Magnetotelluric (MT) Investigation at Nairobi

Abstract

A short historical introduction of the Earth's electrical conductivity studies is presented. A brief review of early and reoent conductivity studies is given, and the results obtained by different methods of conductivity measurements from various plaoes (including Africa) are discussed. The Earth's main conductivity regions based on the general conclusions by different workers are described. The basic theories and equations of the magnetotelluric

method are reviewed. Simplified electromagnetic induction equations are given and the basic techniques of the magnetotelluric sounding according to Cagniard's formulation are discussed. The magnetotelluric instrlunentationsystem used at Nairobi is described and methods of'data aequisition of the station are presented. Finally the experimental results are fully described and discussed. The statistical analysis for obt~ning Fourier coefficients is described and the resistivity profiles obt~ined at the intervals of 6 x 102 - 1055 or (10-5 - l.~~ 10-3Hz) are interpreted according to.Cagniard's -", ~- " method in terms of a three-layer Earth model.

The possibility of ultimate conducting level is estimated to be 170 km depth at Nairobi. Kenya.