Geological preconstruction assessment of the proposed site for Layifa housing estate, Jigawa State, Nigeria from aeromagnetic data

Abstract

Preliminary geological preconstruction assessment of a proposed housing estate site in Jigawa State, northern Nigeria has been done from analysis of aeromagnetic data for the purpose of optimised physical planning, particularly in the area of forestalling any potential risk that may be associated with the existence of linear geological structures or sub-surface conditions that may be inimical to engineering structures. The techniques adopted for the data enhancement include the total horizontal derivative, second vertical derivative and Euler deconvolution solutions. Spectral analysis was also performed on the data to determine depth to the magnetic basement rock, hence overburden thickness and basement topography. Data enhancement analyses delineated considerable number of semi-regional to regional-scaled lineaments, the existence of which presented the study area as a suspected shear zone. Basement topography was found to be highly rugged with evidence of rift-controlled subsidence detected in the eastern section. Having just a few lineaments traversing through it and being located where the basement topography is relatively less undulating, a trapezium-shaped area in the central southern region was identified as the most stable location within the study area, geologically. Two unmapped geologic bodies were delineated from the magnetic data as well. Drilling efforts confirmed an initially unmapped quartzite at the location where one of the two unmapped bodies were delineated and this validated the potency of magnetic data as an aid for geologic mapping. If established that lineaments F25, F26 and F28 traversing through this area are not seismically active, the trapezium-shaped area, said to be least affected by geological factors, could be used for building constructions. However, it is advised that high-rise buildings should not be concentrated in the area but cascaded buildings are recommended due to the fact that a portion of the area is located on a hill-slope and the topography of the basement rock underneath is also coincidentally sloppy. The study area was found to be a shear zone with highly undulating basement topography. Therefore, construction on the site must be approached with caution.