Magneto‐gravity response function and its application to the Daito Ridge

Geophysics ◽  
2002 ◽  
Vol 67 (1) ◽  
pp. 110-116 ◽  
Author(s):  
Yoshio Ueda ◽  
Ryuji Kubota ◽  
Jiro Segawa

A magneto‐gravity response function, which shows a phase relationship between magnetic and gravity anomalies caused by a common source body with a constant density‐to‐magnetization ratio, is derived for determining the magnetization direction of a source body for 2‐D and 3‐D cases. The validity of the method is demonstrated through application to test data and to field anomalies from the Daito Ridge. The Daito Ridge is found to be magnetized in the present main field direction, contrary to shallow inclinations suggested by studies of Deep Sea Drilling Project (DSDP) sediment cores. The strong normal magnetization is ascribed to high magnetic susceptibility and/or viscous remanent magnetization.

Geophysics ◽  
1988 ◽  
Vol 53 (3) ◽  
pp. 375-385 ◽  
Author(s):  
R. R. B. von Frese ◽  
D. N. Ravat ◽  
W. J. Hinze ◽  
C. A. McGue

Instabilities and the large matrices which are common to inversions of regional magnetic and gravity anomalies often complicate the use of efficient least‐squares matrix procedures. Inversion stability profoundly affects anomaly analysis, and hence it must be considered in any application. Wildly varying or unstable solutions are the products of errors in the anomaly observations and the integrated effects of observation spacing, source spacing, elevation differences between sources and observations, geographic coordinate attributes, geomagnetic field attitudes, and other factors which influence the conditioning of inversion. Solution instabilities caused by ill‐posed parameters can be efficiently minimized by ridge regression with a damping factor large enough to stabilize the inversion, but small enough to produce an analytically useful solution. An effective choice for the damping factor is facilitated by plotting damping factors against residuals between observed and modeled anomalies and by then comparing this curve to curves of damping factors plotted against solution variance or the residuals between predicted anomaly maps representing the processing objective (e.g., downward continuation, differential reduction to the radial pole, etc.). To obtain accurate and efficient large‐scale inversions of anomaly data, a procedure based on the superposition principle of potential fields may be used. This method involves successive inversions of residuals between the observations and various stable model fields which can be readily accommodated by available computer memory. Integration of the model fields yields a well‐resolved representation of the observed anomalies corresponding to an integrated model which normally could not be obtained by direct inversion because the memory requirements would be excessive. MAGSAT magnetic anomaly inversions over India demonstrate the utility of these procedures for improving the geologic analysis of potential field anomalies.


Geophysics ◽  
2005 ◽  
Vol 70 (6) ◽  
pp. X3-X3
Author(s):  
Yoshio Ueda ◽  
Ryuji Kubota ◽  
Jiro Segawa

To “Magneto-gravity response function and its application to the Daito Ridge,” Yoshio Ueda, Ryuji Kubota, and Jiro Segawa, GEOPHYSICS, 67, 110–116.


Geophysics ◽  
1960 ◽  
Vol 25 (3) ◽  
pp. 569-585 ◽  
Author(s):  
Roland G. Henderson

In the interpretation of magnetic and gravity anomalies, downward continuation of fields and calculation of first and second vertical derivatives of fields have been recognized as effective means for bringing into focus the latent diagnostic features of the data. A comprehensive system has been devised for the calculation of any or all of these derived fields on modern electronic digital computing equipment. The integral for analytic continuation above the plane is used with a Lagrange extrapolation polynomial to derive a general determinantal expression from which the field at depth and the various derivatives on the surface and at depth can be obtained. It is shown that the general formula includes as special cases some of the formulas appearing in the literature. The process involves a “once for all depths” summing of grid values on a system of concentric circles about each point followed by application of the appropriate one or more of the 19 sets of coefficients derived for the purpose. Theoretical and observed multilevel data are used to illustrate the processes and to discuss the errors. The coefficients can be used for less extensive computations on a desk calculator.


1986 ◽  
Vol 17 (4) ◽  
pp. 189-200 ◽  
Author(s):  
D. A. Clark ◽  
S. J. Saul ◽  
D. W. Emerson

2003 ◽  
Vol 40 (10) ◽  
pp. 1307-1320 ◽  
Author(s):  
B Nitescu ◽  
A R Cruden ◽  
R C Bailey

The Moho undulations beneath the western part of the Archean Superior Province have been investigated with a three-dimensional gravity inversion algorithm for a single interface of constant density contrast. Inversion of the complete gravity data set produces unreal effects in the solution due to the ambiguity in the possible sources of some crustal gravity anomalies. To avoid these effects a censored gravity data set was used instead. The inversion results are consistent with reflection and refraction seismic data from the region and, therefore, provide a basis for the lateral correlation of the Moho topography between parallel seismic lines. The results indicate the existence of a major linear east–west-trending rise of the Moho below the metasedimentary English River subprovince, which is paralleled by crustal roots below the granite–greenstone Uchi and Wabigoon subprovinces. This correlation between the subprovincial structure at the surface and deep Moho undulations suggests that the topography of the crust–mantle boundary is related to the tectonic evolution of the Western Superior belts. Although certain features of the crust–mantle boundary are likely inherited from the accretionary and collisional stages of the Western Superior craton, gravity-driven processes triggered by subsequent magmatism and crustal softening may have played a role in both the preservation of those features, as well as in the development of new ones.


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