Spectral Analysis of Aeromagnetic Data of the Lake Eyasi Basin

Abstract

The Lake Eyasi basin is among the asymmetrical and extensional spoon-shaped rift basins that have developed along the eastern arm of the East African Rift System (EARS). It is bounded by two major fault systems which trend in NE and NW directions. 

This study presents spatial distribution of thickness of sediments filling the Lake Eyasi basin as determined from spectral analysis aeromagnetic data. The data used was acquired during the regional airborne geophysical survey conducted in l976-1980 by Geo-survey International. The method estimates the mean depth of the interfaces considering the log of power of the magnetic spectrum as a function of wave number/frequency assuming uncorrelated distribution of sources. The slopes of regional and residual component were determined by drawing straight lines through well defined linear segments of the curves from which the depths were calculated using the slope relationship.

The magnetic signals arise from sources of magnetic anomalies depending on their depth of burials from the surface. Shallow structures have depth average of 0.7 km which corresponds to shallow greenstone belts and lithological contacts whereas deeper structures were found to have an average depth of 2.3 km. The spectral analysis of aeromagnetic data revealed maximum thickness of 5 km of sediments in south-western portion of Lake Eyasi and a 2.5 km thickness of sediments to eastern part of the basin. In parts of Manonga and Wembere basins, sediments were found to have thickness of 3.5 km and 3 km respectively.

Spectral depths obtained over the Eyasi basin if reflecting sediment thickness suggest prospective basin for hydrocarbons.