A computer program for interpreting vertical magnetic anomalies of spheres and horizontal cylinders

1973 ◽  
Vol 110 (1) ◽  
pp. 2056-2065 ◽  
Author(s):  
B. S. R. Rao ◽  
I. V. Radhakrishna Murthy ◽  
C. Visweswara Rao
Keyword(s):  
Computer Program ◽  
Magnetic Anomalies ◽  
Horizontal Cylinders

On: “Nomogram for the direct interpretation of magnetic anomalies due to long horizontal cylinders,” by T. K. S. Prakasa Rao, M. Subrahmanyam, and A. Srikrishna Murty, (GEOPHYSICS, 51, 2156–2159, November 1986.)

Geophysics ◽  
1987 ◽  
Vol 52 (10) ◽  
pp. 1442-1443
Author(s):  
Ronald Green
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Horizontal Cylinder ◽  
Direct Interpretation ◽  
Horizontal Cylinders

In the article by T. K. S. Prakasa Rao, M. Subrahmanyam, and A. Srikrishna Murty, the trivial problem of interpreting the magnetic anomaly over a horizontal cylinder was examined and a set of nomograms to assist with the interpretation was presented. Prakasa Rao et al. begin their discussion with equation (1) from Gay (1965).

Nomogram for the direct interpretation of magnetic anomalies due to long horizontal cylinders

Geophysics ◽  
1986 ◽  
Vol 51 (11) ◽  
pp. 2156-2159 ◽  
Author(s):  
T. K. S. Prakasa Rao ◽  
M. Subrahmanyam ◽  
A. Srikrishna Murthy
Keyword(s):  
Direct Method ◽  
Linear Equations ◽  
Arbitrary Point ◽  
Magnetic Anomalies ◽  
Horizontal Cylinder ◽  
Empirical Method ◽  
Master Curves ◽  
Hilbert Transforms ◽  
Direct Interpretation ◽  
Horizontal Cylinders

One of the widely used geometrical configurations for magnetic interpretation is the long horizontal circular cylinder. Gay (1965) provides a set of master curves for the interpretation of magnetic anomalies of these bodies. Rao et al. (1973) formulates functions of the anomaly at several distances from an arbitrary point, and the linear equations thus formed are solved for coefficients related to the parameters of the causative body. Prakasa Rao and Murthy (1976) propose an empirical method for rapid interpretation. Atchuta Rao and Ram Babu (1980), Mohan et al. (1982), and Sampath Kumar and Prakasa Rao (1984) describe methods based on Hilbert transforms. Radhakrishna Murthy et al. (1980) propose a method based on two components of the anomalous magnetic field. With the exception of the direct method of Prakasa Rao and Murthy (1976), the other methods mentioned involve reduction of field curves and then matching with master curves, solving linear equations, performing Hilbert transformations, and computation of derivatives, respectively. Hence they are not suitable for direct and rapid interpretation. This note contains a simple nomogram for the magnetic effect due to an arbitrarily magnetized horizontal cylinder.

COMPUTATION WITH THE HELP OF A DIGITAL COMPUTER OF MAGNETIC ANOMALIES CAUSED BY BODIES OF ARBITRARY SHAPE

Geophysics ◽  
1965 ◽  
Vol 30 (5) ◽  
pp. 797-817 ◽  
Author(s):  
Manik Talwani
Keyword(s):  
Computer Program ◽  
Gravitational Potential ◽  
Digital Computer ◽  
Arbitrary Shape ◽  
Complex Shape ◽  
Magnetic Anomalies ◽  
Simple Geometry ◽  
Second Derivatives ◽  
First Vertical Derivative ◽  
Derivatives Of

Formulas are derived for the magnetic anomalies caused by irregular polygonal laminas. These are used to obtain the three components of the magnetic anomalies caused by a finite homogeneously magnetized body of arbitrary shape. There is no restriction to the direction of magnetization; in general, it may not be the same as that of the earth’s field. Total‐intensity anomalies are also obtained. Use of these formulas in a computer program is discussed and illustrated by computing the anomaly caused by Caryn Seamount. Simplified, formulas are presented for the anomalies caused by finite rectangular laminas. In addition to bodies of complex shape, the computer program can also be profitably used for computing the magnetic anomalies caused by bodies of relatively simple geometry. The second derivatives of the gravitational potential of a massive body, that is, quantities familiarly known as gradient and curvature in torsion‐balance work and the first vertical derivative in gravity work are also obtained by this method.

Magnetic interpretation using a least-squares, depth-shape curves method

Geophysics ◽  
2005 ◽  
Vol 70 (3) ◽  
pp. L23-L30 ◽  
Author(s):  
El-Sayed M. Abdelrahman ◽  
Khalid S. Essa
Keyword(s):  
Least Squares ◽  
Magnetic Anomaly ◽  
Least Squares Method ◽  
Random Noise ◽  
Synthetic Data ◽  
Theoretical Data ◽  
Magnetic Anomalies ◽  
Shape Factors ◽  
Characteristic Points ◽  
Horizontal Cylinders

We have developed a least-squares approach to depth determination from residual magnetic anomalies caused by simple geologic structures. By normalizing the residual magnetic anomaly using three characteristic points and their corresponding distances on the anomaly profile, the problem of determining depth from residual magnetic anomalies has been transformed into finding a solution to a nonlinear equation of the form z = f(z). Formulas have been derived for spheres, horizontal cylinders, thin dikes, and contacts. The method is applied to synthetic data with and without random noise. We have also developed a method using depth-shape curves to simultaneously define the shape and depth of a buried structure from a residual magnetic anomaly profile. The method is based on determining the depth from the normalized residual anomaly for each shape factor using the least-squares method mentioned above. The computed depths are plotted against the shape factors on a graph. The solution for the shape and depth of the buried structure is read at the common intersection of the depth-shape curves. The depth-shape curves method was successfully tested on theoretical data with and without random noise and applied to a known field example from Ontario.

STANDARD CURVES FOR MAGNETIC ANOMALIES OVER LONG HORIZONTAL CYLINDERS

Geophysics ◽  
1965 ◽  
Vol 30 (5) ◽  
pp. 818-828 ◽  
Author(s):  
S. Parker Gay
Keyword(s):  
Circular Cylinder ◽  
Magnetic Anomalies ◽  
Curve Matching ◽  
Profile Curve ◽  
Complete Family ◽  
Family Of Curves ◽  
Isolated Points ◽  
Horizontal Cylinders ◽  
Magnetizing Field ◽  
Horizontal Circular Cylinder

The magnetic anomalies in Z, H, and [Formula: see text] for the long horizontal circular cylinder are shown to belong to a single mathematical family of curves for all values of strike and all values of inclination of the magnetizing field, a characteristic that was previously shown to hold for long tabular bodies, or dikes (Gay, 1963). The complete family of standard curves has been constructed and is incorporated into an interpretational scheme based on superposition with observed magnetic profiles. Comparison of cylinder anomalies with dike anomalies shows only slight differences in the two types of curves, which would be very difficult, if not impossible, to detect using interpretational methods based on a few isolated points of a profile curve, such as half‐width, distance between maximum and minimum, etc. Curve‐matching, or superposition, appears to be mandatory for reliable quantitative interpretations.

Relationship of magnetic anomalies due to subsurface features and the interpretation of sloping contacts

Geophysics ◽  
1980 ◽  
Vol 45 (1) ◽  
pp. 32-36 ◽  
Author(s):  
D. Atchuta Rao ◽  
H. V. Ram Babu ◽  
P. V. Sanker Narayan
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Horizontal Cylinder ◽  
Horizontal Derivative ◽  
Horizontal Cylinders ◽  
Relationship Of

A study of the magnetic anomalies produced by sloping geologic contacts, thin dikes, and horizontal cylinders has revealed that a single relationship exists among the magnetic anomalies created by them. The magnetic anomaly due to a horizontal cylinder, the first horizontal derivative of the magnetic anomaly due to a thin dike, and the second horizontal derivative of the magnetic anomaly due to a sloping contact are found to be identical in shape. Gay (1963, 1965) presented standard curves to interpret the magnetic anomalies over long tabular bodies (1963) and long horizontal cylinders (1965). It is shown here that the same curves can also be used to interpret the total, vertical and horizontal magnetic anomalies due to sloping geologic contacts.

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