Mapping Geological Structures in Western Mutomo, Kitui County: A Remote Sensing Approach
Lineament mapping constitute a very important process in the field of Geology and Earth Sciences. Much of the exploration work, mapping and the exploitation of natural resources including oil and gas, ground water and other hydrocarbons rely on a thorough understanding of the geological structures within an area and the ability to interpret the result from analysis before the exploitation process begins. This increases success rates while reducing cost and time associated with geophysical surveys. Structural analysis and mapping in this study was done using remote sensing and GIS technologies to map linear geological features or structures using optical Landsat data. The analysis was conducted on the multispectral Landsat ETM+ image captured in the year 2001 representing the Southern areas of the Kitui County on the eastern parts of Kenya. This was done in combination with other datasets like DEM, topography dataset, geology and elevation data in order to enhance the understanding and interpretation of structures. Several filters were used to extract lineaments and structures applied on individual subsets of panchromatic bands 4 and 7, the ratio of bands 3 and 4 and the composite image consisting of all the 7 bands in the Landsat ETM+ image. Erdas Imagine® 2013 was the preferred software for this study for conducting image analysis because of its robust filtering algorithms suitable for lineament mapping. The filters applied to the several bands therefore, helped in extracting structures and identifying their trends using several image enhancement techniques like the Linear, Gamma, Gaussian and histogram equalizer and the statistical approach of principle component analysis which uses the covariance of spectral bands to analyze spectral patterns associated with structures in the study area. The DEM was processed for topography and establishing the intersection between tilted plates which helped in recognizing different structures. The interpretation process involved correlating drainage, vegetation patterns and topography of the area with structures using visual interpretation elements of texture, color, tonal differences and orientation. The color and pattern of the geology and geomorphology of the area were also used to infer the different types of lineaments. The output was a structural map representing the different lineations present in the area. The results were validated against sample data collected together with field observations.