scholarly journals An improved space domain algorithm for determining the 3-D structure of the magnetic basement

2019 ◽  
Vol 41 (1) ◽  
pp. 69-80
Author(s):  
Nguyen Thi Thu Hang ◽  
Erdinc Oksum ◽  
Le Huy Minh ◽  
Do Duc Thanh
Keyword(s):  
Magnetic Anomaly ◽  
Science And Technology ◽  
Three Dimensional ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Marine Science ◽  
Euler Deconvolution ◽  
The Earth ◽  
Magnetic Basement ◽  
Basement Structures

The paper presents an improved algorithm based on Bhaskara Rao and Ramesh Babu’s algorithm to invert magnetic anomalies of three-dimensional basement structures. The magnetic basement is approximated by an ensemble of juxtaposed vertical prisms whose bottom surface coincides with Curie surface with the known depth. The computer program operating with the proposed algorithm is built in Matlab environment. Test applications show that the proposed method can perform computations with fast and stable convergence rate where the results also coincide well with the actual model structure. The effectiveness of the method is demonstrated by inverting magnetic anomalies of the southeast part of Vietnam continental shelf. The calculated magnetic basement relief of the study area provides useful additional information for studies in the aim of dealing with the geological structure of the area.References Beiki M., 2010. Analytic signals of gravity gradient tensor and their application to estimate source location, Geophysics, 75(6), i59–i74.Bui C.Q. (chief author), Le T., Tran T. D., Nguyen T. H., Phi T.T., 2007. Map of deep structure of the Earth’s crust, Atlas of the characteristics of natural conditions and environment in Vietnam’s waters and adjacent region. Publisher of Science and Technology, Ha Noi. Do D.T., Nguyen T.T.H., 2011. Atempt the improvement of inversion of magnetic anomalies of two dimensional polygonal cross sections to determine the depth of magnetic basement in some data profile of middle off shelf of Vietnam. Journal of Science and Technology, Vietnam Academy of Science and Technology, 49(2), 125–132.Do D.T., 2013. Study for application of 3D magnetic and gravity method to determine density contribution of basement rock and depth of magnetic basement on Vietnam’s shelf for oil research and prospecting Vietnam National University, Hanoi, Project code QG-11-04. Keating P. and Pilkington M., 2000, Euler deconvolution of the analytic signal, 62nd Annual International Meeting, EAGE, Session P0193.Keating P., Zerbo L., 1996. An improved technique for reduction to the pole at low latitudes, Geophysics, 61, 131–137.Le H.M., Luu V.H., 2003. Preliminary interpretation of the magnetic anomalies of the Eastern Vietnam sea and adiacent regions. J.  Sci. of the Earth, 25(2), 173–181. Mai T.T., Pham V.T., Dang V.B., Le D.B., Nguyen B., Le V.D., 2011. Characteristics of Pliocene - Quaternary geology and Geoengineering in the Center and Southeast parts of Continental Shelf of Vietnam. J.  Sci.  of the Earth, 33(2), 109-118.Mushayandebvu M.F., Lesur V., Reid A.B., Fairhead J.D., 2004. Grid Euler deconvolution with constraints for 2D structures, Geophysics, 69, 489–496.Nguyen N.T., Bui V.N., Nguyen T.T.H., Than D.L., 2014a. Application of power density spectrum of magnetic anomaly to estimate the structure of magnetic layer of the earth crust in the Bac Bo gulf. Journal of Marine Science and Technology, 14(4A), 137–148.Nguyen N.T., Bui V.N., Nguyen T.T.H., 2014b. Determining the depth to the magnetic basementand fault systems in Tu Chinh - Vung May area  by magnetic data interpretation. Journal of Marine Science and Technology, 14(4A), 16–25.Nguyen T.T.H., Pham T.L., Do D.T., Le H.M., 2018. Improving algorithm of determining the coordinates of the vertices of the polygon to invert magnetic anomalies of two-dimensional basement structures in space domain, Journal of Marine Science and Technology (preparing to print).Parker R.L., 1973. The rapid calculation of potential anomalies, Geophys. J. Roy. Astron. Soc, 31, 447–455. Pilkington M., Gregotski M.E., Todoeschuck J.P., 1994. Using fractal crustal magnetization models in magnetic interpretation, Geophysical Prospecting, 42, 677–692.Pilkington M., 2006. Joint inversion of gravity and magnetic data for two-layer models, Geophysics, 71, L35–L42.Rao D.B., Babu N.R., 1993. A fortran 77 computer program for three dimensional inversion of magnetic anomalies resulting from multiple prismatic bodies, Computer & Geosciences, 19(8), 781–801.Tanaka A., Okubo Y., Matsubayashi O., 1999. Curie point depth based on spectrum analysis of the magnetic anomaly data in East and Southeast Asia, Tectonic Pphysics, 306, 461–470.Thompson D.T., 1982. EULDTH – A new technique for marking computer-assisted depth estimates from magnetic data, Geophysics, 47, 31–37.Vo T.S., Le H.M., Luu V.H., 2005. Determining the horizontal position and depth of the density discontinuties in Red River Delta by using the vertical derivative and Euler deconvolution for the gravity anomaly data, Vietnam. Journal of Geology, Series A, 287(3–4), 39–52.  Werner S., 1955. Interpretation of magnetic anomalies of sheet-like bodies, Sveriges Geologiska Undersokning, Series C, Arsbok, 43, 6.Xu S.Z., 2006. The integral-iteration method for continuation of potential fields, Chinese journal of geophysics (in Chinese), 49(4), 1176–1182.Zhang C., Huang D.N., Zhang K., Pu Y.T., Yu P., 2016. Magnetic interface forward and inversion method based on Padé approximation, Applied Geophysics, 13(4), 712–720.CCOP, 1996. Magnetic anomaly map of East Asia, scale 1:4.000.000, Geological survey of Japan and Committee for co-ordination of joint prospecting for mineral resources in asian offshore areas.

Comparison of grid Euler deconvolution with and without 2D constraints using a realistic 3D magnetic basement model

Geophysics ◽  
2005 ◽  
Vol 70 (3) ◽  
pp. L13-L21 ◽  
Author(s):  
Simon E. Williams ◽  
J. Derek Fairhead ◽  
Guy Flanagan
Keyword(s):  
Three Dimensional ◽  
Euler Method ◽  
Magnetic Data ◽  
Data Sets ◽  
Euler Deconvolution ◽  
Data Set ◽  
Distinct Source ◽  
Magnetic Basement ◽  
Modeling Strategy ◽  
Source Geometry

We describe the application of a 2D-constrained grid Euler deconvolution method which is able to determine for each solution window whether the source structure is two dimensional, three dimensional, or poorly defined and to estimate the source location and depth. In each solution window, eigenvalues and eigenvectors are derived from the Euler equations and compared to threshold levels. A single eigenvalue below the given threshold and lying in the x–y-plane is shown to indicate a 2D source, while the absence of such an eigenvalue indicates a 3D source geometry. Two small eigenvalues indicate the field in the window has no distinct source. Applying these criteria to each solution window allows us to generate a map of source-geometry distribution. We evaluate the effectiveness of 2D-constrained grid Euler deconvolution using synthetic magnetic data generated from a 3D basement model based on real topography from an area with surface-exposed faulting. This modeling strategy provides a complex, nonidealized data set that compares Euler depth estimates directly to the known basement surface depth. Our results indicate that noninteger structural indices can be the most appropriate choice for some data sets, and the 2D-constrained grid Euler method images magnetic basement structure more clearly and unambiguously than the conventional grid Euler method.

Gravity and magnetic anomalies of the Sutton Mountains region, Quebec and Vermont: expressions of rift volcanics related to the opening of Iapetus

1981 ◽  
Vol 18 (4) ◽  
pp. 680-692 ◽  
Author(s):  
P. S. Kumarapeli ◽  
A. K. Goodacre ◽  
M. D. Thomas
Keyword(s):  
Gravity Anomaly ◽  
Magnetic Anomaly ◽  
Triple Junction ◽  
Three Dimensional ◽  
Surface Expression ◽  
Magnetic Anomalies ◽  
Iapetus Ocean ◽  
Metavolcanic Rocks ◽  
Gravity And Magnetic ◽  
Narrow Belt

Prominent, nearly coincident, positive gravity and magnetic anomalies occur in the Sutton Mountains region, centered about 100 km east of Montreal, Quebec. Several lines of evidence indicate that the gravity anomaly stems from two principal sources: a deep (mid and lower crustal) source of speculative origin and a shallow source identifiable with a narrow belt of late Precambrian – early Cambrian metavolcanic rocks, the Tibbit Hill volcanics. The magnetic anomaly seems to be produced mainly by the metavolcanic rocks. Three-dimensional modelling of a residual gravity anomaly, supplemented by two-dimensional modelling of the magnetic anomaly, shows that the seemingly minor belt of metavolcanic rocks constitutes the surface expression of a thick (maximum thickness ~8 km) pile of dominantly mafic volcanics, which are only slightly exposed at the present level of erosion.The Tibbit Hill volcanics are regarded as products of rift-related volcanism that occurred at an rrr triple junction developed during the early stages of the opening of the Iapetus Ocean. The Ottawa graben is probably the failed arm of this triple junction. The emplacement of the Grenville dike swarm whose trend is nearly coincident with that of the Ottawa graben was probably coeval with the volcanism in the Sutton Mountains region. The present work shows that the volcanism in the region was on a much larger scale than hitherto recognized.

scholarly journals Pemodelan 2D Batuan Bawah Permukaan Daerah Mamuju Sulawesi Barat Dengan Menggunakan Metode Magnetik

2018 ◽  
Vol 1 (1) ◽  
Author(s):  
Muhammad Irsyad ◽  
Sutrisno Sutrisno ◽  
Dwi Haryanto
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Magnetic Method ◽  
Government Agencies ◽  
Quantitative Interpretation ◽  
Magnetic Intensity ◽  
Contour Map ◽  
A Value ◽  
Qualitative Interpretation ◽  
The Earth

Abstrak. Batuan merupakan benda yang berasal dari magma yang mendingin di dalam bumi. Untuk mengetahui kondisi batuan perlu di lakukan penelitian. Mamuju merupakan daerah yang sedang hangat dalam perbincangan peneliti tentang bagaimana kandungan di bawah permukaan daerah Mamuju, Sulawesi Barat. Daerah ini juga merupakan daerah yang diteliti oleh instansi-instansi pemerintah termasuk PTBGN-BATAN. Penelitian ini bertujuan untuk melakukan pemodelan bawah permukaan bumi. Tujuannya untuk memberikan informasi tentang kondisi baik itu bentuk maupun kedalaman batuan. penelitian ini menggunakan metode magnetik dan metode ini merupakan metode yang tepat untuk membuat model bawah permukaan bumi. Hasil interpretasi kualitatif diperoleh peta kontur intensitas magnetik total dan anomali magnetik. Peta kontur intensitas magnetik total memiliki nilai sebesar 41286,5 – 42280 nT. Sedangkan anomali magnetik memiliki nilai -760,1 – 231,8 nT. Daerah A dan daerah B merupakan daerah yang memiliki anomali tinggi. Hasil interpretasi kuantitatif didapat ada 4 model bawah permukaan yang masing-masing terdapat batuan yang sama yaitu batuan breksi dengan nilai suseptibilitas 0,0006 – 0,00075 satuan cgs dan batuan lava dengan nilai suseptibilitas 0.001 – 0.0015 satuan cgs. daerah yang dilakukan pemodelan fokus pada daerah Hulu Mamuju, hal ini disebabkan karena menurut peta kontur daerah tersebut merupakan daerah yang memiliki anomali magnetik yang tinggi.   Abstract. The rocks are objects derived from the magma cooled in the earth. To determine the condition of the rock is necessary to do research. Mamuju is an area that is warm in conversation investigators about how the content of subsurface area Mamuju, West Sulawesi. This area is also the area investigated by government agencies including PTBGN-BATAN. This study aimed to modeling subsurface. The goal is to provide information about the condition of both the shape and depth of rock. This study uses a magnetic method and this method is an appropriate method to create a model of the earth's subsurface. Qualitative interpretation of results obtained contour map of total magnetic intensity and magnetic anomalies. The total magnetic intensity contour map has a value of 41286.5 to 42280 nT. While the magnetic anomaly has a value of -760.1 - 231.8 nT. Area A and area B is an area that has a high anomaly. Results obtained quantitative interpretation there are 4 models of the subsurface that each contained the same rock is rock breccia with values susceptibility of 0.0006 to 0.00075 cgs units and lava rock with susceptibility value 0.001 - 0.0015 cgs unit. modeling area focuses on upstream area Mamuju, this is because according to the contour map of the area is an area that has a high magnetic anomaly.

scholarly journals IMPROVING ALGORITHM OF DETERMINING THE COORDINATES OF THE VERTICES OF THE POLYGON TO INVERT MAGNETIC ANOMALIES OF TWO-DIMENSIONAL BASEMENT STRUCTURES IN SPACE DOMAIN

2018 ◽  
Vol 18 (3) ◽  
pp. 312-322
Author(s):  
Nguyen Thi Thu Hang ◽  
Pham Thanh Luan ◽  
Do Duc Thanh ◽  
Le Huy Minh
Keyword(s):  
Convergence Rate ◽  
Continental Shelf ◽  
Magnetic Anomalies ◽  
Model Testing ◽  
Two Dimensional ◽  
Stable Convergence ◽  
Space Domain ◽  
Magnetic Basement ◽  
Basement Structures ◽  
Curie Surface

In this paper, we present an improved algorithm based on Murthy and Rao’s algorithm to invert magnetic anomalies of two-dimensional basement structures. Here, the magnetic basement interface is approximated by a 2N-sided polygon with assumption that the bottom of the basement is the Curie surface. The algorithm is built in Matlab environment. The model testing shows that the proposed method can perform computations with fast and stable convergence rate. The obtained result also coincide well with the actual model depth. The practical applicability of the method is also demonstrated by interpreting three magnetic profiles in the southeast part of the continental shelf of Vietnam.

Multiple-source Euler deconvolution

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 525-535 ◽  
Author(s):  
R. O. Hansen ◽  
Laura Suciu
Keyword(s):  
Structural Model ◽  
Complex Structure ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Multiple Source ◽  
Magnetic Data ◽  
Mining District ◽  
Euler Deconvolution ◽  
Source Case ◽  
Location Methods

Rapid three-dimensional (3-D) source location methods can be extremely useful in framing a subsurface structural model from gravity or magnetic data. However, existing implementations of Euler deconvolution are limited to a single source in each window. This can be a significant limitation in areas of complex structure. We have generalized the method to the multiple-source case, and implemented the 3-D algorithm. Results from synthetic data and from the Gold Acres mining district in Nevada suggest that the new algorithm can be a useful interpretive tool.

Kimberlites and exploration geophysics

Geophysics ◽  
1979 ◽  
Vol 44 (8) ◽  
pp. 1395-1416 ◽  
Author(s):  
James C. Macnae
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Magnetic Survey ◽  
Emplacement Mechanism ◽  
Geophysical Technique ◽  
Geologic Model ◽  
Main Factors ◽  
Original Size ◽  
Large Survey

This paper discusses geophysical prospecting techniques for kimberlite pipes, a major source of diamonds. A simple geologic model based on descriptions by Hawthorne (1975) and Nixon (1973) is given, and the varied geophysical responses obtained over kimberlite pipes are interpreted in terms of this model. The three main factors controlling these responses are the original size and inhomogeneity of the pipe, the depth of erosion, and the degree of weathering. Kimberlite pipes are roughly elliptical in surface exposure in most cases, with a “carrot shaped” extension at depth. The unweathered portion of the pipe generally contains a few percent magnetite, and this in most cases produces a clearly detectable magnetic anomaly. The presence of deep weathering may alter the magnetite in the top of the pipe to nonmagnetic oxides of iron, thus resulting in an increased depth to the magnetic source. If this depth is large, the magnetic response may not be large enough to detect the kimberlite in the presence of noise and the effect of other structures. In addition, if little erosion has taken place since emplacement, kimberlitic sediments known as epiclastic kimberlite will be present to considerable depths in the pipe, and this may also lead to the absence of a clear magnetic anomaly. In one large survey in South Africa, electromagnetic (EM) techniques have proven to be remarkably effective in detecting the presence of weathered clays or epiclastic kimberlite contained within the pipes. All pipes discovered during this survey had unmistakable EM signatures, while five out of eight had very small magnetic anomalies which would not likely have been selected as potential targets on the basis of magnetic data alone. These examples would indicate that in any area where deep weathering is expected, an EM survey is essential in combination with a magnetic survey if reconnaissance is to be based on airborne geophysical techniques. Due to the emplacement mechanism of kimberlite, considerable inhomogeneity within a pipe may be present, leading to significant variation in the response of any geophysical technique to one pipe, with resultant interpretation difficulties. Although this is not a limitation in the discovery of new pipes, it does make their geophysical delimitation difficult.

Spatial and temporal analysis of electromagnetic survey data

Geophysics ◽  
1986 ◽  
Vol 51 (1) ◽  
pp. 85-89 ◽  
Author(s):  
Nek R. Garg ◽  
George V. Keller
Keyword(s):  
Survey Data ◽  
Three Dimensional ◽  
Temporal Analysis ◽  
Magnetic Data ◽  
Field Methods ◽  
Transient Electromagnetic ◽  
The Earth ◽  
Earth Structures ◽  
Spatial Spectra ◽  
River Plain

Development of a relatively straightforward approach to interpretation of electromagnetic survey data when the earth in the vicinity of the survey has a complex geoelectric structure will be necessary before such methods can assume their full role in geophysical exploration. One‐dimensional interpretation methods have been well developed to extract the resistivity‐depth profile from a transient electromagnetic (TEM) sounding when the earth is assumed to be simply layered. Extension of the same methods to more complicated earth structures is difficult because of the tedious calculations involved when three‐dimensional earth structures are examined. An alternate approach could be use of the information contained in the spatial spectra of a set of sounding measurements. In such an approach, it should be possible to obtain a clearer concept of the geoelectric structure by analytic continuation of the electromagnetic field in space, or by heuristic filtering of the field, as is done in various potential field methods in geophysics. To try this concept, a filtering technique developed for treating magnetic data was applied to a set of TEM data acquired in the Snake River plain of Idaho. The results are reasonable, but insufficient control information is available to prove their significance. The effort has demonstrated that such a filtering approach can be done quickly, but it places demands on how the field data are sampled in the space domain.

scholarly journals A wavenumber-domain iterative approach for 3D imaging of magnetic anomalies and gradients with depth constraints

2019 ◽  
Vol 16 (6) ◽  
pp. 1032-1047
Author(s):  
Yatong Cui ◽  
Lianghui Guo
Keyword(s):  
Large Scale ◽  
3D Imaging ◽  
Three Dimensional ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Iterative Approach ◽  
Quantitative Interpretation ◽  
Wavenumber Domain ◽  
Large Scale Data ◽  
Scale Data

Abstract Three-dimensional magnetic inversion, based on the least-square and regularization algorithm in the space domain, is an important tool for quantitative interpretation of magnetic data. However, the common 3D inversion approaches usually require great numbers of forward and inversion calculations and cause low efficiency for inverting large-scale data. Three-dimensional imaging is an alternate rapid tool for qualitative and quantitative interpretation of magnetic data. In this paper, we present a wavenumber-domain iterative approach for 3D imaging of magnetic anomalies and gradients, which could increase imaging efficiency and is suitable for rapidly imaging large-scale data. The wavenumber-domain formulas for forward modeling and imaging of total magnetic anomaly, three magnetic components, magnetic gradients and magnetic full-tensor gradients are deduced and provided. A depth-scale factor and the constraints of magnetic interface are included into the imaging formulas to enhance depth resolution. An iterative algorithm is adopted for the imaging to reduce the fitting error and improve the imaging accuracy. Tests on synthetic and real data from the Sichuan basin, China, verified the feasibility of the presented approaches.

Intermediate‐scale magnetic anomalies of the Earth

Geophysics ◽  
1985 ◽  
Vol 50 (12) ◽  
pp. 2817-2830 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
D. W. Strangway
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Anomaly ◽  
Correlation Coefficients ◽  
Sedimentary Basins ◽  
Magnetic Anomalies ◽  
The Earth ◽  
Asymmetric Component ◽  
Anomaly Map ◽  
Well Correlation

Four separate magnetic anomaly maps of the earth are derived from magnetometer satellite data acquired at dawn and at dusk using two different altitude ranges. The magnetic anomalies on the two dawn maps (or dusk maps) are well correlated for spherical harmonics of degree less than 51, suggesting that the time varying external magnetic field and leveling noise have negligible effects on these harmonics. Dawn and dusk maps have an appreciable asymmetric component for harmonics of degree n ⩽ 5 and n = 15 and 17, arising from the quasi‐stable external magnetic field. Dawn‐dusk covariant harmonics of degree [Formula: see text] with signal‐to‐noise ratios greater than 1.5 correlate well. Correlation coefficients are higher than 0.75, implying that these harmonics can be repeatably derived. A global scalar magnetic anomaly map is derived based on these harmonics. The map is then converted to a magnetic susceptibility anomaly map by an inversion technique. The susceptibility anomalies delineate the ocean‐continent differences as well as the boundaries of tectonic provinces, modern uplifts, crustal rifts, and sedimentary basins.

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