Electrical Conductivity Profile of upper mantle in the West African Sub region

Abstract

Authors: T. N. Obiekezie^l and F. N. Okeke

This study used for selected geomagnetic field records and established the 1993 quiet day current system (Sq) for West Africa and used the ionospheric current source of Sq for a determination of the Earths upper mantle electrical conductivity. The magnetonzeter data obtainedfrom a chain of 10 geontagnetic stations installed in the African longitudes during the IEEY 1993 experiment was used. A spherical hannonic analysis (SHA) allowed the separation of the internal and external field contribution to the Sq variations. A special transferfunction allowed the computation ofthe conductivity — depth profile for West Africa from the paired external and internal coefficient ofthe SHA. A regression line fitted to the data points enabled us to get an average ofvalues the ntany scattered individual depth-conductivity determinations. It was interestingly observed that conductivity profile rose rapidly front 0.037 Shn at a depth of 100knz to about 0.09 Shn at 205km.The profile then rose steadily till it got up to 0.15 S,4n at 476 km at the transition zone, it continued to increase gradually until it got to 0.2 S/m at 880 km and 0.22 Shn at 1200 km, at the lower mantle. Our results seemingly, are in consonance with the results obtained in the Hünalayan region and in Australian region. The high conductivity values are in agreonent with the earlier results obtained in the South African region.