Abstract
Electrical conductivity structure of the Earth’s deep interior has been successfully mapped out down to approximately 1500 km around the geomagnetic dip equatorial regions of Africa using solar quiet-day ionospheric currents. Spherical harmonic analysis (SHA) was employed in separating the internal and external field contributions to the solar quiet variations. Transfer function was used for each of the external and internal pairs to compute the conductivity-depth profile for the region. Calculated average electrical conductivity values were evidently higher than obtained in other parts of the world farther away from the geomagnetic equator. Sq current vortex foci are observed very close to the geomagnetic equator. Depth of penetration was greatly enhanced. Stations on latitudes less than 1° from the geomagnetic equator show higher electrical conductivity when compared with that situated more than 4° away from it at various corresponding depths. Evidence of discontinuities in the earth layers were also noted at some depths. Highly conductive layers were delineated around 400 km depth and beyond 1200 km.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Agbo, G.A. and Okeke, F.N. (2009) Preliminary results from 3-D approach to ionospheric conductivities in the equatorial region. Pacific Jour. Sci. Tech., v.10(1), pp.674–679.
Arora, B.R., Campbell, W.H. and Schiffmacher, E.R. (1995) Upper Mantle Electrical Conductivity in the Himalayan Region. Jour. Geomagnet. Geoelect., v.47(7), pp.653–665.
Banks, R.J. (1972) The overall conductivity distribution of the Earth. Jour. Geomag. Geoelectr., v.24, pp.337–351.
Campbell, W.H. (1987) The upper mantle conductivity analysis method using observatory records of geomagnetic field. Pure Appld. Geophys., v.125, pp.427–457.
Campbell, W.H. (1989) The regular geomagnetic-field variations during quiet solar conditions. In: Jacobs, J. (Ed.), Geomagnetism: Calif, S.D. Academic. no.3, pp.386–460.
Campbell, W.H. (1997) Introduction to geomagnetic fields. Cambridge Univ. Press.
Campbell, W.H. and Anderssen, R.S. (1983) Conductivity of the subcontinental upper mantle: an analysis using quiet- day records of North America. Jour. Geomag. Geoelectr., v.35, pp.367–382.
Campbell, W.H. and Schiffmacher, E.R. (1985) Quiet Ionospheric Currents of the Northern Hemisphere Derived From Geomagnetic Field Records. Jour. Geophy. Res., v.90, A7, pp.6475–6486.
Campbell, W.H. and Schiffmacher, E.R. (1987) Quiet ionospheric currents and Earth conductivity profile computed from quiet-time geomagnetic field changes in the region of Australia. Aust. Jour. Phys., v.40, pp.73–87.
Campbell, W.H. and Schiffmacher, E.R. (1988) Upper mantle electrical conductivity for seven subcontinental regions of the Earth. Jour. Geomagnet. Geoelectr., v.40, pp.1387–1406.
Campbell, W.H., Barton, C.E., Chamalaun, F.H. and Welsh, W. (1998) Quietday ionospheric currents and their application to upper mantle conductivity in Australia. Earth Planet. Space, v.50, pp.347–360.
Chandrasekhar, E. (2011) Regional Electromagnetic Induction Studies Using Long Period Geomagnetic Variations. Chapter 3, in The Earth’s Magnetic Interior, Vol. 1, edited by E. Petrovský, E. Herrero-Bervera, T. Harinarayana and D. Ivers, pp.31–42, Springer Dordrecht Heidelberg London, New York.
Chapman, S. (1919) The solar and lunar diurnal variation of the Earth magnetism. London: Phil. Trans. Roy. Soc., v.A(218), pp.1–118.
Chapman, S., Bartels, J. (1940) Geomagnetism. Oxford Univ. Press, London.
Constable, S.C and Duba, A. (1990) The electrical conductivity of olivine, a dunite and the mantle. Jour. Geophys. Res., v.95, pp.6967–6978.
Didwall, E.M. (1984) The electrical conductivity of the upper mantle as estimated from satellite magnetic field data. Jour. Geophys. Res., v.89(B1), pp.537–542.
Drury, M.J. and Niblett, E.R. (1980) Buried ocean crust and continental crust geomagnetic induction anomalies: a possible association. Canadian Jour. Earth Sci., v.17, pp.961–967.
Dziewonski, A.M. and Anderson, D.L. (1981) Preliminary reference Earth model. Phys. Earth Planet. Inter., v.25, pp.297–356.
Gauss, C.F. (1838) Allgemeine Theories des Erdmagnetismus, in Resultate aus den Beobachtungen des magnetischem Vereins in Yahr, edited by C. F. Gauss and W. Weber: translated from the German by E. Sabine and R. Taylor. Sci. Mem. Select. Trans. For. Acad. Learned Soc. Foreign J. 2: 184–251, 1841.
Gough, D.I. (1983) Electromagnetic geophysics and global tectonics. Jour. Geophys. Res., v.88, pp.3367–3377.
Jackson, I. and Ridgen, S. (1997) Composition and temperature of the Earth’s mantle: seismological models interpreted through experimental studies of mantle minerals. In: The Earth’s mantle, composition, structure and evolution. Edittedbi I. Jackson. Cambridge University Press, London.
Jones, A.G. (1983) On the equivalent of the “Niblette” and “Bostick” transformations in magnetelluric method. Jour. Geophys. Res., v.53, pp.72–73.
Katsura, T. and Ito, E. (1989) The System Mg2Si04-Fe2SiO4 at high pressures and temperatures: precise determination of stabilities of olivine, modified spinet and spinel. Jour. Geophys. Res., v.94(15), pp.663–670.
Maxwell, J.C. (1873) Treatise on Electricity and Magnetism. Cambridge Univ. Press.
Neal, S. L., Mackie, R. L., Larsen, J. C. and Schultz, A. (2000) Variations in the electrical conductivity of the upper mantle beneath North America and the Pacific Ocean. Jour. Geophys. Res., v.105(B4), pp.8229–8242, doi:10.1029/1999JB900447.
Obiekezie, T.N. and Okeke, F.N. (2010) Upper Mantle Conductivity Determined from the Solar Quiet Day Ionospheric Currents in the Dip Equatorial Latitudes of West Africa. Moldavian Jour. Physical Sci., v.9(2), pp.199–204.
Obiora D.N., Okeke F.N. and Yumoto K. (2013) Determination of the crustmantle electrical conductivity-depth structure of Niger Delta using solar quiet day (Sq) current. Internat. Jour. Physical Sci., v.8(7), pp.272–276.
Obiora, D.N. and Okeke, F.N. (2013) Crustal and upper mantle electrical conductivity structure in North Central Nigeria. Internat. Jour. Physical Sci., v.8(42), pp.1975–1982.
Obiora, D.N., Okeke, F.N., Yumoto, K. and Agha, S.O. (2014) Mantle electrical conductivity profile of Niger delta region. Jour. Earth Syst. Sci., v.123(4), pp.827–835.
Onwumechili, C.A. and Ogbuehi, P.O. (1967) Analysis of the magnetic field of the equatorial electrojet. Jour. Atmos. Terr. Phys., v.29, pp.553–566.
Ritz, M. (1984) Inhomogeneous structure of the Senegal lithosphere from deep magnetelluric soundings. Jour. Geophys. Res., v.89, pp.11317–11331.
Rycroft, M.J., Kartalev, M.D., Papitashvili, V.O. and Keremidaska, V.I. (2005) On the effect of near equatorial thunderstorms on the global distribution of ionospheric potential. Adv. Space Res., v.35, pp.1450–1460.
Schmucker, U. (1970) An introduction to induction anomalies. Jour. Geomag. Geoelectr., v.2, pp.9–33.
Schmucker, U. (1987) Substitute conductors for electromagnetic response estimates. Pure Appld. Geophys., v.125, pp.341–367.
Shuster, A. (1889) The diurnal variation of terrestrial magnetism. Phil. Trans. Lond. A180: 467–518.
Web address: http://home.iprimus.com.au/toddemslie/darwin-dxpedition.html.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Ugbor, D.O., Okeke, F.N. Deep earth electrical conductivity-depth profiles around African geomagnetic equator using solar quiet currents. J Geol Soc India 89, 344–350 (2017). https://doi.org/10.1007/s12594-017-0609-8
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s12594-017-0609-8