Surface and Subsurface Structural Mapping of Lokoja Central Nigeria Using Airborne Magnetic and Remote Sensing Data

Abstract

The main goal of this research is to evaluate the surface and subsurface structural framework of Lokoja and its surroundings using airborne magnetic and Shuttle Radar Topographic Mission (SRTM) data by applying image processing techniques. To explicate our aim, the residual magnetic intensity (RMI) data was reduced to a magnetic pole (RTP) to centre the anomalies above their causative source after which, the data was subject to the first vertical derivative filter and 3D Euler deconvolution method with structural index (SI =1) where the subsurface structures were delineated, using Oasis Montaj software. Four (4) shaded relief images were created with light sources emanating from four different directions to identify linear terrain features in the SRTM data at a solar azimuth of 0° and a solar elevation of 45°. Others 90°, and 135° followed by creating a composite shaded relief image of all four. The PCI Geomatica edge detection algorithm was applied to the composite shaded relief image produced. After thresholding and filtering processes, structural lineaments were extracted from the edges of the image by subjecting it to the line algorithm of PCI Geomatica.  ArcGIS v10.7.1 was used to assign geometry to both magnetic and SRTM structures delineated. The resulting structural lineaments were subjected to Rockworks where a rose diagram that depicts structural trends within the study area was produced. The lineaments delineated allow us to decipher that the area is dissected by numerous subsurface and surface linear structures and these lineaments trend predominantly in the NE-SE, WSW-ENE, NW-SE, and NNE-SSW directions. Overlying the lineaments drawn from the pair of data sets showed several sites of structural coincidence that are thought to be structural continuation locations where subsurface fluids such as water will migrate directly to the surface.