scholarly journals GRAV MAG PRISM: A MATLAB /OCTAVE PROGRAM TO GENERATE GRAVITY AND MAGNETIC ANOMALIES DUE TO RECTANGULAR PRISMATIC BODIES

2013 ◽  
Vol 31 (3) ◽  
pp. 347 ◽  
Author(s):  
Alessandra De Barros e Silva Bongiolo ◽  
Jeferson De Souza ◽  
Francisco José Fonseca Ferreira ◽  
Luís Gustavo De Castro
Keyword(s):  
Potential Field ◽  
Magnetic Anomalies ◽  
Field Modeling ◽  
Gravity And Magnetic ◽  
Ascii Format ◽  
Arbitrary Dimensions ◽  
Prismatic Bodies

ABSTRACT. In this paper we present the GRAV MAG PRISM code to generate synthetic gravity and magnetic anomalies from rectangular prismatic bodies with arbitrary dimensions, densities and magnetizations. The code has been developed in a MATLAB/OCTAVE environment and provides a graphical and a numerical output, as well. The data are written in xyz (ASCII) format and can be contaminated with noise. We also summarize the theory and show some examples of the program’s applications. The code can be used for research and educational purposes and is freely-distributed by the authors on request.Keywords: gravity and magnetic anomalies, potential-field modeling, program. RESUMO. Neste trabalho é apresentado o programa GRAV MAG PRISM, o qual gera anomalias de gravidade e magnéticas sintéticas a partir de corpos prismáticos retangulares com dimensões, densidades e magnetizações arbitrárias. O código foi desenvolvido em ambiente MATLAB/OCTAVE, com saídas gráficas e numéricas. Os dados são escritos no formato xyz (ASCII) e podem ser contaminados por ruídos. Neste trabalho também é apresentado um resumo da teoria e alguns exemplos de aplicação do programa. O código acompanha um tutorial e pode ser utilizado para fins educacionais e de pesquisa, sendo de distribuição gratuita através de solicitação aos autores.Palavras-chave: anomalias gravimétricas e magnéticas, modelagem de campos potenciais, programa.

scholarly journals GRAVITY AND MAGNETIC SIGNATURE OF THE TRANSBRASILIANO LINEAMENT IN THE EAST-CENTRAL PORTION OF THE PARNAÍBA BASIN, NORTHEASTERN BRAZIL

2017 ◽  
Vol 35 (1) ◽  
Author(s):  
Thuany Patrícia Costa de Lima ◽  
Emanuel Ferraz Jardim de Sá ◽  
Fernando Antonio Pessoa Lira Lins ◽  
Alex Francisco Antunes ◽  
José Antônio De Morais Moreira
Keyword(s):  
Shear Zone ◽  
Potential Field ◽  
Field Data ◽  
Magnetic Anomalies ◽  
Northeastern Brazil ◽  
Central Portion ◽  
East Central ◽  
Potential Field Data ◽  
Gravity And Magnetic ◽  
Parnaíba Basin

ABSTRACT. The Transbrasiliano Lineament (TBL) corresponds to a NE-trending mega shear zone of late Neoproterozoic age with an extensive segment underneath the Parnaíba Basin (northeastern Brazil); the Eopaleozoic to Mesozoic section of the basin evidence the lineament’s brittle reactivation events. This paper presents a case study of TBL in the east-central portion of Parnaíba Basin with a special concern to the characterization of pre-Silurian grabens in the basement. The approach involves the interpretation of potential field data and seismic reflection line based on a plastic dextral transcurrent mega shear zone model. The gravity anomaly belts display a curvilinear shape joining the NE trend of the TBL, in accordance to a dextral S-C pair. A retrogressive stage with narrower ductile-brittle dextral structures controlled the opening of pull-apart grabens. Magnetic anomalies seem to be related to these late structures. The integration of the map analyses, seismic interpretation and 2D gravity modeling led to the conclusion that the sources causing the gravity and magnetic anomalies in the basin result from mass variations related to anisotropies of the crystalline basement and crustal heterogeneities, such as granite plutons, metasedimentary belts, shear zones and pre-Silurian grabens. The delimitation of grabens underneath the Parnaíba Basin suffers severe restrictions when solely interpreted based on potential field data. Keywords: gravity forward modeling, Transbrasiliano Lineament, magnetic anomaly. RESUMO. O Lineamento Transbrasiliano (LTB) corresponde a uma megazona de cisalhamento com direção NE, de idade Neoproterozoica, com um extenso segmento subjacente à Bacia do Parnaíba; a seção Eopaleozoica a Mesozoica da bacia evidencia seus eventos de reativação. Este trabalho aborda o LTB na porção centro-leste da Bacia do Parnaíba, com especial atenção à caracterização de grabens pré-Silurianos do embasamento. A abordagem envolve interpretações de dados de métodos potenciais e de linha sísmica de reflexão baseadas em um modelo de megazona de cisalhamento plástica transcorrente dextral. As faixas de anomalias gravimétricas exibem uma geometria curvilínea, aproximando-se em direção ao trend NE do Lineamento Transbrasiliano, em consonância a um par S-C dextral. Um estágio retrogressivo com estruturas dúcteis-frágeis mais estreitas controlaram a abertura de grabens pull-apart. As anomalias magnéticas imageam essas estruturas tardias. A integração da análise de mapas de anomalia, interpretação sísmica e modelagem gravimétrica 2D permite concluir que as fontes causadoras das anomalias gravimétricas e magnéticas na bacia resultam de variações de massa relacionadas a heterogeneidades crustais e às anisotropias do embasamento cristalino, tais como plútons graníticos, faixas de metassedimentos e zonas de cisalhamento, com contribuição subordinada dos grabens pré-Silurianos. A delimitação desses grabens subjacentes à Bacia do Parnaíba sofre severas restrições quando interpretadas unicamente com base nos dados de métodos potenciais. Palavras-chave: modelagem gravimétrica direta, Lineamento Transbrasiliano, anomalia magnética.

SPECTRAL ANALYSIS OF GRAVITY AND MAGNETIC ANOMALIES DUE TO RECTANGULAR PRISMATIC BODIES

Geophysics ◽  
1977 ◽  
Vol 42 (1) ◽  
pp. 41-50 ◽  
Author(s):  
B. K. Bhattacharyya ◽  
Lei‐Kuang Leu
Keyword(s):  
Spectral Analysis ◽  
Approximation Method ◽  
Magnetic Anomalies ◽  
The Body ◽  
Exponential Approximation ◽  
Prismatic Body ◽  
First Order ◽  
Gravity And Magnetic ◽  
Sums Of Exponentials ◽  
Prismatic Bodies

The spectra of gravity and magnetic anomalies due to a prismatic body can be expressed as sums of exponentials. The complex exponents of these exponentials are functions of frequency and locations of the corners of the body. An exponential approximation method is used for the analysis of the radial spectra of an anomaly and its first order moments for obtaining accurate estimates of the depths to the top and bottom of the body. A method has also been developed for determining approximately the location of the centroid of the body. When the location of the centroid and the depths to the top and bottom are known for the causative body, it is possible to calculate the horizontal dimensions with the help of the spectrum of the anomaly.

A DIRECT COMPUTATION OF GRAVITY AND MAGNETIC ANOMALIES CAUSED BY 2- AND 3-DIMENSIONAL BODIES OF ARBITRARY SHAPE AND ARBITRARY MAGNETIC POLARIZATION BY EQUIVALENT‐POINT METHOD AND A SIMPLIFIED CUBIC SPLINE

Geophysics ◽  
1977 ◽  
Vol 42 (3) ◽  
pp. 610-622 ◽  
Author(s):  
Chao C. Ku
Keyword(s):  
Arbitrary Shape ◽  
Gaussian Quadrature ◽  
Magnetic Anomalies ◽  
Cubic Spline ◽  
The Body ◽  
Point Method ◽  
Magnetic Polarization ◽  
3 Dimensional ◽  
Equivalent Point ◽  
Gravity And Magnetic

A computational method, which combines the Gaussian quadrature formula for numerical integration and a cubic spline for interpolation in evaluating the limits of integration, is employed to compute directly the gravity and magnetic anomalies caused by 2-dimensional and 3-dimensional bodies of arbitrary shape and arbitrary magnetic polarization. The mathematics involved in this method is indeed old and well known. Furthermore, the physical concept of the Gaussian quadrature integration leads us back to the old concept of equivalent point masses or equivalent magnetic point dipoles: namely, the gravity or magnetic anomaly due to a body can be evaluated simply by a number of equivalent points which are distributed in the “Gaussian way” within the body. As an illustration, explicit formulas are given for dikes and prisms using 2 × 2 and 2 × 2 × 2 point Gaussian quadrature formulas. The basic limitation in the equivalent‐point method is that the distance between the point of observation and the equivalent points must be larger than the distance between the equivalent points within the body. By using a reasonable number of equivalent points or dividing the body into a number of smaller subbodies, the method might provide a useful alternative for computing in gravity and magnetic methods. The use of a simplified cubic spline enables us to compute the gravity and magnetic anomalies due to bodies of arbitrary shape and arbitrary magnetic polarization with ease and a certain degree of accuracy. This method also appears to be quite attractive for terrain corrections in gravity and possibly in magnetic surveys.

scholarly journals Depositional and Structural Styles in the Logone Birni Basin (LBB), Northern Cameroon, from 3D Potential Field Modeling: Preliminary Results

2019 ◽  
Vol 09 (04) ◽  
pp. 226-244 ◽  
Author(s):  
Elad Mkoumbe ◽  
Fosso Téguia M. Estelle Eric ◽  
Eyike Yomba Albert ◽  
Njandjock Nouck Philippe ◽  
Tabod Charles Tabod
Keyword(s):  
Potential Field ◽  
Preliminary Results ◽  
Field Modeling ◽  
Northern Cameroon
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