Geothermal Prospecting of Olkaria Dome Areas in Naivasha, Nakuru County Kenya Using Gravity Method

Abstract

he survey used Autograv.C.G 5 type Gravimeter over short wavelength by marking stations 310m intervals. The data was processed to remove all other effects independent of the subsurface changes in density. The complete bouguer anomaly was computed and Surfer 11 software has been used to draw contour anomaly map of the study area. Quantitative analysis of the contuor map indicates regions of gravity highs which were analysed as bodies of high density within the earth’s crust. Four profiles were drawn. The gravity anomaly was interpreted by inspection of profiles and separating the residual anomaly from the regional gravity field. 2D Euler deconvolution was done on the data profiles, indicated subsurface bodies and faults at depth between 10m and 50m. A 2D gravity model along the four profiles were generated by the computer application based on algorithm in the Grav. 2dc.The obtained results revealed presence of dense body intrusions with the contrasting density ranging from 0.22g/cm3 to 0.50g/cm3. These bodies were interpreted as intrusive dykes that have higher density than surrounding rocks and probably are conduits of heat from the geothermal reservoir imaged at bottom depth of between 500m – 1000m below the surface. Advance methods of gravity data analysis such as Tensor Euler deconvolution is recommended to be carried out in Olkaria Domes to verify the results since this technique hoonours responses from many dimensions and deconvolution without gridding. Collection of more gravity data over steep and wild animal habitat areas is also required for deeper probing on longer profiles.