Interpretation Of Magnetic Data Research Articles

Enhancing the quality of interpretation magnetic data at low latitudes

Magnetic anomalies are antisymmetrical and often skewed to the location of the sources, because both of the magnetization and ambient field are not directed vertically, so it’s difficult to interpret. For reducing the magnetic anomaly to a symmetrical one – this located on the source of the anomaly – people often use the reduction to the pole (RTP) where the magnetization and ambient field are both directed vertically. However, at low latitudes (an absolute inclination less than 16o30’), the amplitude spectrum of the RTP’s operator was amplified at higher frequencies (short wavelengths) can form a narrow pie-shaped; so it produces artifacts elongated along the direction of the magnetic declination. Therefore, many methods of RTP at low latitudes are given to solve this problem, but most of them are not efficiency. In this paper, we performed enhancing the quality of interpretation of magnetic data at low latitudes by some RTP methods for magnetic data at low latitudes and the analytic signal method using gradient operator and Hilbert transform. This method is applied to a model and to a real magnetic anomaly to find out the best method. Then this method was applied to enhance the quality of magnetic data interpretation in the Southern Vietnam. The result showed that the analytic signal method using Hilbert transform allowed enhancing the quality of interpretatio of magnetic data n at low latitudes is the best.

INVESTIGATION OF JABUNG TEMPLE SUBSURFACE AT PROBOLINGGO, INDONESIA USING RESISTIVITY AND GEOMAGNETIC METHODS

Subsurface structural estimation has been investigated with dipole-dipole resistivity configuration and magnetic methods for mapping of Jabung Temple Archaeological Site located in Jabung Village, Paiton Sub-District, Probolinggo Regency, East Java with Resistivity meter OYO MacOhm and Proton Precession Magnetometer. This estimate aims to determine the spread and depth of the rocks below the surface of the Archaeological Site of Jabung Temple as well as a source of information for the discovery of ancient objects still buried in the soil. The acquisition of resistivity data was performed on ten measuring tracks and covered the measurement area of ± 37,900 m2. Six trajectory tracks are located around Menara Sudut Temple and four line are located in the area of Jabung Temple. The acquisition of magnetic data is made around the area of Jabung Temple at 924 points with spacing of 2.5 meters, with the area of 5,200 m2. Based on the interpretation of magnetic anomaly and resistivity data, the magnetic anomaly value, 22.6 nT due to andesite rock used as a temple booster (based on information obtained during the restoration of 1983/1984). The results of this study indicate that geoelectric and magnetic methods are very effective for the prediction of subsurface structures, especially in the archaeology field.

Response of pedogenic magnetite to changing vegetation in soils developed under uniform climate, topography, and parent material

Pedogenesis produces fine-grained magnetic minerals that record important information about the ambient climatic conditions present during soil formation. Yet, differentiating the compounding effects of non-climate soil forming factors is a nontrivial challenge that must be overcome to establish soil magnetism as a trusted paleoenvironmental tool. Here, we isolate the influence of vegetation by investigating magnetic properties of soils developing under uniform climate, topography, and parent material but changing vegetation along the forest-prairie ecotone in NW Minnesota. Greater absolute magnetic enhancement in prairie soils is related to some combination of increased production of pedogenic magnetite in prairie soils, increased deposition of detrital magnetite in prairies from eolian processes, or increased dissolution of fine-grained magnetite in forest soils due to increased soil moisture and lower pH. Yet, grain-size specific magnetic properties associated with pedogenesis, for example relative frequency dependence of susceptibility and the ratio of anhysteretic to isothermal remanent magnetization, are insensitive to changing vegetation. Further, quantitative unmixing methods support a fraction of fine-grained pedogenic magnetite that is highly consistent. Together, our findings support climate as a primary control on magnetite production in soils, while demonstrating how careful decomposition of bulk magnetic properties is necessary for proper interpretation of environmental magnetic data.

Interpretation of high resolution airborne magnetic data (HRAMD) of Ilesha and its environs, Southwest Nigeria, using Euler deconvolution method

Abstract Interpretation of high resolution aeromagnetic data of Ilesha and its environs within the basement complex of the geological setting of Southwestern Nigeria was carried out in the study. The study area is delimited by geographic latitudes 7°30′–8°00′N and longitudes 4°30′–5°00′E. This investigation was carried out using Euler deconvolution on filtered digitised total magnetic data (Sheet Number 243) to delineate geological structures within the area under consideration. The digitised airborne magnetic data acquired in 2009 were obtained from the archives of the Nigeria Geological Survey Agency (NGSA). The airborne magnetic data were filtered, processed and enhanced; the resultant data were subjected to qualitative and quantitative magnetic interpretation, geometry and depth weighting analyses across the study area using Euler deconvolution filter control file in Oasis Montag software. Total magnetic intensity distribution in the field ranged from –77.7 to 139.7 nT. Total magnetic field intensities reveal high-magnitude magnetic intensity values (high-amplitude anomaly) and magnetic low intensities (low-amplitude magnetic anomaly) in the area under consideration. The study area is characterised with high intensity correlated with lithological variation in the basement. The sharp contrast is enhanced due to the sharp contrast in magnetic intensity between the magnetic susceptibilities of the crystalline and sedimentary rocks. The reduced-to-equator (RTE) map is characterised by high frequencies, short wavelengths, small size, weak intensity, sharp low amplitude and nearly irregular shaped anomalies, which may due to near-surface sources, such as shallow geologic units and cultural features. Euler deconvolution solution indicates a generally undulating basement, with a depth ranging from −500 to 1000 m. The Euler deconvolution results show that the basement relief is generally gentle and flat, lying within the basement terrain.

Joint Interpretation of Geological, Magnetic, AMT, and ERT Data for Mineral Exploration in the Northeast of Inner Mongolia, China

The integrated interpretation of data from various technologies has the potential to obtain a more accurate estimate of subterranean earth properties. In this paper, we implement the joint interpretation of geological and geophysical data for mineral exploration in the northeastern region of Inner Mongolia, China. The joint application of several methodologies reduces the exploration risk. We first determined an approximate and large potential area for mineral exploration with geological data and magnetic data interpretation in Gaoerqi. Results from the two types of data analysis show that the ore deposit strikes roughly east in the northern part of the Gaoerqi mining area. Next, we employed the audio-magnetotelluric (AMT) method to study the subterranean electrical resistivity distribution and divide the earth into four layers. Inverted resistivity sections from the AMT data illustrate that the ore deposits are likely developed in the low-resistivity zone of the survey area from the land surface to 300-m depth. Finally, the high-resolution borehole-to-surface electrical resistivity tomography (ERT) method was employed for further investigation of the location and attitude of the potential ore deposits. Inverted resistivity sections from the ERT data show that two prospective areas for mineral exploration were observed in the west of the survey area and that the eastern portion of the survey area warrants further investigation.

Structural interpretation of aeromagnetic data for the Wadi El Natrun area, northwestern desert, Egypt

The Wadi El Natrun area in Egypt is located west of the Nile Delta on both sides of the Cairo–Alexandria desert road, between 30°00′ and 30°40′N latitude, and 29°40′ and 30°40′E longitude. The name refers to the NW-SE trending depression located in the area and containing lakes that produce natron salt. In spite of the area is promising for oil and gas exploration as well as agricultural projects, Geophysical studies carried out in the area is limited to the regional seismic surveys accomplished by oil companies. This study presents the interpretation of the airborne magnetic data to map the structure architecture and depth to the basement of the study area. This interpretation was facilitated by applying different data enhancement and processing techniques. These techniques included filters (regional-residual separation), derivatives and depth estimation using spectral analysis and Euler deconvolution. The results were refined using 2-D forward modeling along three profiles.Based on the depth estimation techniques, the estimated depth to the basement surface, ranges from 2.25 km to 5.43 km while results of the two-dimensional forward modeling show that the depth of the basement surface ranges from 2.2 km to 4.8 km. The dominant tectonic trends in the study area at deep levels are NW (Suez Trend), NNW, NE, and ENE (Syrian Arc System trend). The older ENE trend, which dominates the northwestern desert is overprinted in the study area by relatively recent NW and NE trends, whereas the tectonic trends at shallow levels are NW, ENE, NNE (Aqaba Trend), and NE. The predominant structure trend for both deep and shallow structures is the NW trend.The results of this study can be used to better understand deep-seated basement structures and to support decisions with regard to the development of agriculture, industrial areas, as well as oil and gas exploration in northern Egypt.

Effects of Magnetic Anisotropy on Total Magnetic Field Anomalies

AbstractModeling of magnetic anomaly data is a powerful technique to gain information on the shape of subsurface rock bodies. Most models are based on the assumption that the magnetization in the source body is parallel to the direction of the Earth's magnetic field. It has long been recognized that remanent magnetization affects the magnetization direction, intensity and shape of the anomaly, and therefore the interpreted structure. The effects of anisotropy, however, have only received little attention so far. This study uses synthetic models and a case study to investigate how anisotropy affects magnetization and anomalies over a thick dipping sheet and determines expected errors in interpreted magnetic properties and geometry of the source body for various anisotropy degrees and field inclinations. Anisotropy affects both the shape and amplitude of anomalies. For an oblate uniaxial fabric with the minimum susceptibility normal to the sheet and P = 1.5, errors in interpreted dip are up to 12°, depending on the field inclination, dip, and profile orientation, and errors in estimated mean susceptibility are up to −30%/+20%, if anisotropy is not taken into account during modeling. These effects are larger for higher degrees of anisotropy. A case study over the megacyclic unit IVe′ layer in the Bjerkreim Sokndal layered intrusion, Norway, investigates the contributions of (an)isotropic induced and remanent magnetizations to the total field anomalies. There, the influence of anisotropy is mainly related to remanence deflection. The results shown here will help to further improve interpretation of magnetic potential field data.

Biological evaluation of the diterpenes from Croton macrostachyus

To clarify whether the seeds of Croton macrostachyus can induce apoptosis, its methanolic extract was first subjected to a clonogenic survival assay, which measures long-term cytotoxic effects. Since it showed cytotoxicity on HCT116 human colon cancer cell lines, further separation was performed, and two single diterpene compounds were obtained. One of them was identified to be a novel compound, methyl 2-(furan-3-yl)-6a,10b-dimethyl-4-oxo-2,4,4a,5,6,6a,10a,10b-octahydro-1H-benzo[f]isochromene-7-carboxylate, based on the interpretation of the nuclear magnetic resonance spectroscopic and mass spectrometric data. Its treatment of HCT116 cells with 50 μg/mL triggered the cleavage of both initiator caspase-9 and effector caspase-7. Moreover, the cleavage of poly (ADP-ribose) polymerase, a substrate of caspase-7, increased after 24 h of treatment. These results demonstrate that this compound exerts antitumor activity by triggering caspase-mediated apoptotic cell death in HCT116 human colon cancer cells.

Modelling of high‐resolution aeromagnetic data to decipher structural deformation in parts of Kaladgi basin, Peninsular India

ABSTRACTWe show the effectiveness of forward and inversion modelling of high‐resolution magnetic data in deciphering the geological framework in a polydeformed Proterozoic Kaladgi basin. The Meso to Neo Proterozoic Kaladgi basin exposes platformal sediments in the northern margin of Dharwar Craton, Peninsular India. The study of high‐resolution magnetic data over Deshnur locality suggests two prominent trends NW–SE and NE–SW, followed by two minor trends of E–W and N–S. Analysis of the magnetic anomalies aided in understanding the succession of deformation events and their impact over sedimentation. The NW–SE trending Nalur shear zone marks the western contact between the Chitradurga Schist belt and Peninsular gneisses that are traced beneath the Badami sediments. The forward model suggests that the NE–SW trending block faulting resulted in generating a series of Horst and Graben structures. Three‐dimensional compact inversion of circular features bearing remanent magnetisation indicates elliptical‐shaped pipe‐like bodies. The three‐dimensional inversion of magnetic data implied thicker sediments within these Graben structures. The basement configuration depicted as elevation of magnetic basement corroborates these three‐dimensional inversion results. The derived results are validated by drill holes, and the intercepts substantiate the inferred structural setup over the study area. Available drill hole and magnetic data interpretation are combined with field information to reconstruct the tectonostratigraphy and the architecture of the Kaladgi basin around Deshnur locality.

Full Tensor Eigenvector Analysis on Air-Borne Magnetic Gradiometer Data for the Detection of Dipole-Like Magnetic Sources.

The detection of dipole-like sources, such as unexploded ordnances (UXO) and other metallic objects, based on a magnetic gradiometer system, has been increasingly applied in recent years. In this paper, a novel dipole-like source detection algorithm, based on eigenvector analysis with magnetic gradient tensor data interpretation is presented. Firstly, the theoretical basis of the eigenvector decomposition of magnetic gradient tensor is analyzed. Then, a detection algorithm is proposed by using the properties of the tensor eigenvector decomposition to locate dipole-like magnetic sources. The algorithm can automatically detect magnetic dipole-like sources without estimating the magnetic moment direction. It performs well for locating weak, anomalous dipole-like sources in air-borne magnetic data through quantitative interpretation. The effectiveness of the proposed algorithm has been demonstrated in the designed synthetic experiment. Finally, an air-borne magnetic field data taken at high altitude with exact source position information is used to validate the practicality of the proposed algorithm. All of the experiments prove that the proposed algorithm is suitable for magnetic dipole-like source detecting and air-borne magnetic gradiometer data interpretation.

New Aromatic Compounds from the Fruiting Body of Sparassis crispa (Wulf.) and Their Inhibitory Activities on Proprotein Convertase Subtilisin/Kexin Type 9 mRNA Expression.

Successive chromatography of EtOAc-soluble extracts of the fruiting body of Sparassis crispa (Wulf.) resulted in isolation of four new aromatic compounds, sparoside A (1) and sparalides A-C (3-5), two new naturally occurring compounds, 2 and 6, and eight known compounds, 7-14. The chemical structures were determined by interpretation of nuclear magnetic resonance and mass spectrometry spectroscopic data. Extract, solvent-soluble fractions of the extract, and all of the pure compounds isolated from the fractions were subjected to the mRNA expression assay for proprotein convertase subtilisin/kexin type 9 (PCSK9). Among them, sparoside A (1), hanabiratakelide A (8), adenosine (11), and 5α,6α-epoxy-(22E,24R)-ergosta-8(14),22-diene-3β,7β-diol (14) exhibited potent inhibitory activities on PCSK9 mRNA expression, with IC50 values of 20.07, 7.18, 18.46, and 8.23 μM, respectively (berberine, positive control, IC50 = 8.04 μM), suggesting that compounds 1, 8, 11, and 14 are suitable for use in supplements to the statins for hyperlipidemia treatments.

Magnetic and Radiometric Signatures over a Proterozoic Massive Sulfide Setting of Northern Fringe of Dalma Volcanics, Eastern India: An implication to Metallogeny

ABSTRACT Magnetic and radiometric surveys were carried out over a felsic dominated rifted margin of Proterozoic volcanic terrain of a mobile belt in the eastern India. The studies were made in blocks I and II of 0.65 sq km and 0.70 sq km respectively over a previously identified conductor in the northern fringe of Dalma Volcanics (DVs). In general, both the blocks show high magnetic signature associated with sulfide mineralisation. The interpretation of magnetic data suggests that nature of the causative source is mainly horizontal cylinder in both the blocks. The depth to the top of the causative source is about 25 m in both the blocks and extends upto 60 m in block I and 40m in block II. Gamma count rate exhibits about a factor of two to three enhancements above the field background for both the blocks. The obtained iso-rad maps are similar to uranium and copper belt in the Singhbhum shear zone south of the study area. The anomalous radiometric signature of the residual soil/rock of the area indicates towards hydrothermal alteration. The detailed magnetic surveys and preliminary iso-rads results seems quite encouraging and may be attributed to VMS setting in the area and potential sulfide mineralisation with uranium mineral association in the DVs province.

Practical considerations in the use of edge detectors for geologic mapping using magnetic data

Locating the edges of magnetized sources provides a fundamental tool in the geologic interpretation of magnetic field data. Much recent effort has been expended on developing improvements to existing edge-detection methods, resulting in purported increases in accuracy and continuity along edges, reduction of noise effects, and limiting the influences of variable depth to source, magnetization direction, and source dip. These endeavors are valuable and provide interpreters with a wider range of tools to carry out geologic interpretations of aeromagnetic data. Nevertheless, survey parameters such as flight height and line spacing impose limits on the quality of edge locations that can be achieved. Using model studies, we quantify the effects that source size, depth, and interference between sources have on calculated edge locations. Based on the known behavior of established edge detectors, we found that many of the newer approaches offer limited advantages over older methods. Consequently, we studied an example of field mapping of geologic contacts in the Canadian Shield, supported by aeromagnetic data, using calculation of a standard edge detector: the horizontal gradient magnitude of the total magnetic field or TF-hgm. Calculated edge locations estimated from this method appear sufficiently accurate and continuous to provide a solid basis on which the mapping campaign was based and executed successfully.

Inversion of borehole magnetic data for prospecting deep‐buried minerals in areas with near‐surface magnetic distortions: a case study from the Daye iron‐ore deposit in Hubei, central China

ABSTRACTSignificant near‐surface magnetic distortions and weakly magnetic responses complicate the interpretation of surface magnetic data and compound difficulties associated with the prospecting of deep‐buried orebodies in old mines, such as the Daye iron‐ore deposit. To address this problem, we used three‐component borehole magnetic measurements from multiple drillholes to evaluate a magnetisation inversion approach that incorporates these data to obtain magnetisation intensity distributions. The magnetisation direction was estimated from rock and ore sample magnetic property measurements. Linear optimisation problem equations were solved using the pre‐conditioned conjugate gradient algorithm. Tests on two‐dimensional synthetic data returned favourable results. In the case study of the Daye iron‐ore deposit, several concealed magnetite orebodies were discovered using three‐component borehole magnetic measurements. Two‐dimensional magnetisation inversion for borehole magnetic data indicated that magnetic sources were located at the contact zones between the diorite and marble rocks, as verified by other drillings. A three‐component borehole magnetic survey shows advantages of moving away from shallow interferences and containing important additional information compared with a surface total field and provides a feasible approach to explore deep‐buried and concealed minerals in areas with strong near‐surface distortions.

Phloroglucinol Derivatives with Protein Tyrosine Phosphatase 1B Inhibitory Activities from Eugenia jambolana Seeds.

Fifteen new phloroglucinol derivatives, jamunones A-O (1-8 and 10-16, respectively), along with one known analogue spiralisone C (9), were isolated from Eugenia jambolana seeds. Their structures were elucidated by detailed nuclear magnetic resonance and mass spectrometry spectroscopic data interpretation. Compounds 1-9, 11, 12, and 14-16 inhibited protein tyrosine phosphatase 1B activity with IC50 values ranging from 0.42 to 3.2 μM.

Correlation imaging method based on local wavenumber for interpreting magnetic data

Depth estimation is a general task in the interpretation of magnetic data, and local wavenumber is an effective tool to accomplish this task, but this method requires the structural index of causative source when applies it to compute the depth of the source, which is hard to obtain for an unknown area. In this paper, we suggested a correlation imaging method to interpret magnetic data, which uses the correlation coefficient of local wavenumber of real magnetic data and transformative local wavenumber of synthetic magnetic data generated by assumed source to estimate the location of the source, and this method does not require any priori information of the source and does not require solving any matrix. The computation steps as follows, first, we assume that the causative sources are distributed regularly as a rectangular grid, and then separately compute the correlation coefficient of the local wavenumber of real data and local wavenumber of the anomaly generated by each assumed source, and the correlation coefficient gets maximum when the location parameters of the assumed source are in accord with the true locations of real sources. The synthetic tested results show that this method can obtain the location of magnetic source effectively and correctly, and is insensitive to magnetization direction and noise. This method is also applied to measured magnetic data, and get the location parameters of the source.

重磁资料解释在地质构造推断上的应用——以渤海湾盆地A区为例

重磁资料解释在地质构造推断上的应用——以渤海湾盆地A区为例

Architecture of the intracontinental Jaibaras Rift, Brazil, based on geophysical data

Qualitative and quantitative integration and interpretation of magnetic, gravity and magnetotelluric data help to determine the internal architecture of the Jaibaras rift, and allow assessing the evolution of the Jaibaras Rift within the Precambrian crystalline basement of Borborema Province, NE Brazil. This was achieved by 2D joint modeling of magnetic and gravity data in five sections across the main axis of the Jaibaras Rift. Surface data, rock density measurements, depth constraints from 2D Euler deconvolution and geophysical information from previous work in the area were integrated to constrain the modeling. The magnetic and gravity profiles of the Jaibaras Rift indicate estimated source bodies at depths up to 2.5 km, showing complex configuration for the structural framework, with a set of asymmetric grabens and horsts. The 2D magnetotelluric inversion shows that the Jaibaras Rift is marked by low resistivity values, and maximum thickness of the sedimentary package up to approximately 3 km. Shallow dipping conductive material may represent either a suture zone between the Ceará Central and Médio Coreaú domains or a set of fractures due to horizontal σ1 stress in the Ceará Central Domain. The Jaibaras Rift displays a very complex internal structure, with discontinuous sequences of grabens and horsts, and a significant volume of surface and subsurface volcanic rocks. The sedimentary packages with volcanic rift sequences have variable thicknesses, from 1 to 3 km. These rock units are controlled by normal faults that developed from older discontinuities, such as the Transbrasiliano lineament.

Application of Petrology & Geology to the Interpretation of Geophysical Data in Defining Economic Porphyry-Related Cu-Au Mineralisation Along the Ekuti Range, Morobe Province, PNG

Detailed petrologic and petrophysic data obtained from surface rock chip and diamond core of the Mt Leahy Tenement, Ekuti Range porphyry copper-gold exploration project area, Morobe Province, Papua New Guinea have been applied to interpretations of geologic setting and hydrothermal environment of mineralisation, and interpretations of airborne magnetic field data in defining a causative intrusion framework for mineralisation. Petrologic data confirm and refine a model of magmatic hydrothermal fluid sources for structurally confined mesothermal to epithermal style Cu, Au, Mo, Ag, Pb, Zn and Bi mineralisation within eroded composite granodiorite, quartz monzodiorite and diorite/andesite intrusion centres and hornfelsed metasedimentary rock, with potential for delineation of “disseminated” porphyry and hornfels styles of mineralisation. The application of petrophysic data, derived from petrology, to the interpretation of airborne magnetic field data defines three intrusion centres within the Leahy tenement: a northern and relatively deeply eroded Otibanda-Weke/Waikanda composite intrusion zone, and higher-level Kopekio and Ekoato intrusion domains, the latter with greater potential for discovery of low-grade high-tonnage style copper-gold mineralisation.

A new approach for the interpretation of magnetic data by a 2-D dipping dike

We have developed a new algorithm for the interpretation of magnetic data measured along a profile by a dipping dike like body. The algorithm is based on the second horizontal gradient (SHG) anomalies calculated from the observed magnetic data using filters of successive window lengths (s). The main merit of this new method is its capability to estimate (successively rather than simultaneously) all the model parameters of the buried anomalous body: depth to top (z), half-width (d), index parameter (α) and amplitude coefficient (K). This technique successively estimates the parameters z, α and K of the anomalous structure at an assumed half-width for various window lengths by solving a nonlinear equation for z and by direct substitution in two consequent formulas in order to infer α and K. The best fitting solution is that for which the root mean square error (RMS) between the observed and predicted data is minimal. The method has been applied to synthetic examples with and without random noise. Following this, it has been applied to three field examples from Canada, China and the United Kingdom which assesses the accuracy of the method. The results were compared against drilling information and published approaches, which highlight the usefulness of the developed approach.