A magnetic survey of local gravity, highs in magadi area

Abstract

Magadi area is located in the southern part of the Kenya. Rift, an active continental rift that is part of the East African Rift system. Thermal manifestations in form of hot springs in northern and Southern shores of lake magadi and high heat flow suggest geothermal potential in the area. The area is highly characterized by grid faults, which allow escape of underground water as hot springs.

A ground magnetic survey have been carried out in this area as a follow -up to investigate whether the known gravity highs at Magadi mapped in the Kenya Tertiary Rift study are related to a heat source responsible for the numerous hot springs. The vertical magnetic field intensity has been measured with a flux-gate magnetometer with an accuracy of nThe field has been corrected for both the diurnal and geomagnetic variations and the residual anomaly isolated from the regional. Positioning was carried out by use of a Global positioning system device. With the reduced magnetic data regularized in a rectangular grid, a contour map was computed to obtain the intensity of the field. Qualitative and quantitative interpretations have been made from the reduced vertical magnetic intensity contour map of the area. Qualitative interpretation involved discerning anomalous regions in the study area from the contour map of the reduced vertical magnetic intensity.

Quantitative interpretation involved both direct interpretation and forward modelling along three selected profiles. The causative bodies are interpreted to have prismatic shapes suggesting them to be dikes. Interpretation involved fitting a calculated model of a thick sheet assuming uniform magnetization to the observed data by computer iterations. Magnetic bodies at depths of 1 km, 0.9 km and 1.0 km with widths of 2.2 km, 3.5 km, 1.5 km and 1.0 km. Their dips are 78o, 40o, 60o and 105o with strike directions as 150o, 83o, 144o and 144o respectively. The depths to the bottom of bodies are 1.99 km, 4.09 km, 3.0 km and 2.9 km respectively. These depths to the bottom where the bodies cease to be magnetic are considered shallow suggesting the depths to represent Curie point depth. The models obtained are considered reasonable as they match well with the geology of the area with other geophysical studies that had been carried out in the research area.