Use of magnetic method in identification of faults and underground structures, case study Olobanita well field Nakuru Kenya

Abstract

Nakuru town the fastest growing town in Africa, with high population growth brought about by rural urban migration and high birth rate. This has lead to escalating water demand and setting up of well fields as Olobanita and Baharini was vital to cope up with the increasing water demand in the study area. But the collapsing of boreholes and low yields in the well field is a major concern and investigation to its causes has to be carried out to avoid such repetition in the future. Understanding the geology and underground structures is thus very important in knowing the causes and ways to curb such occurrences in the future. The project looks on the application of magnetic method as a mapping tool for determining subsurface structures as faults which control and influence ground water movement and occurrence. The main objective of the study will be to analyse existing magnetic data and be able to interpret structures and faults found within the well field. The magnetic principle had to be understood well before application of magnetic method as a mapping tool. The data was interpreted using Euler deconvolution method and plotted using Oasis montaj softwares which gave contoured magnetic maps of the study are. Euler deconvolution was implemented for analysis of magnetic data to establish depth to magnetic sources along the different profiles. From profile analysis we observe that magnetic sources range from 20 meters to depth of about 200 meters in some profiles, while others range to maximum depths of only 70 meters. It was concluded that the magnetic sources found at this depth are caused by the volcano sedimentary rocks which may have been oxidized hence the anomalies. It was also concluded that normal faults are found in the study area. After using different filter methods, other minor faults were found which run North-West to South-East. The collapse of borehole X was attributed to high clay and silt content found along the fault zone where the borehole was located. It was recommended that special drilling mud be used when drilling in such areas to curb the collapse of such borehole and the use of software as Geographical Information System (GIS), Euler deconvolution and Oasis montaj be introduced during undergraduate.