Automatic conversion of magnetic data to depth, dip, and susceptibility contrast using the SPI (TM) method

Geophysics ◽  
1997 ◽  
Vol 62 (3) ◽  
pp. 807-813 ◽  
Author(s):  
Jeffrey B. Thurston ◽  
Richard S. Smith
Keyword(s):  
Remanent Magnetization ◽  
Source Parameters ◽  
Thin Sheet ◽  
Source Parameter ◽  
Magnetic Data ◽  
Magmatic Arc ◽  
Peace River ◽  
Magnetic Inclination ◽  
Susceptibility Contrast ◽  
Peace River Arch

The Source Parameter Imaging (SPI™) method computes source parameters from gridded magnetic data. The method assumes either a 2-D sloping contact or a 2-D dipping thin‐sheet model and is based on the complex analytic signal. Solution grids show the edge locations, depths, dips, and susceptibility contrasts. The estimate of the depth is independent of the magnetic inclination, declination, dip, strike and any remanent magnetization; however, the dip and the susceptibility estimates do assume that there is no remanent magnetization. Image processing of the source‐parameter grids enhances detail and provides maps that facilitate interpretation by nonspecialists. The SPI method tests successfully on synthetic profile and gridded data. SPI maps derived from aeromagnetic data acquired over the Peace River Arch area of northwestern Canada correlate well with known basement structure and furthermore show that the Ksituan Magmatic Arc can be divided into several susceptibility subdomains.

Imaging depth, structure, and susceptibility from magnetic data: The advanced source-parameter imaging method

Geophysics ◽  
2005 ◽  
Vol 70 (4) ◽  
pp. L31-L38 ◽  
Author(s):  
Richard S. Smith ◽  
Ahmed Salem
Keyword(s):  
Source Parameters ◽  
Thin Sheet ◽  
Signal Amplitude ◽  
Horizontal Cylinder ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Imaging Method ◽  
Structural Index ◽  
Synthetic Test ◽  
Vertical Contact

An important problem in the interpretation of magnetic data is quantifying the source parameters that describe the anomalous structure. We present a new method that uses various combinations of the local wavenumbers for estimating the depth and shape (structural index) of the structure. Because the estimates are derived from third derivatives of the magnetic data, they are noisy. However, there are multiple ways of calculating the depth and index, and these solutions can be averaged to give a stable estimate. Even so, a synthetic test shows that the results are erratic away from the locations where the analytic-signal amplitude is large. Hence, when we generate images of the depth and structural index, we make the results most visible where the analytic-signal amplitude is large and less visible where the signal is small. The advantage of the method is that estimates can be obtained at all locations on a profile and used to generate continuous profiles or images of the source parameters. This can be used to help identify the locations where interference might be corrupting the results. The structural index image can be used to determine the most appropriate type of model for an area. Assuming this model, it is possible to calculate the depth that would be consistent with the model and the data. Knowing both the depth and model, the analytic-signal amplitude can be converted to apparent susceptibility. If a vertical-contact model is assumed, the susceptibility contrast across the contact can be imaged. For the thin-sheet and horizontal-cylinder models, we can image the susceptibility-thickness and susceptibility-area products, respectively.

Magnetic source parameters of two‐dimensional structures using extended Euler deconvolution

Geophysics ◽  
2001 ◽  
Vol 66 (3) ◽  
pp. 814-823 ◽  
Author(s):  
Martin F. Mushayandebvu ◽  
P. van Driel ◽  
Alan B. Reid ◽  
James Derek Fairhead
Keyword(s):  
Homogeneous Function ◽  
A Priori ◽  
Source Parameters ◽  
Thin Sheet ◽  
Source Location ◽  
Euler Deconvolution ◽  
True Source ◽  
Susceptibility Contrast ◽  
Magnetic Profile ◽  
Constrained Solutions

The Euler homogeneity relation expresses how a homogeneous function transforms under scaling. When implemented, it helps to determine source location for particular potential field anomalies. In this paper, we introduce an additional relation that expresses the transformation of homogeneous functions under rotation. The combined implementation of the two equations, called here extended Euler deconvolution for 2-D structures, gives a more complete source parameter estimation that allows the determination of susceptibility contrast and dip in the cases of contact and thin‐sheet sources. This allows for the structural index to be correctly chosen on the basis of a priori knowledge about susceptibility and dip. The pattern of spray solutions emanating from a single source anomaly can be attributed to interfering sources, which have their greatest effect on the flanks of the anomaly. These sprays follow different paths when using either conventional Euler deconvolution or extended Euler deconvolution. The paths of these spray solutions cross and cluster close to the true source location. This intersection of spray paths is used as a discriminant between poor and well‐constrained solutions, allowing poor solutions to be eliminated. Extended Euler deconvolution has been tested successfully on 2-D model and real magnetic profile data over contacts and thin dikes.

ESTIMATION OF SOURCE PARAMETERS IN IBADAN, SOUTH – WESTERN NIGERIA USING DIGITIZED AEROMAGNETIC DATA

2018 ◽  
Vol 14 (2) ◽  
pp. 15-28
Author(s):  
A A ALABI ◽  
O OLOWOFELA
Keyword(s):  
Magnetic Susceptibility ◽  
Source Parameters ◽  
Granite Gneiss ◽  
Geological Structure ◽  
Magnetic Data ◽  
Susceptibility Map ◽  
Rock Types ◽  
Upward Continuation ◽  
Magnetic Basement ◽  
Local Wavenumber

Airborne magnetic data covering geographical latitudes of 7000‟N to 7030‟N and longitudes of 3 30′E to 4 00′E within Ibadan area were obtained from Nigeria Geology Survey Agency. The data were ana-lyzed to map the sub surface structure and the source parameters were deduced from the quantitative and qualitative interpretation of magnetic data. The upward continuation technique was used to de-emphasize short – wavelength anomaly while the depth to magnetic sources in the area was deter-mined using local wavenumber technique, the analytic signal was also employed to obtain the depths of the magnetic basement. Analysis involving the local wavenumber, upward continuation and appar-ent magnetic susceptibility techniques significantly improves the interpretation of magnetic data in terms of delineating the geological structure, source parameter and magnetic susceptibility within Iba-dan area.. These depth ranges from 0.607km to 2.48km. The apparent susceptibility map at the cut-off wavelength of 50 m ranges from -0.00012 to 0.00079 which agree with the susceptibility value of some rock types; granite gneiss, migmatite biotite gneiss, biotite muscovite granite, hornblende granite, quartz and schists. The result of the local wavenumber suggests variation along the profiles in the surface of magnetic basement across the study area.

Constrained 3D inversion of magnetic data with structural orientation and borehole lithology: A case study in the Macheng iron deposit, Hebei, China

Geophysics ◽  
2019 ◽  
Vol 84 (2) ◽  
pp. B121-B133 ◽  
Author(s):  
Shida Sun ◽  
Chao Chen ◽  
Yiming Liu
Keyword(s):  
Remanent Magnetization ◽  
Magnetic Data ◽  
Iron Deposit ◽  
Reference Field ◽  
Total Field ◽  
Equivalent Source ◽  
Structural Orientation ◽  
Amplitude Data ◽  
Ore Bodies

We have developed a case study on the use of constrained inversion of magnetic data for recovering ore bodies quantitatively in the Macheng iron deposit, China. The inversion is constrained by the structural orientation and the borehole lithology in the presence of high magnetic susceptibility and strong remanent magnetization. Either the self-demagnetization effect caused by high susceptibility or strong remanent magnetization would lead to an unknown total magnetization direction. Here, we chose inversion of amplitude data that indicate low sensitivity to the direction of magnetization of the sources when constructing the underground model of effective susceptibility. To reduce the errors that arise when treating the total-field anomaly as the projection of an anomalous field vector in the direction of the geomagnetic reference field, we develop an equivalent source technique to calculate the amplitude data from the total-field anomaly. This equivalent source technique is based on the acquisition of the total-field anomaly, which uses the total-field intensity minus the magnitude of the reference field. We first design a synthetic model from a simplified real case to test the new approach, involving the amplitude data calculation and the constrained amplitude inversion. Then, we apply this approach to the real data. The results indicate that the structural orientation and borehole susceptibility bounds are compatible with each other and are able to improve the quality of the recovered model to obtain the distribution of ore bodies quantitatively and effectively.

scholarly journals PEMODELAN BAWAH PERMUKAAN MANIFESTASI MINERAL DENGAN METODE GEOMAGNETIK DAERAH PACITAN JAWA TIMUR

KURVATEK ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 25-33
Author(s):  
Fatimah Fatimah
Keyword(s):  
Image Data ◽  
Geological Structure ◽  
Magnetic Data ◽  
Magnetic Intensity ◽  
Magmatic Arc ◽  
The North ◽  
Ore Minerals ◽  
Ore Mineralization ◽  
Extensional Structure ◽  
Anomaly Map

Tulakan Subdistrict, Pacitan Regency, East Java Province. This area is part of the Southern Mountain Zone of East Java, which is the Sunda-Banda magmatic arc of Oligo-Miocene age, where there are alterations and indications of valuable ore minerals. Field magnetic data is taken in an area of 1 x 1 km, with the looping method on the grid trajectory within 200 x 100 m. Then, magnetic data correction and data processing were carried out with Oasis Montaj. From the magnetic anomaly map, the value of high magnetic intensity in the southern part is fresh (intrusive) andesit-dasitic rock as host rock which causes alteration, in the middle has a low magnetic intensity value which is in the direction of the relatively NE-SW river direction, whereas in the north with high intensity is fresh andesite lava. From the image data, it can be seen that the straightness pattern of the geological structure which is dominated by the extensional structure with the direction of NE-SW and E-W is the main trap of epithermal veins carrying ore mineralization mainly Cu, Pb in the study area.

scholarly journals Performance of Two Different Flight Configurations for Drone-Borne Magnetic Data

Sensors ◽  
2021 ◽  
Vol 21 (17) ◽  
pp. 5736
Author(s):  
Filippo Accomando ◽  
Andrea Vitale ◽  
Antonello Bonfante ◽  
Maurizio Buonanno ◽  
Giovanni Florio
Keyword(s):  
Electromagnetic Interference ◽  
Source Parameters ◽  
Spectral Characteristics ◽  
Magnetic Data ◽  
Prototype System ◽  
Control Dataset ◽  
Periodic Data ◽  
Ground Magnetic ◽  
The Stability ◽  
Careful Processing

The compensation of magnetic and electromagnetic interference generated by drones is one of the main problems related to drone-borne magnetometry. The simplest solution is to suspend the magnetometer at a certain distance from the drone. However, this choice may compromise the flight stability or introduce periodic data variations generated by the oscillations of the magnetometer. We studied this problem by conducting two drone-borne magnetic surveys using a prototype system based on a cesium-vapor magnetometer with a 1000 Hz sampling frequency. First, the magnetometer was fixed to the drone landing-sled (at 0.5 m from the rotors), and then it was suspended 3 m below the drone. These two configurations illustrate endmembers of the possible solutions, favoring the stability of the system during flight or the minimization of the mobile platform noise. Drone-generated noise was filtered according to a CWT analysis, and both the spectral characteristics and the modelled source parameters resulted analogously to that of a ground magnetic dataset in the same area, which were here taken as a control dataset. This study demonstrates that careful processing can return high quality drone-borne data using both flight configurations. The optimal flight solution can be chosen depending on the survey target and flight conditions.

Source Parameter Sensitivity of Earthquake Simulations assisted by Machine Learning 

2021 ◽  
Author(s):  
Marisol Monterrubio-Velasco ◽  
J. Carlos Carrasco-Jimenez ◽  
Otilio Rojas ◽  
Juan E. Rodriguez ◽  
David Modesto ◽  
...  
Keyword(s):  
Machine Learning ◽  
High Performance ◽  
Moment Tensor ◽  
Source Parameters ◽  
Velocity Model ◽  
Source Parameter ◽  
Earthquake Simulation ◽  
Centroid Moment Tensor ◽  
Ground Shaking ◽  
Earthquake Simulations

<p>After large magnitude earthquakes have been recorded, a crucial task for hazard assessment is to quickly estimate Ground Shaking (GS) intensities at the affected region. Urgent physics-based earthquake simulations using High-Performance Computing (HPC) facilities may allow fast GS intensity analyses but are very sensitive to source parameter values. When using fast estimates of source parameters such as magnitude, location, fault dimensions, and/or Centroid Moment Tensor (CMT), simulations are prone to errors in their computed GS. Although the approaches to estimate earthquake location and magnitude are consolidated, depth location estimates are largely uncertain. Moreover, automatic CMT solutions are not always provided by seismological agencies, or such solutions are available at later times after waveform inversions allow the determination of moment tensor components. The uncertainty on these parameters, especially a few minutes after the earthquake has been registered, strongly affects GS maps resulting from simulations.</p><p>In this work, we present a workflow prototype to produce an uncertainty quantification method as a function of the source parameters. The core of this workflow is based on Machine Learning (ML) techniques. As a study case, we consider a domain of 110x80 km centered in 63.9ºN-20.6ºW in Southern Iceland, where the 17 best-mapped faults have hosted the historical events of the largest magnitude. We generate synthetic GS intensity maps using the AWP-ODC finite-difference code for earthquake simulation and a one-dimensional velocity model, with 40 recording surface stations. By varying a few source parameters (e.g. event magnitude, CMT, and hypocenter location), we finally model tens of thousands of hypothetical earthquakes. Our ML analog will then be able to relate GS intensity maps to source parameters, thus simplifying sensitivity studies.</p><p>Additionally, the results of this workflow prototype will allow us to obtain ML-based intensity maps a few seconds after an earthquake occurs exploiting the predictive power of ML techniques. We will evaluate the accuracy of these maps as standalone complements to GMPEs and simulations.</p>

Tethys Belt in the Anatolia-Caucasus-Black Sea Region: Basins, Magmatic Arcs, Ophiolites, and LIPs

2021 ◽  
Author(s):  
Vahid Teknik ◽  
Irina Artemieva ◽  
Hans Thybo
Keyword(s):  
Sedimentary Cover ◽  
Arabian Plate ◽  
Magnetic Data ◽  
Poor Correlation ◽  
Black Sea Region ◽  
Nw Iran ◽  
Magmatic Arc ◽  
Sedimentary Sequences ◽  
Mafic Intrusions ◽  
Lesser Caucasus

<p>We interpret the paleotectonic evolution and structure in the Tethyan belt by analyzing magnetic data sensitive to the presence of iron-rich minerals in oceanic fragments and mafic intrusions, hidden beneath sedimentary sequences or overprinted by younger tectono-magmatic events. By comparing the depth to magnetic basement (DMB) as a proxy for sedimentary thickness with average crustal magnetic susceptibility (ACMS), we conclude:</p><p> (1) Major ocean and platform basins have DMB >10 km. Trapped ocean relics may be present below Central Anatolian micro-basins with DMB at 6-8 km and high ACSM.  In intra-orogenic basins, we identify magmatic material within the sedimentary cover by significantly smaller DMB than depth to seismic basement.</p><p>(2) Known magmatic arcs (Pontides and Urima-Dokhtar) have high-intensity heterogeneous ACMS. We identify a 450 km-long buried (DMB >6 km) magmatic arc or trapped oceanic crust along the western margin of the Kirşehır massif from a strong ACMS anomaly. Large, partially buried magmatic bodies form the Caucasus LIP at the Transcaucasus and Lesser Caucasus and in NW Iran.</p><p>(3) Terranes of Gondwana affinity in the Arabian plate, S Anatolia and SW Iran have low-intensity homogenous ACMS.</p><p>(4) Local poor correlation between known ophiolites and ACMS anomalies indicate a small volume of presently magnetized material in the Tethyan ophiolites, which we explain by demagnetization during recent magmatism.</p><p>(5) ACMS anomalies are weak at tectonic boundaries and faults. However, the Cyprus subduction zone has a strong magnetic signature which extends ca. 500 km into the Arabian plate.</p>

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