The Upper Mantle Conductivity Analysis Method Using Observatory Records of the Geomagnetic Field

Campbell, Wilbur H.

doi:10.1007/978-3-0348-7373-4_12

Cited by 10 publications

(21 citation statements)

References 14 publications

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“…Because we find clear evidence for lateral heterogeneity of conductivity in the upper mantle between continental regions, we need to determine what part of each region is best represented by the individual profiles. Some of the difficulties in applying the spherical harmonic coefficients from Sq to the depth-conductivity determination have been discussed in an earlier publication (CAMPBELL, 1987a). Although all observatories of a set are contributing to the SHA analysis, the large potential function values, in the region of the Sq current focus, determine the most significant Legendre polynomials.…”

Section: Discussionmentioning

confidence: 99%

“…With these studies the polynomial coefficients representing separately these equivalent ionospheric source currents and induced eddy currents within the Earth provide us with the ability to evaluate a conductivity profile for each of the continental regions that have a latitudinal distribution of geomagnetic observatories. Our conductivity analysis method, tailored from SCHMUCKER'S (1979) technique for application of the regional geomagnetic observatory records of the Sq field variations, has been described in great detail (CAMPBELL, 1987a). Although it is not necessary to repeat here all of the equations and features of that paper , we should point out some of the special characteristics that will be of particular importance to this present study.…”

Section: Introductionmentioning

confidence: 99%

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Upper mantle electrical conductivity for seven subcontinental regions of the earth.

Campbell

Schiffmacher²

1988

J. geomagn. geoelec

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Spherical harmonic analysis coefficients of the external and internal parts of the quiet-day geomagnetic field variations (Sq) separated for the seven continental regions of the observatories have been used to determine conductivity profiles to depths of about 600km by the Schmucker equivalent substitute conductor method. The profiles give evidence of increases in conductivity between about 150 and 350 km depth, then a general increase in conductivity thereafter. For South America we found a high conductivity at shallow depths. The European profile showed a highly conducting layer near 125km. At the greater depths, Europe, Australia and South America had the lowest values of conductivity. North America and east Asia had intermediate values whereas the African and central Asian profiles both showed the conductivities rising rapidly beyond 450km depth. The regional differences indicate that there may be considerable lateral heterogeneity of electrical conductivity in the Earth's upper mantle.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Upper mantle electrical conductivity for seven subcontinental regions of the earth.

Campbell

Schiffmacher²

1988

J. geomagn. geoelec

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“…A subsequent series of publications extended the Schmucker work with conductivity analyses of continental half-sectors (Campbell and Anderssen, 1983;Campbell and Schiffmacher, 1986, 1988a, 1988bCampbell, 1987Campbell, , 1997Aurora et al, 1995). The method used by these authors first determined a yearly Sq change from the selected quiet-day field variation.…”

Section: Introductionmentioning

confidence: 98%

Quiet-day ionospheric currents and their application to upper mantle conductivity in Australia

et al. 2014

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This study concerns the use of selected geomagnetic field records to establish the 1990 quiet-day current system (Sq) for Australia and to use the ionospheric current source of Sq for a determination of the Earth's deep electrical conductivity. The primary data set came from a chain of eight, three-component magnetometer stations that was operated along a north-south line in central Australia. Additional records, necessary for boundary conditions, were added to the data set. A regional spherical harmonic analysis (SHA) allowed the separation of the internal and external field contributions to the Sq variations. Mapping of the equivalent ionospheric current from the external field showed that the Sq contour focus passed near the -30° geomagnetic latitude of central Australia with a 5°l atitude variation between winter and summer and a corresponding change from about 80 to 200 kA in strength. A special transfer function allowed the computation of an equivalent conductivity-depth profile of central Australia from the paired external and internal coefficients of the SHA. A regression line through the conductivity estimates gives a profile that starts at 0.025 S/m for a depth of 130 km, rising gradually to about 0.045 S/m at 250 km, then steepens to 0.11 S/m at 360 km and rises moderately to 0.13 S/m at 470 km near the base of the upper mantle. No data were obtained through the mantle transition zone. Computations gave 0.18 S/m in the region of 800 km depth. Previous conductivity models for the upper mantle beneath central Australia, although less specific in values, are consistent with our profile. At depths greater than 500 km, the regression profile is in agreement with the conductivity distribution beneath the Tasman Sea determined from seafloor magnetotellurics, although both measurements lack high resolution at such depths.

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“…From that time, improved mathematical techniques, data bases and the application of computers have constantly thrown more light into the understanding of the electrical properties of the inaccessible Earth structure (Campbell, 1989). The geomagnetic field variations recorded at the magnetic observatories facilitate determination of not only the changes in the electrical conductivity within the Earth as a function of depth, but also the external source current systems associated with them (Campbell, 1987(Campbell, , 2003.…”

Section: Introductionmentioning

confidence: 99%

Electrical conductivity of mantle in the North Central region of Nigeria

Obiora

Okeke

Yumoto

2015

Journal of African Earth Sciences

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The Upper Mantle Conductivity Analysis Method Using Observatory Records of the Geomagnetic Field

Cited by 10 publications

References 14 publications

Upper mantle electrical conductivity for seven subcontinental regions of the earth.

Upper mantle electrical conductivity for seven subcontinental regions of the earth.

Quiet-day ionospheric currents and their application to upper mantle conductivity in Australia

Electrical conductivity of mantle in the North Central region of Nigeria

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