A gravity survey of the Longonot-Suswa area

Abstract

The area of study comprises a part of the Rift Valley which has geothermal potential. The gravity prospecting method was used in the project to investigate the anomalies occur in the area. Qualitative and quantitative interpretations were attempted and conclusions drawn from the findings. A gravity survey was conducted to "fill-in" the unsurveyed sectors. After applying the necessary corrections to the field data, digital filtering was applied. The filtering helped to remove or significantly attenuate the geologic noise. Bouguer anomaly maps of the area were then drawn. The filtered data reliably indicate geological structures of interest. The Bouguer gravity values range from-208 to -156mgele with the minimum peak occur directly above the Longonot volcano. Other anomalies occur at Buni and the HeIle Gate in the Ol'Njorowa gorge. The relationship between location of the gravity anomalies and the topographic features of the area is clearly noticeable. The quantitative interpretation involved fitting theoretical three-dimensional models to the observed data along profiles. The choice of three-dimensional models was dictated by the shape of the anomalies to be interpreted. The anomalies were interpreted in terms of intrusions of several bodies. A density of 2.0 gcm-3 was used for the intrusive bodies. The geometries of these bodies were also determined. Two of the most striking feature e which were interpreted are the "bum" and the "crater" dykes. The study of the anomalies indicated that the major gravity disturbances were caused by the rifting and the subsequent tectonic activities. The agreement between the final geophysical model with the characteristics of the known geology shows that the model is reasonable.