A geophysical study was carried out in the vicinity of two collapsed and concealed septic tanks to delineate the structures responsible for their failure. Two-dimensional resistivity and seismic refraction tomography data were collected along a profile laid across the septic tanks. The data were collected using ABEM Terrameter SAS 4000, aided with LUND imaging equipment and seismograph, Terralloc MK6 respectively. The data were processed using REFLEX-W and RES2DINV software respectively. Pseudosections obtained show that the vicinity of the septic tanks is characterized by resistivity of 10 5200 m and p-wave velocity of 320 2400 ms-1. Results show that these ranges encompass those of clay and sandy clay at shallow depths, and granite and gneiss in a shallow and undulating basement. The zones where the tanks were apparently sited show very low p-wave velocity of < 600 ms-1 and on the contrary, very high electrical resistivity of >5000 m which suggest the presence of trapped air column. Based on the interpreted results, the tanks are estimated to be with lateral extent of about 6.5 m and depth of about 2.9 m. The delineated clayey soils at shallow depths suggest that there could be seasonal soil swelling and shrinkages due to seasonal variation in moisture content of the clay. These most likely led to annual ground movements, cumulative soil creep and the subsequent collapse of the septic tanks.

Aeromagnetic data obtained from a recent aeromagnetic survey of Sokoto Basin, northwestern Nigeria has been studied using Power Spectral (PS) analysis. The Sokoto Basin is an arm of the Iullemmeden Basin is situated between latitudes 10°30’’ N to 14° 00" N and longitudes 3° 30” E to 7° 00" E in the Nigeria national grid. The PS analysis was carried out to determine the depth to magnetic sources in the Basin. By splitting the study area into 16 spectral model blocks, the spectral probe of 27.5 by 27.5 km2 for each block was carried out respectively. The results of the PS analysis revealed two prominent magnetic source depth layers. Depths determination of the magnetic sources showed that the first layer has average depth of 0.28 km which is interpreted as shallow magnetic zones attributed to the intrusions of magnetic rocks into the sedimentary formation. The second layer has average depth of 1.86 km and was interpreted as the deep magnetic source representing the depth to magnetic basement. Hence the results show that the maximum thickness of the sedimentary layers to be 1.86 km is the limit of the depressions on the basement surface of the basin. Hence it suggests that exploration of hydrocarbon which would require a minimum sedimentary thickness of about 2.3 km as obtainable in the coasts of West Africa region is also not feasible.

Two dimensional (2D) modelling of the subsurface lithology in the subsurface of Sokoto Basin, north-western Nigeria has been carried out using the area's aeromagnetic map. The modelling was aimed at investigating the potentiality of the area for mineral exploitation especially hydrocarbon even as a sedimentary and marine environment. The Basin covers an estimated area of 59,570 km 2 which falls within .° by .° in Nigeria national grid. Three survey straight lines trending NW-SE and cutting across some anomalous zones in the area's residual aeromagnetic map were selectively drawn for the modelling and interpretation. With the aid of GM-SYS Software Version 2.5D, the two dimensional models of the subsurface sediments and basement rocks. The results of the modelling showed that the area characterized by Cretaceous sediment of single lithology in the range of about 250 m to 400 m thick. The resulting model also showed a magnetic basement characterised by various lithology of rugged topography, dipping north-westwards of the study area. The interpreted model of the basement comprises igneous rocks such as Gabbro, Granite, Andesite, Schists, Rhyolite, Pyroxenite, Phylites, and Esites. The sediment-filled troughs and depressions on the basement's surface suggest that they could be good targets for groundwater. Also, several solid minerals could be exploited based on the modelled multi lithology magnetic basement. However, the maximum depth to the basement troughs suggests that the requirements for formation of hydrocarbon have not been met in the area; therefore its exploitation is not feasible in the Basin.

Two-dimensional Electrical Resistivity Tomography (2DERT) and Seismic Refraction Tomography (2DSRT) were concurrently applied in assessment of a gully site with the view of assessing its stability and risk level. Eight profile lines oriented parallel and perpendicular to the boundary of the gully were surveyed. As a result, apparent resistivity model tomograms in the range of 1-9,000 and p-wave velocity models in the range of 300-700 were obtained from the two techniques respectively. Interpretation of the models obtained show predominance of unconsolidated clay, shale intercalates, clayey sand, sandy clay and weathered lateritic soil at shallow depths. Low amplitude undulating refracting layers, landslide slip subsurface and lose horizons were also delineated at shallow depths. The predominance of weak, clayey and unconsolidated lithology at the gully site suggests evidence of unstable gravitational equilibrium which imply environmental hazard. The plausible deductions made from the two