Journal articles: 'Magnetic and gravity data'

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Maus, Stefan. "Variogram analysis of magnetic and gravity data." GEOPHYSICS 64, no. 3 (May 1999): 776–84. http://dx.doi.org/10.1190/1.1444587.

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Model variograms describe the space domain statistics of magnetic and gravity data. Variogram analysis can be used to map intensity, depth, and scaling exponent (self‐correlation) of source. In previous statistical methods the measured data were gridded and transformed to the wavenumber domain; then their power spectrum was analyzed using a spectral model. To avoid the loss and distortion of information during gridding and wavenumber domain transform, I transform the spectral model to the space domain instead. Variograms are the appropriate space domain counterparts of magnetic and gravity power spectra. The variogram of the field above a self‐similar half‐space model is governed by three parameters: intensity, depth, and scaling exponent. These source parameters can be mapped with high resolution and accuracy by fitting model variograms directly to magnetic and gravity line data variograms.

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Hildenbrand, T. G., R. C. Jachens, and R. W. Simpson. "Insights on lithospheric structures within the stable craton U.S.A., based on magnetic and gravity data." Global Tectonics and Metallogeny 6, no. 2 (July 31, 1996): 113–17. http://dx.doi.org/10.1127/gtm/6/1996/113.

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Sutasoma, M., A. Susilo, Sunaryo, E. A. Suryo, S. Minardi, and R. H. D. Cahyo. "Comparison between the magnetic method data of pseudogravity transformation with gravity anomaly data from satellite imagery in the surrounding of the Sutami Dam to identify subsurface formations." Journal of Physics: Conference Series 2165, no. 1 (January 1, 2022): 012017. http://dx.doi.org/10.1088/1742-6596/2165/1/012017.

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Abstract Research has been carried out to determine the subsurface formations in the Sutami dam area and its surroundings using the magnetic method of pseudogravity transformation and satellite imagery gravity anomaly data. This study aims to compare the subsurface formations in the area around the Sutami Dam between the data of the pseodu-gravity transformation magnetic method and the gravity anomaly data of satellite imagery. Data acquisition using the pseudogravity magnetic transformation method was carried out using the Proton Precession Magnetometer (PPM) Scientrex Model G-8 with a spacing of 300 meters. Satellite imagery gravity anomaly data was taken from the Gravity Model Plus (GGM plus) with a spacing of 220 meters. The radius of geomagnetic data acquisition was 15 km. The number of data for the magnetic method of pseudogravity transformation was 1,372 measurement points and satellite imagery gravity anomaly data was 3,000 measurement points. The results showed that the rock formations from the magnetic method of pseudogravity transformation and satellite gravity anomaly data were compatible. There are 4 types of subsurface formations in the study area, namely soil (Δρ = 1.6 g/cm3), Butak Volcanic Product (Δρ = 2 g/cm3), Tuff Deposit (Δρ = 2.1 g/cm3) and Campurdarat Formation (Δρ = 2.6 g/cm3).

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Li, Xiong. "Terracing gravity and magnetic data using edge-preserving smoothing filters." GEOPHYSICS 81, no. 2 (March 1, 2016): G41—G47. http://dx.doi.org/10.1190/geo2015-0409.1.

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One major purpose of gravity and magnetic transformations is to produce a result that can be related to geology. The terracing operator achieves this purpose by converting gravity and magnetic data into a geologic map-like field wherein homogeneous domains with sharp domain boundaries are defined. Edge-preserving smoothing filters developed in image processing have the same capability. I have applied the Kuwahara, mean of least variance, and symmetric nearest neighbor filters to gravity and magnetic data. Synthetic and field data examples suggest that these edge-preserving smoothing filters produce terraced effects cleaner than the terracing operator, and the mean of least variance filter often produces the cleanest and sharpest result.

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Le Magoarou, Camille, Katja Hirsch, Clement Fleury, Remy Martin, Johana Ramirez-Bernal, and Philip Ball. "Integration of gravity, magnetic, and seismic data for subsalt modeling in the Northern Red Sea." Interpretation 9, no. 2 (April 21, 2021): T507—T521. http://dx.doi.org/10.1190/int-2019-0232.1.

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Rifts and rifted passive margins are often associated with thick evaporite layers, which challenge seismic reflection imaging in the subsalt domain. This makes understanding the basin evolution and crustal architecture difficult. An integrative, multidisciplinary workflow has been developed using the exploration well, gravity and magnetics data, together with seismic reflection and refraction data sets to build a comprehensive 3D subsurface model of the Egyptian Red Sea. Using a 2D iterative workflow first, we have constructed cross sections using the available well penetrations and seismic refraction data as preliminary constraints. The 2D forward model uses regional gravity and magnetic data to investigate the regional crustal structure. The final models are refined using enhanced gravity and magnetic data and geologic interpretations. This process reduces uncertainties in basement interpretation and magmatic body identification. Euler depth estimates are used to point out the edges of high-susceptibility bodies. We achieved further refinement by initiating a 3D gravity inversion. The resultant 3D gravity model increases precision in crustal geometries and lateral density variations within the crust and the presalt sediments. Along the Egyptian margin, where data inputs are more robust, basement lows are observed and interpreted as basins. Basement lows correspond with thin crust ([Formula: see text]), indicating that the evolution of these basins is closely related to the thinning or necking process. In fact, the Egyptian Northern Red Sea is typified by dramatic crustal thinning or necking that is occurring over very short distances of approximately 30 km, very proximal to the present-day coastline. The integrated 2D and 3D modeling reveals the presence of high-density magnetic bodies that are located along the margin. The location of the present-day Zabargad transform fault zone is very well delineated in the computed crustal thickness maps, suggesting that it is associated with thin crust and shallow mantle.

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Keating, Pierre. "Density mapping from gravity data using the Walsh transform." GEOPHYSICS 57, no. 4 (April 1992): 637–42. http://dx.doi.org/10.1190/1.1443276.

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One of the main purposes of geophysical mapping is the identification of units that can be related to known geology. On a regional scale, aeromagnetic and gravity maps are the most useful tools presently available, although other techniques such as conductivity mapping (Palacky, 1986) or remote sensing (Watson, 1985) are very helpful in locating lithologic boundaries. Interpretation now makes extensive use of enhanced maps: susceptibility maps for magnetic data, density maps for gravity data, first and second vertical derivative, and horizontal gradient maps for both types of data. The objective of susceptibility and density mapping is to transform the potential field data into a physical property map. For physical property mapping, some hypotheses and simplifications are made. The earth model is assumed to consist of right rectangular prisms of finite (gravity) or infinite (magnetics) depth extent. For ease of data processing, the potential field is interpolated onto a regular rectangular array, so that each point in the array corresponds to one prism.

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RAVI KUMAR, Sistla, and Shaik Kareemunnisa BEGUM. "Interpretation of gravity and magnetic data in the Central Indian Ocean." Contributions to Geophysics and Geodesy 52, no. 3 (September 30, 2022): 359–93. http://dx.doi.org/10.31577/congeo.2022.52.3.2.

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The crustal deformation in the Central Indian Ocean is due to major undulations of the oceanic crust, longitudinal fracture zones, and sea-floor topography. The gravity and magnetic data along with six long profiles across the Central Indian Ocean Basin on W–E tracks between 6°S – 1°S latitudes and 77°E – 90°E longitudes are used to study this deformation. It has been observed that the crustal depths obtained from spectral analysis of gravity and magnetic data are in good agreement with 2D forward gravity modelling results which supports seismic results. The computed seismic velocities for the sediments are 2.0 – 5.7 km/s and 6.1 – 7.7 km/s for the oceanic igneous layer and 8.3 – 8.5 km/s for the oceanic upper mantle are used to determine the densities of oceanic crust with the velocity-density relationship. The average basement depths for all the gravity and magnetic profiles are obtained as ~5 km with deviations of about 1 – 2 km from the mean and for the deeper marker, the crustal depths vary from 9 km to 12 km. In the case of curie isotherm, the crustal depths vary from 9 km to 12 km for all magnetic profiles which may indicate deformation. The crustal top depths vary in the range of 3.5 – 8 km (3.2 – 6 km) and the bottom depth varies in the range of 8.2 – 13.5 km (8.5 – 13 km) for magnetic field anomaly data using the spectral method (the Werner method). The crustal top depths vary in the range of 3.6 – 6.5 km and the bottom depth varies in the range of 7.5 – 11.5 km for free-air anomaly data using the spectral method. The above depths are almost correlated with interpreted 2D gravity modelling and available Seismic results.

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Shamsipour, Pejman, Denis Marcotte, and Michel Chouteau. "3D stochastic joint inversion of gravity and magnetic data." Journal of Applied Geophysics 79 (April 2012): 27–37. http://dx.doi.org/10.1016/j.jappgeo.2011.12.012.

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9

Keating, Pierre B. "Weighted Euler deconvolution of gravity data." GEOPHYSICS 63, no. 5 (September 1998): 1595–603. http://dx.doi.org/10.1190/1.1444456.

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Euler deconvolution is used for rapid interpretation of magnetic and gravity data. It is particularly good at delineating contacts and rapid depth estimation. The quality of the depth estimation depends mostly on the choice of the proper structural index and adequate sampling of the data. The structural index is a function of the geometry of the causative bodies. For gravity surveys, station distribution is in general irregular, and the gravity field is aliased. This results in erroneous depth estimates. By weighting the Euler equations by an error function proportional to station accuracies and the interstation distance, it is possible to reject solutions resulting from aliasing of the field and less accurate measurements. The technique is demonstrated on Bouguer anomaly data from the Charlevoix region in eastern Canada.

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10

Cook, Frederick A., John L. Varsek, and Jeffrey B. Thurston. "Tectonic significance of gravity and magnetic variations along the Lithoprobe Southern Canadian Cordillera Transect." Canadian Journal of Earth Sciences 32, no. 10 (October 1, 1995): 1584–610. http://dx.doi.org/10.1139/e95-128.

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Correlation of potential field data to regional geological features within the Lithoprobe southern Canadian Cordillera transect corridor allows characterization of anomaly patterns according to their likely sources. Long-wavelength Bouguer gravity anomalies are attributed to isostatic effects of topography, which in most areas is compensated. Two notable exceptions occur: in the Foreland belt a large positive isostatic anomaly is likely due to mechanical support of topography formed as Cordilleran thrust sheets were emplaced over the thick craton, and on the west coast, isostatic anomalies are related to active subduction. Long-wavelength magnetic anomalies in the Foreland belt are associated with cratonal basement beneath the thrust sheets, and these can be followed westward to near the Omineca belt. A prominent positive magnetic anomaly along the western Coast belt is probably associated with mafic rocks generated during subduction. Elsewhere, relatively short wavelength gravity and magnetic anomalies correlate well with either plutons (both gravity and magnetic), volcanics (primarily magnetics), or faults (magnetics) within the region of accreted terranes.

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Vatankhah, Saeed, Shuang Liu, Rosemary Anne Renaut, Xiangyun Hu, and Jamaledin Baniamerian. "Improving the use of the randomized singular value decomposition for the inversion of gravity and magnetic data." GEOPHYSICS 85, no. 5 (August 17, 2020): G93—G107. http://dx.doi.org/10.1190/geo2019-0603.1.

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The focusing inversion of gravity and magnetic potential-field data using the randomized singular value decomposition (RSVD) method is considered. This approach facilitates tackling the computational challenge that arises in the solution of the inversion problem that uses the standard and accurate approximation of the integral equation kernel. We have developed a comprehensive comparison of the developed methodology for the inversion of magnetic and gravity data. The results verify that there is an important difference between the application of the methodology for gravity and magnetic inversion problems. Specifically, RSVD is dependent on the generation of a rank [Formula: see text] approximation to the underlying model matrix, and the results demonstrate that [Formula: see text] needs to be larger, for equivalent problem sizes, for the magnetic problem compared to the gravity problem. Without a relatively large [Formula: see text], the dominant singular values of the magnetic model matrix are not well approximated. We determine that this is due to the spectral properties of the matrix. The comparison also shows us how the use of the power iteration embedded within the randomized algorithm improves the quality of the resulting dominant subspace approximation, especially in magnetic inversion, yielding acceptable approximations for smaller choices of [Formula: see text]. Further, we evaluate how the differences in spectral properties of the magnetic and gravity input matrices also affect the values that are automatically estimated for the regularization parameter. The algorithm is applied and verified for the inversion of magnetic data obtained over a portion of the Wuskwatim Lake region in Manitoba, Canada.

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Xu, Kaijun, and Yaoguo Li. "Integrated interpretation of gravity, magnetic, seismic, and well data to image volcanic units for oil-gas exploration in the eastern Junggar Basin, northwest China." Interpretation 8, no. 4 (November 1, 2020): SS113—SS127. http://dx.doi.org/10.1190/int-2019-0280.1.

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We carried out a multigeophysical data joint interpretation to image volcanic units in an area where seismic imaging is difficult due to complicated and variable volcanic lithology. The gravity and magnetic methods can be effective in imaging the volcanic units because volcanic rocks are often strongly magnetic and have large density contrasts. Gravity and magnetic data have good lateral resolution, but they are faced with challenges in defining the depth extent. Although seismic data make for poor imaging in volcanic rocks, they can provide a reliable stratigraphic structure above volcanic rocks to improve the vertical resolution of the gravity and magnetic method. We have developed an integrated interpretation method that combines the advantages of seismic, gravity, magnetic, and well data to generate a 3D quasigeology model to image volcanic units. We first use seismic data to obtain the stratigraphic boundaries, and then we apply an anomaly stripping method based on a seismic-derived structure to extract residual gravity and magnetic anomaly produced by volcanic rocks. We further perform the 3D gravity and magnetic amplitude inversion to recover the distribution of the density and effective susceptibility. We perform geology differentiation using the inverted density and effective magnetic susceptibility to identify the spatial distribution of four groups of volcanic units. The results show that the integrated interpretation of multigeophysical data can significantly decrease the uncertainty associated with any single data set and yield more reliable imaging of lateral and vertical distribution of volcanic rocks.

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13

Raharjo, Wiji, Indiati Retno Palupi, and Oktavia Dewi Alfiani. "New Perspective in Regional and Residual Separation of Gravity and Magnetic Data Processing." RSF Conference Series: Engineering and Technology 1, no. 1 (December 23, 2021): 204–10. http://dx.doi.org/10.31098/cset.v1i1.400.

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Separation between Regional and Residual anomaly in Gravity and Magnetic data processing is very important to get the best result in geological interpretation. Several method were used to solve this problem like upward continuation and polynomial fitting. With the same principle, 2D FFT is applied by make an interactive tools based on Matlab Language Programming, named “Oasis Ala-Ala”. It adopt the algorithm from software Oasis. It started with make visualization map or the original data, then the map divide into some grids. Each of grid contain gravity or magnetic data. Then it transformed from special to wavenumber domain. After that, it convolve with our own filter matrix. And the last step is inverse it to get the regional and residual anomaly map. However, Matlab is powerful in facilitate this process in the GUI Toolbox. One important thing is the size of gravity and magnetic data. It will improve to Filter matrix size before do inverse process.

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Raharjo, Wiji, Indriati Retno Palupi, and Oktavia Dewi Alfiani. "NEW PERSPECTIVE IN REGIONAL AND RESIDUAL SEPARATION OF GRAVITY AND MAGNETIC DATA PROCESSING." Geological Behavior 6, no. 1 (2022): 08–11. http://dx.doi.org/10.26480/gbr.01.2022.08.11.

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Separation between Regional and Residual anomaly in Gravity and Magnetic data processing is very important to get the best result in geological interpretation. Several methods were used to solve this problem like upward continuation and polynomial fitting. With the same principle, 2D FFT is applied by make an interactive tool based on Matlab Language Programming, named “Oasis Ala-Ala”. It adopts the algorithm from software Oasis. It started with make visualization map or the original data, then the map divide into some grids. Each of grid contain gravity or magnetic data. Then it transformed from special to wavenumber domain. After that, it convolves with our own filter matrix. And the last step is inverse it to get the regional and residual anomaly map. However, Matlab is powerful in facilitate this process in the GUI Toolbox. One important thing is the size of gravity and magnetic data. It will improve to Filter matrix size before do inverse process.

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Stampolidis, A., G. Tsokas, A. Kiratzi, and S. Pavlides. "Major tectonic structures in northeastern Greece deduced from geophysical and seismological data." Bulletin of the Geological Society of Greece 40, no. 3 (June 5, 2018): 1279. http://dx.doi.org/10.12681/bgsg.16880.

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We apply lineaments analysis on the gravity and magnetic data of NE Greece, and combine seismological and geophysical data in order to delineate the major structural features. These methods are frequently used for extracting the dimensional and physical parameters of the buried structures that stimulate gravity and magnetic fields. These estimates concern the location, local depth, strike, dip and physical quantity contrast, of potential field contacts. We used results from previous studies in order to correct the Bouguer data for the gravity effect of the crust. The isostatic residual gravity anomalies, produced from the subtraction of the effect of the crust, are related to near-surface features. Noise suppression was achieved by slightly upward continuing the data by one cell size. Geologic significance of detected lineaments is confirmed by comparisons with the known geology, active tectonics and seismicity as well as with topographic lineaments

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Ravi Kumar, Sistla. "Crustal deformation of the Central Indian Ocean, south of Sri Lanka as inferred from gravity and magnetic data." Geology, Geophysics and Environment 48, no. 2 (July 5, 2022): 89–110. http://dx.doi.org/10.7494/geol.2022.48.2.89.

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Bathymetry, gravity, and magnetic data across the Central Indian Ocean Basin (CIOB) along a WE track between 5°N to 1°N latitudes and 77°E to 90°E longitudes are used to identify crustal deformation due to tectonic features such as the Comorin Ridge, 85°E ridge, Ninety East Ridge, and major fracture zones. The tectonic features were interpreted along the North Central Indian Ocean using 2D gravity modelling to understand the origin and tectonic activity of the subsurface features. The Comorin Ridge is coupled with gravity anomalies with small amplitude varying 25–30 mGal in comparison with the ridge relief which suggests that the ridge is compensated at deeper depths. The focus of the present study is to prepare a reasonable crustal model of the Central Indian Ocean using gravity and magnetic data. The crustal depths of the Central Indian Ocean Basin (CIOB) determined from gravity data using the spectral method are compared with the 2D gravity modelling results. It has been observed that the crustal depths obtained from the Spectral method are in good correlation with results obtained from 2D gravity modelling. The average basement depths for the profiles were obtained as ~5 km and perhaps deviated approximately 1–2 km from the mean. In the case of curie isotherm, the crustal depths vary 9–12 km for all magnetic profiles which may indicate deformation.

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Li, Yaoguo, and Douglas W. Oldenburg. "3-D inversion of gravity data." GEOPHYSICS 63, no. 1 (January 1998): 109–19. http://dx.doi.org/10.1190/1.1444302.

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We present two methods for inverting surface gravity data to recover a 3-D distribution of density contrast. In the first method, we transform the gravity data into pseudomagnetic data via Poisson’s relation and carry out the inversion using a 3-D magnetic inversion algorithm. In the second, we invert the gravity data directly to recover a minimum structure model. In both approaches, the earth is modeled by using a large number of rectangular cells of constant density, and the final density distribution is obtained by minimizing a model objective function subject to fitting the observed data. The model objective function has the flexibility to incorporate prior information and thus the constructed model not only fits the data but also agrees with additional geophysical and geological constraints. We apply a depth weighting in the objective function to counteract the natural decay of the kernels so that the inversion yields depth information. Applications of the algorithms to synthetic and field data produce density models representative of true structures. Our results have shown that the inversion of gravity data with a properly designed objective function can yield geologically meaningful information.

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18

Williams, J. P., and V. J. S. Grauch. "Comparison of magnetic and gravity terrain models." Exploration Geophysics 20, no. 2 (1989): 201. http://dx.doi.org/10.1071/eg989201.

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Modelling of magnetic terrain and comparison with actual data is an efficient method for assessing large sets when residual anomalies are important. The technique of Blakely (1981) which utilises a rapidly converging series of Fast Fourier Transforms is an efficient and sufficiently accurate method for this assessment.The technique has been applied to a data set at Kilkivan, south eastern Queensland. Here the magnetic sources are near horizontal Triassic volcanic flows unconformably overlying a non- magnetic Palaeozoic basement.Geological control is good so that it is possible to model the bottom of the flow. It is postulated that the difference between the calculated and actual data represents paleochannels in the basement. Similar techniques applied to gravity data have not been as successful.

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Cascone, Lorenzo, Chris Green, Simon Campbell, Ahmed Salem, and Derek Fairhead. "ACLAS — A method to define geologically significant lineaments from potential-field data." GEOPHYSICS 82, no. 4 (July 1, 2017): G87—G100. http://dx.doi.org/10.1190/geo2016-0337.1.

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Geologic features, such as faults, dikes, and contacts appear as lineaments in gravity and magnetic data. The automated coherent lineament analysis and selection (ACLAS) method is a new approach to automatically compare and combine sets of lineaments or edges derived from two or more existing enhancement techniques applied to the same gravity or magnetic data set. ACLAS can be applied to the results of any edge-detection algorithms and overcomes discrepancies between techniques to generate a coherent set of detected lineaments, which can be more reliably incorporated into geologic interpretation. We have determined that the method increases spatial accuracy, removes artifacts not related to real edges, increases stability, and is quick to implement and execute. The direction of lower density or susceptibility can also be automatically determined, representing, for example, the downthrown side of a fault. We have evaluated ACLAS on magnetic anomalies calculated from a simple slab model and from a synthetic continental margin model with noise added to the result. The approach helps us to identify and discount artifacts of the different techniques, although the success of the combination is limited by the appropriateness of the individual techniques and their inherent assumptions. ACLAS has been applied separately to gravity and magnetic data from the Australian North West Shelf; displaying results from the two data sets together helps in the appreciation of similarities and differences between gravity and magnetic results and indicates the application of the new approach to large-scale structural mapping. Future developments could include refinement of depth estimates for ACLAS lineaments.

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Pettifer, G., A. Tabassi, and B. Simons. "A NEW LOOK AT THE STRUCTURAL TRENDS IN THE ONSHORE OTWAY BASIN, VICTORIA, USING IMAGE PROCESSING OF GEOPHYSICAL DATA." APPEA Journal 31, no. 1 (1991): 213. http://dx.doi.org/10.1071/aj90016.

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Although the Otway Basin is oriented west-north-westerly, and previously recognised major structural elements follow a similar trend, other structural trends have been found on recently obtained geophysical data.In 1989, an aeromagnetic and radiometric survey of the onshore Otway Basin was completed for the Victorian Department of Industry and the Bureau of Mineral Resources, Geology and Geophysics. This survey, together with a recent gravity compilation by the Geological Survey of Victoria, enables analysis of magnetic and gravity data trends reflecting basement and intra-basin structure.The trend analysis was carried out using modern image processing techniques including simulation of real-time sun-angles of the magnetic and gravity data, and composite images of the radiometric data, to highlight lineaments. This technology enables integration of magnetic, gravity, radiometric and, potentially, seismic, Landsat, topography and bathymetry data for basin structure analysis.The magnetic, gravity and radiometric trend analysis was compared to an earlier Landsat study (Baker, 1980) and a previous seismic data compilation of the Otway Basin (Megallaa, 1986).The present study has revealed the significance of major early Palaeozoic north-south and east-north-east to easterly trends. The latter trends have not previously been identified or discussed in earlier basin reviews. There appears to be a difference between trends reflected in the radiometric and seismic data and trends apparent in the gravity and magnetic data. This could indicate a change in principal stress directions during the evolution of the basin. The shape of the northern margin of the basin appears to be controlled by major north-easterly structures.

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Heath, Philip, and Stewart Greenhalgh. "Gravity and magnetic tensor data: Possible use in regolith exploration." ASEG Extended Abstracts 2004, no. 1 (December 2004): 1–4. http://dx.doi.org/10.1071/aseg2004ab067.

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Roy, I. "Pareto optimal 2D joint inversion of gravity and magnetic data." ASEG Extended Abstracts 2009, no. 1 (2009): 1. http://dx.doi.org/10.1071/aseg2009ab046.

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León-Sánchez, Adrián M., Luis A. Gallardo, and A. Yusen Ley-Cooper. "AEM cross-gradient constrained inversion of gravity and magnetic data." ASEG Extended Abstracts 2016, no. 1 (December 2016): 1–6. http://dx.doi.org/10.1071/aseg2016ab178.

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Bosch, Miguel, and John McGaughey. "Joint inversion of gravity and magnetic data under lithologic constraints." Leading Edge 20, no. 8 (August 2001): 877–81. http://dx.doi.org/10.1190/1.1487299.

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Pilkington, M., and P. Keating. "Grid preparation for magnetic and gravity data using fractal fields." Nonlinear Processes in Geophysics 19, no. 2 (April 16, 2012): 291–96. http://dx.doi.org/10.5194/npg-19-291-2012.

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Abstract. Most interpretive methods for potential field (magnetic and gravity) measurements require data in a gridded format. Many are also based on using fast Fourier transforms to improve their computational efficiency. As such, grids need to be full (no undefined values), rectangular and periodic. Since potential field surveys do not usually provide data sets in this form, grids must first be prepared to satisfy these three requirements before any interpretive method can be used. Here, we use a method for grid preparation based on a fractal model for predicting field values where necessary. Using fractal field values ensures that the statistical and spectral character of the measured data is preserved, and that unwanted discontinuities at survey boundaries are minimized. The fractal method compares well with standard extrapolation methods using gridding and maximum entropy filtering. The procedure is demonstrated on a portion of a recently flown aeromagnetic survey over a volcanic terrane in southern British Columbia, Canada.

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Li, Xiong. "Terracing gravity and magnetic data using edge-preserving smoothing filters." GEOPHYSICS 81, no. 2 (February 18, 2016): G37—G43. http://dx.doi.org/10.1190/geo-2015-0409.1.

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Rao, B. Narasimha, P. Ramakrishna, and A. Markandeyulu. "GMINV: A computer program for gravity or magnetic data inversion." Computers & Geosciences 21, no. 2 (March 1995): 301–19. http://dx.doi.org/10.1016/0098-3004(94)00074-5.

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Fedi, Maurizio, and Antonio Rapolla. "3-D inversion of gravity and magnetic data with depth resolution." GEOPHYSICS 64, no. 2 (March 1999): 452–60. http://dx.doi.org/10.1190/1.1444550.

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Magnetization and density models with depth resolution are obtained by solving an inverse problem based on a 3-D set of potential field data. Such a data set is built from information on vertical and horizontal variations of the magnetic or gravity field. The a priori information consists of delimiting a source region and subdividing it in a set of blocks. In this case, the information related to a set of field data along the vertical direction is not generally redundant and is decisive in giving a depth resolution to the gravity and magnetic methods. Because of this depth resolution, which derives solely from the potential field data, an unconstrained and joint inversion of a multiobservation‐level data set is shown to provide surprising results for error‐free synthetic data. On the contrary, a single‐observation level data inversion produces an incorrect and too shallow model. Hence, a good depth resolution is likely to occur for the gravity and magnetic methods when based on the information along the vertical direction. This is also evidenced by an analysis of the kernel function versus the field altitude level and by a singular value analysis of the inversion operators for both the single and multilevel cases. Errors connected to numerical upward continuation do not affect the quality of the solution, provided that the data set extent is larger than that of the anomaly field. Application of the method to a 3-D magnetic data set relative to Vesuvius indicates that the method may significantly improve interpretation of potential fields.

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Saribudak, Mustafa, Michal Ruder, and Bob Van Nieuwenhuise. "Hockley Fault revisited: More geophysical data and new evidence on the fault location, Houston, Texas." GEOPHYSICS 83, no. 3 (May 1, 2018): B133—B142. http://dx.doi.org/10.1190/geo2017-0519.1.

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Ongoing sediment deposition and related deformation in the Gulf of Mexico cause faulting in coastal areas. These faults are aseismic and underlie much of the Gulf Coast area including the city of Houston in Harris County, Texas. Considering that the average movement of these faults is approximately 8 cm per decade in Harris County, there is a great potential for structural damage to highways, utility infrastructure, and buildings that cross these features. Using integrated geophysical data, we have investigated the Hockley Fault, located in the northwest part of Harris County across Highway 290. Our magnetic, gravity, conductivity, and resistivity data displayed a fault anomaly whose location is consistent with the southern portion of the Hockley Fault mapped by previous researchers at precisely the same location. Gravity data indicate a significant fault signature that is coincident with the magnetic and conductivity data, with relatively positive gravity values observed in the downthrown section. Farther north across Highway 290, the resistivity data and the presence of fault scarps indicate that the Hockley Fault appears to be offset to the east, which has not been previously documented. The publicly available LiDAR data and historical aerial photographs of the study area support our geophysical findings. This important geohazard result impacts the mitigation plan for the Hockley Fault because it crosses and deforms Highway 290 in the study area. The nonunique model of the gravity and magnetic data indicates strong correlation of a lateral change in density and magnetic properties across the Hockley Fault. The gravity data differ from the expected signature. The high gravity observed on the downthrown side of the fault is probably caused by the compaction of unconsolidated sediments on the downthrown side. There is a narrow zone of relative negative magnetic anomalies adjacent to the fault on the downthrown side. The source of this magnetization could be due to the alteration of mineralogies by the introduction of fluids into the fault zone.

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Pak, Yong-Chol, Tonglin Li, and Gang-Sop Kim. "2D data-space cross-gradient joint inversion of MT, gravity and magnetic data." Journal of Applied Geophysics 143 (August 2017): 212–22. http://dx.doi.org/10.1016/j.jappgeo.2017.05.013.

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Fregoso, Emilia, and Luis A. Gallardo. "Cross-gradients joint 3D inversion with applications to gravity and magnetic data." GEOPHYSICS 74, no. 4 (July 2009): L31—L42. http://dx.doi.org/10.1190/1.3119263.

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We extend the cross-gradient methodology for joint inversion to three-dimensional environments and introduce a solution procedure based on a statistical formulation and equality constraints for structural similarity resemblance. We apply the proposed solution to the joint 3D inversion of gravity and magnetic data and gauge the advantages of this new formulation on test and field-data experiments. Combining singular-value decomposition (SVD) and other conventional regularizing constraints, we determine 3D distributions of the density and magnetization with enhanced structural similarity. The algorithm reduces some misleading features of the models, which are introduced commonly by conventional separate inversions of gravity and magnetic data, and facilitates an integrated interpretation of the models.

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Benson, Alvin K., and Andrew R. Floyd. "Application of gravity and magnetic methods to assess geological hazards and natural resource potential in the Mosida Hills, Utah County, Utah." GEOPHYSICS 65, no. 5 (September 2000): 1514–26. http://dx.doi.org/10.1190/1.1444840.

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Gravity and magnetic data were collected in the Mosida Hills, Utah County, Utah, at over 1100 stations covering an area of approximately 58 km2 (150 mi2) in order to help define the subsurface geology and assess potential geological hazards for urban planning in an area where the population is rapidly increasing. In addition, potential hydrocarbon traps and mineral ore bodies may be associated with some of the interpreted subsurface structures. Standard processing techniques were applied to the data to remove known variations unrelated to the geology of the area. The residual data were used to generate gravity and magnetic contour maps, isometric projections, profiles, and subsurface models. Ambiguities in the geological models were reduced by (1) incorporating data from previous geophysical surveys, surface mapping, and aeromagnetic data, (2) integrating the gravity and magnetic data from our survey, and (3) correlating the modeled cross sections. Gravity highs and coincident magnetic highs delineate mafic lava flows, gravity lows and magnetic highs reflect tuffs, and gravity highs and magnetic lows spatially correlate with carbonates. These correlations help identify the subsurface geology and lead to new insights about the formation of the associated valleys. At least eight new faults (or fault segments) were identified from the gravity data, whereas the magnetic data indicate the existence of at least three concealed and/or poorly exposed igneous bodies, as well as a large ash‐flow tuff. The presence of low‐angle faults suggests that folding or downwarping, in addition to faulting, played a role in the formation of the valleys in the Mosida Hills area. The interpreted location and nature of concealed faults and volcanic flows in the Mosida Hills area are being used by policy makers to help develop mitigation procedures to protect life and property.

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Hildenbrand, T. G., R. C. Jachens, S. Ludington, and B. Berger. "Relation of regional crustal structures and the distribution of ore deposits in western USA based on magnetic and gravity data." Global Tectonics and Metallogeny 7, no. 2 (December 1, 1999): 105–11. http://dx.doi.org/10.1127/gtm/7/1999/105.

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Chandler, Val W., and Kelley Carlson Malek. "Moving‐window Poisson analysis of gravity and magnetic data from the Penokean orogen, east‐central Minnesota." GEOPHYSICS 56, no. 1 (January 1991): 123–32. http://dx.doi.org/10.1190/1.1442948.

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Analytical correlation of gravity and magnetic data through moving‐window application of Poisson's theorem is useful in studying the complex Precambrian geology of central Minnesota. Linear regression between the two data sets at each window position yields correlation, intercept, and slope parameters that quantitatively describe the relationship between the gravity and magnetic data and, in the case of the slope parameter, are often accurate estimates of magnetizatons‐to‐density ratios (MDR) of anomalous sources. In this study, gridded gravity and magnetic data from a 217.6 × 217.6 km area in central Minnesota were analyzed using a 8.5 × 8.5 km window. The study area includes part of the Early Proterozoic Penokean orogen and an Archean greenstone‐granite terrane of the Superior Province. The parameters derived by the moving‐window analysis show striking relationships to many geologic features, and many of the MDR estimates agree with rock property data. Inversely related gravity and magnetic anomalies are a characteristic trait of the Superior Province, but moving‐window analysis reveals that direct relationships occur locally. In the Penokean fold‐and‐thrust belt, gravity and magnetic highs over the Cuyuna range produce a prominent belt of large MDR estimates, which reflect highly deformed troughs of iron‐formation and other supracrustal rocks. This belt can be traced northeastward to sources that are buried by 3–5 km of Early Proterozoic strata in the Animikie basin. This configuration, in conjunction with recent geologic studies, indicates that the Animikie strata, which may represent foreland basin deposits associated with the Penokean orogen, unconformably overlie parts of the fold‐and‐thrust belt, and that earlier stratigraphic correlations between Cuyuna and Animikie strata are wrong. The results of this study indicate that moving‐window Poisson analysis is useful in the study of Precambrian terranes.

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Blakely, Richard J., and Robert W. Simpson. "Approximating edges of source bodies from magnetic or gravity anomalies." GEOPHYSICS 51, no. 7 (July 1986): 1494–98. http://dx.doi.org/10.1190/1.1442197.

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Cordell and Grauch (1982, 1985) discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks. The final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes. We attempt to automate their final step. Our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources. The method applies to both local surveys and to continent‐wide compilations of magnetic and gravity data (e.g., Zietz, 1982; Simpson et al., 1983a; Kane et al., 1982).

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Cordell, Lindrith, and A. E. McCafferty. "A terracing operator for physical property mapping with potential field data." GEOPHYSICS 54, no. 5 (May 1989): 621–34. http://dx.doi.org/10.1190/1.1442689.

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The terracing operator works iteratively on gravity or magnetic data, using the sense of the measured field’s local curvature, to produce a field comprised of uniform domains separated by abrupt domain boundaries. The result is crudely proportional to a physical‐property function defined in one (profile case) or two (map case) horizontal dimensions. This result can be extended to a physical‐property model if its behavior in the third (vertical) dimension is defined, either arbitrarily or on the basis of the local geologic situation. The terracing algorithm is computationally fast and appropriate to use with very large digital data sets. Where gravity and magnetic data are both available, terracing provides an effective means by which the two data sets can be compared directly. Results of the terracing operation somewhat resemble those of conventional susceptibility (or density) mapping. In contrast with conventional susceptibility mapping, however, the terraced function is a true step function, which cannot be depicted by means of contour lines. Magnetic or gravity fields calculated from the physical‐property model do not, in general, produce an exact fit to the observed data. By intent, the terraced map is more closely analogous to a geologic map in that domains are separated by hard‐edged domain boundaries and minor within‐domain variation is neglected. The terracing operator was applied separately to aeromagnetic and gravity data from a 136 km × 123 km area in eastern Kansas. Results provide a reasonably good physical representation of both the gravity and the aeromagnetic data. Superposition of the results from the two data sets shows many areas of agreement that can be referenced to geologic features within the buried Precambrian crystalline basement. The emerging picture of basement geology is much better resolved than that obtained either from the scanty available drill data or from interpretation of the geophysical data by inspection.

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Fregoso, Emilia, Abel Palafox, and Miguel Angel Moreles. "Initializing Cross-Gradients Joint Inversion of Gravity and Magnetic Data with a Bayesian Surrogate Gravity Model." Pure and Applied Geophysics 177, no. 2 (September 27, 2019): 1029–41. http://dx.doi.org/10.1007/s00024-019-02334-w.

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Ugalde, Hernan, William A. Morris, and Cees van Staal. "The Bathurst Mining Camp, New Brunswick: data integration, geophysical modelling, and implications for exploration." Canadian Journal of Earth Sciences 56, no. 5 (May 2019): 433–51. http://dx.doi.org/10.1139/cjes-2018-0048.

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The Bathurst Mining Camp (BMC) is one of Canada’s oldest mining districts for volcanogenic massive sulphide (VMS) deposits. Most of the 46 known deposits were discovered in the 1950s using a combination of geological and geophysical methods. However, renewed exploration efforts over the past 15 years have not been as successful as one would expect given the level of expenditure of the camp. Nevertheless, this has created a large database of high resolution airborne geophysical data (magnetics, electromagnetics, radiometrics, and full tensor gravity gradiometry) which makes Bathurst a unique case. We show data compilation and map view interpretation, followed by two-and-a-half-dimensional (2.5D) gravity and magnetic modelling. From this, we provide constraints on the folded structure of the mafic and felsic volcanic units, and we interpret a large gravity anomaly in the southeast as a possible ophiolite or a dense thick package of basaltic rocks. Finally, we show an example of 3D modelling in the northwestern part of the camp, where we combine map view interpretation with section-based modelling and 3D geophysical inversion.

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Astromovich, Julia, Mark R. Baker, Diane I. Doser, and William Houston. "Application of gravity and magnetic techniques to model the geometry of the northern margin of the Onion Creek salt diapir, Paradox Basin, Utah." Mountain Geologist 59, no. 1 (February 1, 2022): 5–23. http://dx.doi.org/10.31582/rmag.mg.59.1.5.

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The Onion Creek salt diapir lies within the Paradox Basin of southeast Utah where it forms part of a group of salt structures that separate the Paradox Basin into smaller sub-basins. A series of anomalous, tight folds occur on the northern side of the Onion Creek diapir within the Permian Cutler Group. These folds are thought to be associated with a shallow detachment horizon with three possible origins: 1) a weak shale layer within the Cutler Group; 2) a salt namakier; or 3) a salt shoulder. We collected and analyzed gravity and magnetics data across a portion of the concealed Onion Creek salt body. Since the salt is less dense and less magnetic than the Cutler Group siliciclastics, these geophysical data aid in defining the extent of subsurface salt. Our gravity data show a free-air anomaly low over the diapir with a gradual increase in values as more of the Cutler Group covers the subsurface salt. Magnetic data display a similar trend, but also suggest more complicated 3-D structure exists beneath the study area. Forward and inverse modeling indicated a salt shoulder model best fit the geophysical data. These results suggest gravity and magnetic methods are a low-cost method to evaluate plausible subsurface salt structure for oil and gas exploration studies.

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Broome, H. John. "Generation and interpretation of geophysical images with examples from the Rae Province, northwestern Canada shield." GEOPHYSICS 55, no. 8 (August 1990): 977–97. http://dx.doi.org/10.1190/1.1442927.

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Different types of images generated from gravity, magnetic, and gamma ray spectrometry data from the Rae Province of the Canadian shield were compared with each other and geologic maps to evaluate their effectiveness for displaying the geologically relevant content of the data sets. Shading methods were useful for enhancing weak directional anomalies in the aeromagnetic data. Multi‐directional, shaded‐relief images produced by overlaying three colored, shaded‐relief images are useful for analysis of anomalies associated with structure. Vertical gravity derivative images display a continuous gravity feature linking the Wager Bay and Amer Lake shear zones that is obscured on the Bouguer gravity intensity image. Detailed vertical magnetic derivative images of the shear zone clearly displayed anomalies associated with the internal structure. Composite images generated using three different geophysical parameters show correlations between the magnetic, gravity, and radiometric data which can be related to the geology. Subtle variations in uranium, thorium, and potassium concentrations determined by gamma ray spectrometry can be effectively displayed using ternary radioelement images

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Gerovska, Daniela, Marcos J. Araúzo-Bravo, Petar Stavrev, and Kathryn Whaler. "MaGSoundDST — 3D automatic inversion of magnetic and gravity data based on the differential similarity transform." GEOPHYSICS 75, no. 1 (January 2010): L25—L38. http://dx.doi.org/10.1190/1.3298619.

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We present an automatic procedure — Magnetic And Gravity SOUNDing Differential Similarity Transform (MaGSoundDST) — for inversion of regular or irregular magnetic- and gravity-grid data measured on even or uneven surfaces. It solves for horizontal position, depth, and structural index of simple sources and is independent of a linear background. In addition, it estimates the shape of sources consisting of several singular points and lines. The method uses the property of the differential similarity transform (DST) of a magnetic or a gravity anomaly to become zero or linear at all observation points when the central point of similarity of the transform, which we refer to as the probing point, coincides with a source’s singular point. It uses a measured anomalous field and its calculated or measured (gradiometry) first-order derivatives. The method is independent of the magnetization-vector direction in the magnetic data case and does notrequire reduction-to-the-pole transformed data as input. With MaGSoundDST, we provide an important alternative interpretation technique to the Euler deconvolution procedures, combining a moving-window method, whereby the solutions are linked to singular points of causative bodies, with an approach in which the solutions are linked to the real sources. The procedure involves calculating a 3D function that evaluates the linearity of the DST for different integer or noninteger structural indices, using a moving window. We sound the subsurface along a vertical line under each window center. Then we combine the 3D results for different structural indices and present them in three easy-to-interpret maps, avoiding the need for clustering techniques. We deduce only one solution for location and type of simple sources, which is a major advantage over Euler deconvolution. Application to different cases of synthetic and real data shows the method’s applicability to various types of magnetic and gravity field investigations.

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Alencar de Matos, Caio, and Carlos Alberto Mendonça. "Poisson magnetization-to-density-ratio and magnetization inclination properties of banded iron formations of the Carajás mineral province from processing airborne gravity and magnetic data." GEOPHYSICS 85, no. 5 (July 24, 2020): K1—K11. http://dx.doi.org/10.1190/geo2019-0421.1.

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According to the Poisson theorem, gravity and magnetic fields arising from geologic bodies that share common sources, with a uniform magnetization-to-density ratio (MDR) and a uniform magnetization direction, are related by a linear transformation that allows each field to be calculated from the other. Provided that these conditions on the sources are met, when the gravity and magnetic data are available over an area, the Poisson theorem can be used to infer the MDRs and magnetization directions of sources from their associated gravity and magnetic anomalies. These conditions are partially met in many geologic structures but are expected in iron ore deposits, usually associated with strongly magnetic and highly dense formations. Due to the importance of iron ore as a global commodity, most mineral provinces of the world have been investigated by accurate gravity and magnetic sensors, providing a reliable database, but they have not yet been explored with joint interpretation based on Poisson’s relationships. We have interpreted a gravity-magnetic survey covering the Serra Sul of the Carajás Mineral Province, Brazil, where world-class iron deposits are found. We have adapted a formulation formerly developed to estimate the MDR and the magnetization inclination (MI) from profile data to process gridded data sets. Due to faulting and folding, the same density and magnetic structure may assume different strike directions, requiring corrections to improve MDR and MI estimates. Because the geomagnetic field inclination in the studied area is very low (−6.7°), a procedure for stable computation of the components of the anomalous magnetic field vector is applied. The inferences for Serra Sul MDR suggest minor variations for the entire 30 km long formation containing the mineralized bodies, the strong remanent magnetization showing reverse polarity for banded iron formation segments of the Carajás Serra Sul.

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Prutkin, Ilya, Gerhard Jentzsch, and Thomas Jahr. "Separation of sources and 3D inversion of gravity and magnetic data for the Thuringian Basin, Germany." Contributions to Geophysics and Geodesy 42, no. 2 (January 1, 2012): 119–32. http://dx.doi.org/10.2478/v10126-012-0005-8.

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Separation of sources and 3D inversion of gravity and magnetic data for the Thuringian Basin, Germany We propose a novel methodology for separation of potential field sources and its 3D inversion. New approaches are developed to separate sources: i) in depth using a succession of upward and downward continuation; ii) in the lateral direction by means of approximation with the field of 3D line segments; iii) according to density and magnetization contrast based on pseudo-gravity calculation. Our original inversion algorithms allow the recovery of unknown 3D geometry both for a restricted body of arbitrary shape and for a contact surface. For the first time, we apply our algorithms to joint inversion of gravity and magnetic data for a large area (the Thuringian Basin in central Germany). We separate in depth sources of both gravitational and magnetic anomalies for the whole territory of Thuringia and compare corresponding components. A 3D model of the main sources is presented based on approximation with 3D line segments and their further transforming into a restricted body or a contact surface with the same field.

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Wu, Guochao, Fausto Ferraccioli, Wenna Zhou, Yuan Yuan, Jinyao Gao, and Gang Tian. "Tectonic Implications for the Gamburtsev Subglacial Mountains, East Antarctica, from Airborne Gravity and Magnetic Data." Remote Sensing 15, no. 2 (January 4, 2023): 306. http://dx.doi.org/10.3390/rs15020306.

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The Gamburtsev Subglacial Mountains (GSMs) in interior East Antarctic Craton are entirely buried under the massive ice sheet, with a ~50–60 km thick crust and ~200 km thick lithosphere, but little is known of the crustal structure and uplift mechanism. Here, we use airborne gravity and aeromagnetic anomalies for characteristic analysis and inverse calculations. The gravity and magnetic images show three distinct geophysical domains. Based on the gravity anomalies, a dense lower crustal root is inferred to underlie the GSMs, which may have been formed by underplating during the continental collision of Antarctica and India. The high frequency linear magnetic characteristics parallel to the suture zone suggest that the upper crustal architecture is dominated by thrusts, consisting of a large transpressional fault system with a trailing contractional imbricate fan. A 2D model along the seismic profile is created to investigate the crustal architecture of the GSMs with the aid of depth to magnetic source estimates. Combined with the calculated crustal geometry and physical properties and the geological background of East Antarctica, a new evolutionary model is proposed, suggesting that the GSMs have been a part of the Pan-African advancing accretionary orogen superimposed on the Precambrian basement.

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Heath, Philip J. "The three-dimensional inversion of magnetic and gravity gradient tensor data." ASEG Extended Abstracts 2003, no. 2 (August 2003): 1–4. http://dx.doi.org/10.1071/aseg2003ab069.

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Cassidy, John, Stephen W. Johnston, A. Kirkby, Brodie Klue, and Corinne A. Locke. "The Northland Basin, New Zealand: Analysis of Gravity and Magnetic Data." ASEG Extended Abstracts 2007, no. 1 (December 1, 2007): 1. http://dx.doi.org/10.1071/aseg2007ab180.

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Cevallos, Carlos, Mark Dransfield, Jacqueline Hope, and Heather Carey. "Interpretation of airborne gravity gradiometry and magnetic data using cross-gradients." ASEG Extended Abstracts 2012, no. 1 (December 2012): 1–4. http://dx.doi.org/10.1071/aseg2012ab273.

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Pilkington, Mark. "Joint inversion of gravity and magnetic data for two-layer models." GEOPHYSICS 71, no. 3 (May 2006): L35—L42. http://dx.doi.org/10.1190/1.2194514.

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Gravity and magnetic data are inverted jointly in terms of a model consisting of an interface separating two layers having a constant density and magnetization contrast. A damped least-squares inversion is used to determine the topography of the interface. The inversion requires knowledge of the physical property contrasts across the interface and its average depth. Since the relationship between model parameters and data is weakly nonlinear, a constant damped least-squares inverse is used during the iterative solution search. The effect of this inverse is closely related to a downward continuation of the field to the average interface depth. The method is used to map the base of the Sept-Iles mafic intrusion, Quebec, Canada, and the shape of the central uplift at the Chicxulub impact crater, Yucatan, Mexico. At Sept-Iles, the intrusion reaches a thickness of [Formula: see text], coincident with the maximum gravity anomaly, south of the intrusion center. At Chicxulub, the top of the central uplift is modeled to be [Formula: see text] deep and has a single peak form.

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Henkel, H. "Structural interpretation of gravity and magnetic data in the Nordkalott area." Geologiska Föreningen i Stockholm Förhandlingar 113, no. 2-3 (September 10, 1991): 260–61. http://dx.doi.org/10.1080/11035899109453868.

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Kovacs, L. C., P. Morris, J. Brozena, and A. Tikku. "Seafloor spreading in the Weddell Sea from magnetic and gravity data." Tectonophysics 347, no. 1-3 (March 2002): 43–64. http://dx.doi.org/10.1016/s0040-1951(01)00237-2.

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Journal articles on the topic 'Magnetic and gravity data'

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