Conductivity of the subcontinental upper mantle: an analysis using quiet-day geomagnetic records of North America.

Campbell, Wilbur H.; Anderssen, R. S.

doi:10.5636/jgg.35.367

Cited by 30 publications

(21 citation statements)

References 19 publications

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“…Campbell and Anderssen, 1983;Campbell and Schiffmacher, 1988) the cutoff values of Gm were tailored to decrease with increasing m in proportion to the decreasing amplitudes of the Sq field harmonics defined by the (24/m)-hr components. When extensive tests were made on the present data set either making the above m adjustments to GM or by simply assigning it a constant value for all m's, no significant difference was seen.…”

Section: Analysis Methodsmentioning

confidence: 99%

“…Schmucker's method has been shown to be equivalent to other conductivity profile transformations (Weidelt et al, 1980;Jones, 1983;Schmucker, 1987). Campbell and Anderssen (1983) and Campbell (1989) to the continental Sq systems. Campbell and Schiffmacher(1988), compared the seven continental region upper mantle conductivities using the International Quiet Year 1965 geomagnetic data set.…”

Section: Introductionmentioning

confidence: 99%

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Upper Mantle Electrical Conductivity in the Himalayan Region.

Arora

Campbell

Schiffmacher³

1995

J. geomagn. geoelec

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The electrical conductivity profile ofthe Earth at depths of about 50 to 500 km was determined using the quiet ionospheric current variations observed at a line of stations near 75° East longitude. We found conductivity values ofabout 0.06 S/m from 50 to approximately 350 km depth with slight relative maxima near 125 and 275 kin, interpersed by relative minima near 210 and 330 km. Thereafter, the conductivity increased sharply toward a value of about 0.18 S/m at 500 km with no indication of leveling off. A comparison with regional seismic wave-velocity models shows good correspondence between high conductivity and low-velocity zones. The conduction by hydrogen-saturated pyroxene is envisaged as a possible mechanism for the high conductivity and its variation in the upper mantle.

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Section: Analysis Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Upper Mantle Electrical Conductivity in the Himalayan Region.

Arora

Campbell

Schiffmacher³

1995

J. geomagn. geoelec

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“…Using the spectral components of geomagnetic Z and H fields, the long period EM induction responses have been calculated to provide the upper mantle electrical conductivity distribution for the European region (Olsen, 1998) and for the Indian and other global regions (Chandrasekhar, 2000 and references therein). Campbell and Anderssen (1983) generalized the Schmucker's (1970) formulation and developed a method to estimate the complex C(ω)-response directly using the spherical harmonic Gauss coefficients for Sq induction studies. In the present study, we have employed Campbell and Anderssen's (1983) method and calculated induction response estimates, for the periods of Sq and its harmonics.…”

Section: Determination Of Equivalent Ionospheric Source Current Systemsmentioning

confidence: 99%

On the role of oceans in the geomagnetic induction by Sq along the 210° magnetic meridian region

2014

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We have utilized solar quiet daily variation (Sq) data recorded at a network of temporary and permanent magnetic observatories, operated along the western Pacific coast, in the 210• Magnetic Meridian (MM) region, spanning both hemispheres. The selected data sets correspond to solar-quiet year 1996. We have determined the ionospheric source current systems for all three Lloyd's seasons prior to calculating the Sq-induction response. As the selected data sets encompass the whole range of the western Pacific, we studied the role of self-induction effect (SIE) of the ocean at 24-hr period of Sq on the induction response, following the theory developed by Rikitake (1960). Our calculations show a considerable influence of the SIE on the induction response at 24-hr period, implying that ignoring the SIE in induction studies in oceanic regions leads to erroneous interpretation of the results. We have observed a large regional bias in the derived induction response estimates along the 210• MM region. As the ocean effect also depends on the regional subsurface structure and its conductivity, we believe that in addition to the SIE, the bias in the estimated response functions could be due to the strong influence of the coupling of the electric currents induced in the ocean and the highly heterogeneous upper mantle that has resulted from the active lithospheric convergence between the Pacific and Philippine Sea plates all along the western Pacific. We interpret the derived induction responses in the light of the tectonic significance of the 210• MM region. We also discuss the well-defined seasonal differences in ionospheric source current systems by comparing them with those reported for the East Asian sector.

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“…We used a variation of this method that allowed a determination for half-sectors of the Earth representing continental regions. An outline of our SHA method is given in CAMPBELL and SCHIFFMACHER (1985) along with a description of the separations W.H.…”

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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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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Conductivity of the subcontinental upper mantle: an analysis using quiet-day geomagnetic records of North America.

Cited by 30 publications

References 19 publications

Upper Mantle Electrical Conductivity in the Himalayan Region.

Upper Mantle Electrical Conductivity in the Himalayan Region.

On the role of oceans in the geomagnetic induction by Sq along the 210° magnetic meridian region

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

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