Determination of the crust-mantle electrical conductivity-depth structure of Niger Delta using solar quiet day (Sq) current

Abstract

Innovative attempt has been made to study the crust-mantle electrical conductivity-depth structure of the Niger Delta region in Nigeria by applying solar quiet (Sq) day current. The study involved the use of geomagnetic data obtained from Lagos by magnetic data set (MAGDAS), Japan in 2010. Gauss spherical harmonic analysis (SHA) technique was employed which separated the internal and external field contributions to Sq current system. The result revealed that the conductivity-depth structures could be determined using Sq current systems. The conductivity-depth profile started from 0.004 S/m at a crustal depth of 300 m and increased sharply to 0.178 S/m at 1 km depth. It then started decreasing until it got to 0.021 S/m at sub-crustal depth of 44 km. The profile then rose steadily from 0.041 S/m at 100 km to 0.09 S/m at 221 km. It continued increasing downward until it got to 0.211 S/m at 888 km depth and reached 0.243 S/m at a depth of 1179 km at the lower mantle. The downward increase in conductivity agrees with the global models which depicted a steep rise in conductivity from 300 to 700 km. Key words: Crust-mantle, conductivity-depth structure, electrical conductivity, Niger Delta, solar quiet (Sq) day current, spherical harmonic analysis (SHA).