SUBSURFACE MAPPING OF LOW VELOCITY LAYERS WITHIN THE SUBSURFACE USING SEISMIC REFRACTION TOMOGRAPHY: A CASE STUDY OF OSUBI CAMPUS, SOUTHERN NIGERIA

The accurate mapping and characterization of low velocity layers within the subsurface are essential for various applications, including resource exploration, geotechnical engineering, and environmental assessment. Traditional seismic methods often face challenges in detecting and resolving these layers due to their complex geological properties. This thesis aims to enhance the accuracy and reliability of subsurface mapping of low velocity layers using seismic refraction tomography. A comprehensive literature review was conducted to identify current methodologies and technological limitations in seismic refraction tomography. Advanced inversion algorithms were developed, incorporating machine learning techniques to improve resolution and accuracy. Field surveys were designed and implemented to acquire high-quality seismic data from diverse geological settings, followed by rigorous preprocessing and quality control protocols to enhance data quality. The result obtained from the tomographic models indicates that the top soil (Figure 4.9 – 4.10) which is highly weathered extended to a depth of 4m below the surface. The overburden thickness which comprises the top soil and the weathered layer is about 10.05m, which also stands as the depth to weathered basement. The depth to the fresh basement is about 18.09m, thereby giving the thickness of the weathered basement as 8.04m. The lithology analysis revealed that the top soil and the weathered layer is made up of laterite and silty clay, the weathered basement which is the aquifers, is made up of pebbles and gravels, while the fresh basement is composed of coarse sand.