie line leveling, IGRF (model 2020), and differential reduction to magnetic pole (DRTP) corrections to the magnetic data. For the scope of this study, the total field magnetic anomaly and the regional total field magnetic anomaly maps were presented along with the structural boundary maps (tilt angle (TA), the total horizontal derivative (THDR) and the analytical signal (AS)) derived from these maps. During another stage of the study, the general tectonic structure of Türkiye and structural boundaries obtained from derivative-based maps (AS, TA, and THDR) were compared. General geophysical interpretation was also performed with magnetic-anomaly and derivative-based maps for the three regions characterized by high magnetic anomalies.

Fast 3-D Magnetic Anomaly Forward Modeling Based on Integral Equation

Efficient and accurate 3D numerical modelling of total field magnetic anomaly is a key problem that restricts the 3D fast inversion imaging and geological interpretation of large-scale magnetic data. To address this problem, we develop a fast numerical modelling method for 3D magnetic anomaly based on integral equation. First, we derive a new analytical expression for prismatic total field magnetic anomaly, which has the advantages of compact structure and low computational cost. Then, we take advantage of the Toeplitz property of the kernel matrix when the grid is uniformly discretized in the horizontal directions to reduce the redundant computation and memory requirement without losing accuracy. In addition, the grid discretization in the vertical direction is flexible and can be finer at a shallower depth and coarser at a deeper depth, taking into account accuracy and efficiency. The 2D FFT is used to achieve fast discrete convolution of the kernel matrix and magnetic susceptibility, which greatly improves the efficiency of the discrete convolution. In the numerical examples, a cube model is designed to verify the correctness of this method. The results demonstrate that the computation time of our algorithm is reduced by 1~2 orders of magnitude, and the memory requirement is decreased by approximately 1 order of magnitude compared with the conventional fast magnetic anomaly numerical modelling method based on BTTB matrix, while achieving the same accuracy. Finally, the applicability of our algorithm is tested by calculating the terrain effect on an airborne magnetic data built in a real complex topography model.

Calculation of normalized source strength using second derivatives of the vertical integral of total-field magnetic anomaly

Normalized source strength (NSS) is often used to interpret remanence data owing to its low sensitivity to the direction of magnetization. However, calculations of NSS are unstable at low latitudes. Therefore, we have developed a new parameter called modified NSS (MNSS), in which NSS is calculated using the second derivatives of the vertical integration of a total-field magnetic anomaly, rather than using magnetic field components. This approach helps to stabilize the NSS calculation. MNSS is slightly dependent on the magnetization direction, but the calculation of the latter does not require geomagnetic field direction information, meaning that MNSS calculations are convenient and very stable even at very low latitudes or over the equator. Here, we develop test models and a field-based case study to illustrate the features and advantages of MNSS.

A new perspective on the continent–ocean boundary of Palawan continental block identified with geophysical data

The location of the Continent–ocean boundary (COB) between the Palawan continent block (PCB) and the central oceanic basin remains controversial. There are more than 100 km difference among the scholars' view about the specific positions of the COB. To obtain a more reasonable location of the COB in the PCB, a comprehensive interpretation was conducted based on new shipborne geophysical data, including bathymetry, gravity, magnetic and reflection seismic data. In particular, upward continuation was applied to the new stern-towing magnetic data, and analytical signal analysis (ASA) processing was adopted for the total field magnetic anomalies, including both the public and stern-towing magnetic data. The most reasonable COB of PCB is just identified with the geophysical data based on the comprehensive structures' anomalies, such as the foot of massif slope and the magmatic volcanoes in topographic data, and the gentle gradient of the free-air and Bouguer gravity anomalies, and the clear dividing boundary in magnetic ASA sharp anomaly, and the seismic profiles structure's display in the Continent–ocean transition (COT). Meanwhile, structural modeling along the seismic profiles are used to constrained the identification. The refined convex–concave's COB is distributed at the seaward limit of the continental crust along the foot of northwest Palawan slope with a hyper-extended thinner crust, seaward-dipping listric faults, and is reasonably located between the extensive thinned continental crust and expansive subducting oceanic crust.

There is more Wrangellia — magnetic characterization of southern Alaska crust

In southern Alaska, Wrangellia-type magnetic crustal character extends from the Talkeetna Mountains southwest through the Alaska Range to the Bristol Bay region. Magnetic data analyses in the Talkeetna Mountains showed that there are mid-crustal differences in the magnetic properties of Wrangellia and the Peninsular terrane. After converting total field magnetic anomaly data to magnetic potential, we applied Fourier filtering techniques to remove magnetic responses from deep and shallow sources. The resulting mid-crustal magnetic characterization delineates the regional magnetic potential domains that correspond to the Wrangellia and Peninsular terranes throughout southern Alaska. These magnetic potential domains show that Wrangellia-type crust extends southwest to the Iliamna Lake region and that it overlaps the mapped Peninsular terrane. Upon reconsidering geologic ties between Wrangellia, Peninsular, and Alexander terranes, we conclude that Peninsular terrane is part of what we here call Western Wrangellia. Western Wrangellia contains the Lower Jurassic Talkeetna volcanic arc and is similar to Wrangellia of the Vancouver Island area, Canada (Southern Wrangellia), which contains the Lower Jurassic Bonanza volcanic arc. Others have previously made this correlation and proposed that the Talkeetna arc-bearing part of southern Alaska was displaced from the Bonanza arc-bearing part of Canada. We generally agree and propose that about 1000 km of dextral displacement along ancestral Border Ranges fault segments and other faults of south-central Alaska separated Western Wrangellia from Southern Wrangellia. We think this displacement was mostly in the Late Jurassic and earliest Cretaceous, perhaps between about 160 and 130 Ma.

Using airborne vector magnetic data to calculate the projection of the magnetic anomaly vector onto a normal geomagnetic field

The total-field magnetic anomaly [Formula: see text] is an approximation of the projection [Formula: see text] of the magnetic anomaly vector [Formula: see text] onto the normal geomagnetic field [Formula: see text]. However, for highly magnetic sources, the approximation error of [Formula: see text] cannot be ignored. To reduce the error, we have developed a method for calculating [Formula: see text] by using airborne vector magnetic data based on the vector relationship of geomagnetic field [Formula: see text]. The calculation uses the magnitude of the vectors [Formula: see text], [Formula: see text], and [Formula: see text] through a simple approach. To ensure that each magnitude has the same level, we normalize the magnitude of [Formula: see text] using the total-field magnetic data measured by the scalar magnetic sensor. The method is applied to the measured airborne vector magnetic data at the Qixin area of the East Tianshan Mountains in China. The results indicate that the calculated [Formula: see text] has high precision and can distinguish the approximation error of approximately 0.1 nT. We also analyze the characteristics of the approximation error that are caused by the effects of different total magnetization inclinations. These error characteristics are used to predict the total magnetization inclination of a 2D magnetic source based on the measured airborne vector magnetic data.

Regional integration and 3D modeling of airborne geophysical data: Map of Geophysical Anomalies of Colombia for mineral resources, 2020 version

The Map of Geophysical Anomalies of Colombia for mineral resources, MAGC 2020 version compiles the geophysical information acquired, processed and interpreted by the Servicio Geológico Colombiano (SGC) since 2013. This information was collected via airborne platforms (aircrafts) using magnetometry and gamma spectrometry. This version covers approximately 547 960 km2 of the national territory in the Andean (North and Central), Eastern (Eastern Plains and Amazon) and Caribbean zones (Perijá mountain range). This information consists of 17 blocks of geoscientific interest, covered by flight lines separated by 500 and 1000m, for a total of more than 907 566 linear km of airborne information, acquired at a nominal altitude of 100 m above the ground, with a sampling resolution that was not previously available at this scale and coverage. This document presents the methodology for compiling, processing and representing the thematic coverage included in MAGC 2020: Map of Total field magnetic anomaly (TFMA), Map of the analytic signal (AS) and radiometric ternary map of the distribution of the relative concentrations of uranium, thorium and potassium. Furthermore, the work identifies 1079 magnetometric anomalies of interest, which were subsequently analyzed and modeled in the Map of magnetic sources modeled from magnetization vector inversion, which contains a total of 1297 magnetic bodies interpreted from these anomalies. Integration of available geological and metallogenic information with each of these bodies allow the suggestion of possible geological sources and possible exploration targets. The objectives of this study were to generate and integrate geophysical information to identify new areas of interest with regards to potential mineral resources, and to generate new geoscientific knowledge about Colombia for land-use planning.

High-resolution total field magnetic anomaly maps of Lake İznik (NW Turkey): assessment of faults which play important roles in tectonics of the lake

High-resolution total field magnetic anomaly maps of Lake İznik (NW Turkey): assessment of faults which play important roles in tectonics of the lake

Inversion of high-amplitude magnetic total field anomaly: an application to the Mengku iron-ore deposit, northwest China

In magnetic prospecting, the total field anomaly formula that represents the projection of the magnetic anomaly vector on the geomagnetic field is widely used because it simplifies the calculation of forward modelling and inversion of magnetic data. However, the projection anomaly yields errors relative to the true observed magnetic anomaly, especially for high-amplitude magnetic anomalies such as in iron orebody and unexploded ordnance prospecting. In this study, we analyse the difference between the projection anomaly and observed modulus difference anomaly with physical parameters, and propose to directly invert for the modulus difference anomaly by constructing a nonlinear matrix equation between the model corrections and data corrections. The inversion is then implemented using a preconditioned conjugate gradient algorithm. Synthetic and field magnetic data were used to test the inversion method. Comparison of the two types of total field anomalies shows that the error of the projection anomaly increased with increasing total-field magnetic anomaly. When the total-field magnetic anomaly was < 5,000 nT, the difference between the projection anomaly and modulus difference anomaly results can be ignored. For high-amplitude magnetic anomalies, the modulus difference anomaly inversion produced more accurate representations of both the shape and location of the magnetic sources.

Application of magnetic method for mapping buried structures around archaeological site of Masjid Tuha Indrapuri

Magnetic gradiometer survey has been conducted on the yard of the archaeological site of Masjid Tuha Indrapuri, Aceh Besar Regency, Aceh Province. The site is one of the oldest mosques erected during the Aceh Sultanate period. Magnetic method was applied for mapping archaeological structures buried beneath the surface. Total magnetic field data were measured using Proton Precession Magnetometer with grid spacing of 2 meters between stations covering the entire area of the site. Diurnal and international geomagnetic reference field data were corrected to the measured data in order to calculate total magnetic field anomalies that were influenced by the buried magnetic objects. The total magnetic field anomalies distribution shows two elongated structures with U-shaped patterns surrounding the mosque. The patterns are also revealed in reduction to the pole and derivative vertical filters of the total field anomaly data. The anomaly patterns are considered a response from the rest of the buried fences that were built around the mosque in the past.

Combined geophysical investigations of the characteristics of a regional fault zone for groundwater development in a basement complex terrain of South-west Nigeria

This paper presents the results of an integrated electrical resistivity and magnetic survey of a strike slip fault in a basement complex terrain with poor well/borehole yield. It aims to characterize the fault zone and determine its geometry, width and depth extent and attitude that will enable an assessment of its prospectivity for groundwater development. The magnetic profiles imaged a fault block characterized by a low (negative) total field magnetic anomaly with a width extent ranging from 112 to 150 m, a depth extent in excess of 150 m and a near vertical disposition. The resistivity structures delineate low resistivity near vertical discontinuities within the high resistivity fresh basement host rock that correlate across the five traverses investigated. The north-western edge of the magnetic fault block and the resistivity anomalous zone correlates with the geo-referenced strike slip fault. The width of the low resistivity zone ranges from 75 to 125 m with depth extent in excess of 150 m. Four subsurface geologic/geoelectric layers were delineated. These include a relatively thin topsoil underlain by a clay/sandy clay weathered basement; a partly weathered/fractured basement column and a basal fresh basement with depth to rock head of 1.6–15.0 m. A zone with thick column (up to 117 m) of partly weathered/fractured basement correlates across the traverses and significantly with the anomalous magnetic and resistivity zones. The study concludes that the thicker region of partly weathered/fractured basement column within the fault zone which is likely to have enhanced permeability and storage capacities has potential for sustainable groundwater development. It also demonstrates the effectiveness of integrated 1D and 2D electrical resistivity imaging and magnetic profiling in structure (fault) identification, characterization, subsurface sequence delineation and groundwater potential assessment in a typical basement complex environment.

Interpretation of the Magnetic Measurements of the Swarm-A Satellite over Central Europe

Our paper discusses the determination of total magnetic field anomalies derived from the Swarm-A satellite data; one of two low orbiting satellites of the three Swarm formations. This procedure requires several modifications. The first step is the conversion of the measured CDF data to the ASCII format. This step is followed for the selection of the data with K_p index ≤ 1₊. The anomalies are determined by the removal of the IGRF from the resulting satellite data. There are two Swarm-A data sets descending (6000) orbits and ascending (5688) orbits. For our study the descending orbits were used. The calculations next step is to difference of the two-dimensional linear field Figure 3 fitted to the Swarm-A anomalies and the anomalies given in Figure 2. These anomalies are filtered by Gaussian low-pass filter. The last step of the corrections is the remove the direct component, zero spatial frequency, from the descending orbits. The anomalies and their vertical gradients are qualitatively interpreted over Central Europe and the Pannonian Basin.

An AI approach to automated magnetic formation mapping beneath cover

SummaryMost regional scale magnetic maps are dominated by the magnetic characteristics of steeply dipping basement units truncated by an unconformity surface. It is easy to demonstrate that 80 to 90% of each total field magnetic anomaly is contributed by this intersecting surface. We approach this problem by mapping the boundaries between contrasting magnetic units along each line in the magnetic survey using the full precision of the line data and 3D information from the magnetic gradient tensor. Additionally, we derive the azimuth of each boundary, depth to the unconformity and magnetic properties of the anomalous units. The segments are overlain on any image such as existing geological maps, satellite imagery, gravity or magnetic imagery to provide a new geological interpretation concept. This method provides a new way to interpret new and old magnetic surveys.Eigenvector analysis of the magnetic tensor and normalised source strength (NSS) are combined with an artificial intelligence (AI) approach to estimate the basement properties. The method is applied to full tensor magnetic survey data or a grid of the total magnetic intensity data is processed using FFT transformations to derive the magnetic gradient tensor. These data are used as input to the pre-trained AI process for calculation of depth, width, azimuth, magnetic susceptibility and magnetisation direction. The rock properties and depth information can be used for 3D visualisation of the unconformity and 2D mapping of the magnetic lithology of the unconformity surface.

Mapping of archaeological structure along east-coast of Aceh Besar District, Indonesia based on total magnetic field anomalies

The coast of Aceh along the northern tip of Sumatra had an important role since the beginning of the first millennium AD. The area was used as a transit point for the maritime silk road of the gate of the Malacca Strait. Many old settlements and ancient fortresses were found on the area. One of them is Indrapatra fortress. At present, the Indrapatra fortress has been slowly damaged by weathering and was also hit by disasters. Parts of the main building is still intact, while the other parts have been damaged and buried by sand deposits. In order to preserve the building, some actions need to be taken such as re-mapping the existence buildings and the buried parts as well. For this reason, a geomagnetic survey has been conducted to delineate the remains of the building at the subsurface. Data of total magnetic field intensity were acquired in an area of 31,255 m2 with a grid of 3 meters for each station so that the measurement covered the whole area of the target site. Total magnetic field anomalies were calculated using diurnal and International Geomagnetic Reference Field corrections. The obtained anomalies represent magnetic objects (archaeological structures) which buried beneath the surface. To obtain a more detailed form of anomalies several transformations, such as analytic signals, tilt derivatives, and horizontal derivatives were applied. The results of the transformations show several circular and elongated anomalies. The circular forms of anomalies are considered as buried wells, and the elongated forms are considered as channels which presumed connected the buildings in the area. The data showed that there are also foundations of the buildings made of stone structures cemented with lime plats.

Transformation from total-field magnetic anomaly to the projection of the anomalous vector onto the normal geomagnetic field based on an optimization method

The total-field magnetic anomaly [Formula: see text] is approximated as the component [Formula: see text] of the anomalous vector [Formula: see text] along the direction of the normal geomagnetic field. It is widely used in magnetic data processing and interpretation practices as a routine if [Formula: see text] is relatively small. But in highly magnetic environments, the distinction between [Formula: see text] and [Formula: see text] is often too large to be ignored. We carefully investigate the difference between [Formula: see text] and [Formula: see text] and find that it will increase rapidly in the trend of the quadratic function as [Formula: see text] strengthens. We also test the effects of approximation on the component transformation and reduction to the pole on a synthetic single-sphere model. As expected, the error caused by inaccurate information will propagate into subsequent data processing procedures and adversely affect the results. Therefore, we have developed an optimization strategy based on the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm to transform the total-field anomaly into [Formula: see text]. First, we have constructed an objective function after transforming [Formula: see text] into [Formula: see text] through the component transformation in the frequency domain. Then, using [Formula: see text] as the initial value of [Formula: see text], [Formula: see text] is calculated iteratively by the L-BFGS algorithm. To test the validity of the optimization algorithm, [Formula: see text] is transformed for noise-free and noise-corrupted models and models with a background field. The synthetics indicate that the transformed [Formula: see text] is almost the same as the model [Formula: see text], whose maximum error is approximately one-hundredth (30 nT) of the difference (8000 nT) between the modeled [Formula: see text] and [Formula: see text]. The synthetics and field data example from the Yangshan Iron Mine, Fujian Province, southern China, also indicate that the data transformation and forward-modeling results can benefit from the direct use of transformed [Formula: see text] instead of [Formula: see text].

Magnetic Anomalies of Submarine Pipeline Based on Theoretical Calculation and Actual Measurement

Marine magnetic method is widely used for detecting and locating the submarine pipeline. In this paper, the theoretical calculation model of total-field magnetic anomalies (TMAs) of submarine pipeline was derived based on Poisson’s equation. Taking a submarine gas pipeline for example, the TMA theoretical calculation and the verification sea test were carried out. Based on the calculation, the influences that the geomagnetic parameters, pipeline parameters, and measuring plane height had on the TMA characteristics of pipeline were analyzed. The TMA shape changed slightly with geomagnetic declination ${D}$ and was significantly influenced by the azimuth $\theta $ of the pipeline. The corresponded location of the pipeline on the TMA profile varied with ${D}$ seemed to be symmetrical with ${D} = 0^\circ $ as the center, but within 1.0 m, and changed greatly with $\theta $ with an offset distance of upping to 4.4 m. The TMA amplitude was linearly positively correlated with geomagnetic intensity ${T} _{0}$ , quadratic difference of outer and inner diameters of pipeline ${d} _{1}^{2}$ – ${d} _{2}^{2}$ , and susceptibility $\kappa $ , respectively, and was inversely proportional to the square of measuring plane height ${R}$ , and changed greatly with ${D}$ , ${I}$ , and $\theta $ but without obvious correlation. The TMA width changed greatly with ${I}$ and $\theta $ , respectively, but without obvious correlation, and was approximately positively correlated with R. On the TMA profile that was perpendicular to the pipeline, there would be an obvious “pulse” anomaly on the smooth profile, and the location of pipeline corresponded a specific point near the TMA maximum point depending on ${D}$ and $\theta $ , so that the accurate location of the pipeline needed to be corrected according to these two parameters, not just the TMA maximum point.

Magnetometry and ground penetrating radar in application to mapping of polygonal wedge ice of yedoma complex

Paper is dedicated to geophysical mapping of polygonal wedge ice. Magnetometric and ground penetrating radar surveys were implemented on a small area of Yedoma ice complex on Kurungnakh island in Lena river delta. Such deposits are widely spread on a huge areas of Siberia and Alaska. The study was conducted near the thermoerosional gully, which propagates along the most thick ice wedges. Polygonal pattern is observable on high-resolution aerial imagery and digital elevation model - this data was used during the interpreting of obtained results. Study area (40×50 m) was covered with highresolution magnetic survey at the elevation of 2 m with 2×2 m step and with ground penetrating radar survey along profiles with 1 m distance between the profiles. Map of total magnetic field anomalies allow to determine the ice wedges of Yedoma ice complex distinctly. Difference between maximum positive (polygons centers) and negative (ice wedges) anomalies reaches 6 nT (error of the survey is 0,3 nT). Beyond that smaller ice wedges which penetrate the ice wedges of Yedoma complex are also observable in magnetic field. Basing on ground penetrating radar data an amplitude slice of at 3,5 m depth was built. Yedoma ice wedges are observable at depth of 3–4 m. Ground penetrating radar data is quite noisy due to surface inhomogeneity (puddles, knolls, etc.). Results of the surveys were compared in the light of practical application of the methods for above mentioned goal. Magnetometric method appears as more efficient than ground penetrating radar survey: it does not require a contact with the surface and more rapid, it is more sensitive as the case stands. Ground penetrating radar method may have advantages in the case of natural (magnetic storm, high-magnetized overlaying deposits) and anthropogenic (metal constructions — pipelines, ETL) noise.

Marine Geophysical Investigation of the Chain Fracture Zone in the Equatorial Atlantic From the PI-LAB Experiment.

The Chain Fracture Zone is a 300‐km‐long transform fault that offsets the Mid‐Atlantic Ridge. We analyzed new multibeam bathymetry, backscatter, gravity, and magnetic data with 100% multibeam bathymetric data over the active transform valley and adjacent spreading segments as part of the Passive Imaging of the Lithosphere Asthenosphere Boundary (PI‐LAB) Experiment. Analyses of these data sets allow us to determine the history and mode of crustal formation and the tectonic evolution of the transform system and adjacent ridges over the past 20 Myr. We model the total field magnetic anomaly to determine the age of the crust along the northern ridge segment to better establish the timing of the variations in the seafloor fabric and the tectonic‐magmatic history of the region. Within the active transform fault zone, we observe four distinct positive flower structures with several en échelon fault scarps visible in the backscatter data. We find up to −10 mGal residual Mantle Bouguer Anomaly in the region of the largest positive flower structure within the transform zone suggesting crustal thickening relative to the crustal thinning typically observed in fracture zones in the Atlantic. The extensional/compressional features observed in the Chain Transform are less pronounced than those observed further north in the Vema, St. Paul, and Romanche and may be due to local ridge segment adjustments.

Manyetize Olmuş Jeolojik Yapıların Model Parametrelerinin Belirlenebilmesi için Gelişmiş Lokal Dalga Sayısı Tekniğinin Toplam Alan Manyetik Anomalilere Uygulanması

In this study, enhanced local wave number (ELWN) technique is presented to compute some model parameters of isolated and magnetized geological structures such as horizontal position (exact origin), depth and source geometry using the total field magnetic anomalies (TMAs). The technique uses analytical signal amplitude (ASA) and first- and second-degree horizontal and vertical derivatives of observed TMAs, and then simply computes the model parameters without requiring a priori knowledge about the nature of the causative magnetized body. Additionally, inclination and declination angles of both magnetization and ambient field have no effects on the results. In the ELWN technique source geometry, viz., structural index (contact/fault, dyke, horizontal cylinder and sphere) is determined using the depth and exact origin computed previously. Hypothetic simulations performed using TMAs due to some simple shaped geological models have showed the ability of the technique. Moreover, an actual magnetic data taken over the Kesikköprü iron deposit (Central Turkey), one of the largest iron reserve in Turkey,has been also analysed. A depth of 21.39 m has been computed for the magnetized geological source which includes the mafic rocks rich in magnetic properties, and the iron ore body. The structural indices obtained have indicated a dike-like or an intermediate form between a dike and a horizontal cylinder body for the magnetized source. These findings are compatible with those of a recently published study. Hence, the use of ELWN technique is proposed for rapid and reliable model parameter estimations from TMAs as an alternative or supportive experiment to the inverse modelling studies.