Results from magnetic field modelling of the Lower Benue Trough, West Africa revealed thick sedimentation with maximum values in the neigbourhood of 7,000m-10,000m. This is in contrast to the average value of 5000m suggested by earlier studies. The thick sedimentation represent thermal sag which is a regional post-rift subsidence associated with West and Central Africa rift systems. N-S, NNW-SSE and E-W structural fabrics interpreted from the transformed magnetic data bound the trough. The subsurface magnetic models also revealed extended graben structures that form the major depoceters that are segmented by intrarift horsts and average crustal thickness of 22km. The qualitative interpretation comprising, analytic signal, directional derivatives and wavelength filtering in frequency domain and subsurface magnetic modelling show that the rift architecture/geometry is controlled by high angle faults and some sinistral transtensional movements that are predominant in the Benue rift system. The low mean anisotropic susceptibility (kb =-6.7x10-4 SI) correlating with the directional horizontal derivative (dy) of the magnetic field conform with the sinistral movement in the trough indicating that magnetic anomalies align themselves along fractures/faults/shear zones owing to their variations in physical properties. The characteristics/patterns of the magnetic anomaly wavelength and inferred results from earlier studies on geophysical potential field methods, geological investigation and physical parameters (susceptibility and remanence) obtained from the subsurface magnetic modelling are pointers to non-magmatic origin of the Lower Benue Trough. The basement structuring, basin framework and predominance of anisotropic susceptibilities (ka, kb and kc) in three orthogonal directions and remanence suggest tectonic setting in the trough due to Early Cretaceous opening of the South Atlantic Ocean and interplate movement in Africa. The grabens, half grabens, faults and deep sedimentation (depocenters) interpreted from the magnetic data are hydrocarbon related structural features.

Geoid undulation has been determined for Nigeria in order to demonstrate its relationship with topography and the dynamic structure of the Earth’s interior. Spherical harmonic expansion using the Earth Gravitational Model 2008 (EGM2008) referenced to the WGS84 (World Geodetic System 1984) with coefficients extending to degree 2190 and order 2159 was found suitable for the determination of geoid undulation. The results from the analysis show that the Nigerian geoid undulations are positive and show overall good correlation with topography. The internal origin of the geoid undulation is attributed to excess mass beneath the ellipsoid. This internal mass distribution extend deep into the mantle. The highest geoid undulations are centered over the North central region of Nigeria with relatively lower values confined to the Nigerian sedimentary basins. The lowest geoid undulation values are within the oceanic areas.

The drift characteristics specific to an unstable gravimeter has been modeled to enhance high quality data that will be useful for gravimetric studies and to determine proper timing of field observations. A pre-field observation was carried out to monitor the tide and thus limiting the relative gravity observation to near-linear time window. Closed loop sequence technique of re-occupying a drift base compatible with the drift characteristics of the Lacoste and Romberg (model G446) and cascade model for the computation of drift were combined to obtain a more reliable data that fulfills the linear drift assumption. Subjecting the modelled drift to descriptive statistics a maximum value (1.6550mGal) and minimum value (-0.3720mGal) of drift were obtained. This variability in drift values and the disparity between the mean (0.099mGal) and the standard deviation (0.2914mGal) is a pointer to various factors that caused the instrumental drift. Such factors could be attributed to external temperature, age and usage of the gravimeter, mechanical stress and strain in the mechanism as the gravimeter is moved and subjected to vibrations. The low standard error of the mean (0.0196mGal) is a reflection of the validity of the linear drift assumption using the cascade model and the field procedure compatible with the drift characteristics of the gravimeter.

Aquifer positions were determined by using Schlumberger electrode configuration to conduct Vertical Electrical Soundings in 67 communities within the study area. This study was carried out because of the presence of failed boreholes and manually dug wells in some of the Local Government Areas in the study area. More précis information relating to the exact location of aquifers is therefore needed for successful management of water resources in the area, in the face of dwindling availability of portable water, occasioned by failed boreholes and the need to carter for the increasing population of inhabitants of the area. Interpretation of data showed two to six geoelectric layers. Reflection coefficient and resistivity contrast values greater than 0.9 and 19 respectively, were obtained in some VES stations. Productive shallow and deep aquifer terrains were identified with depth of 60 m and 150 m respectively and resistivity range of 100.0-500.0 Ωm for shallow aquifers and 1000-2500 Ωm for deep aquifers, respectively. The lithologic materials for the aquifers were sand/sandstone and very coarsed grained sand/fractured basement, respectively. The above inference on lithology was constrained by borehole logs in the study area.

Directional horizontal derivatives, analytic signal, filtering of magnetic data sets and 3D magnetic modelling incorporating induced and remanent magnetization were performed on low resolution aeromagnetic data to unravel the basement structure and its relationship with hydrocarbon target offshore Niger Delta basin. Forward modelling of the residual magnetic data gave discrete depth values that were exploited to compile the depth to basement (thickness of the sedimentary section) map which highlighted deep depocenters, high blocks and major sedimentary fairways in the study area. The uplifted blocks created the arches while downdropped ones produced the depocenters. The depth to the basement map revealed basement paleotopography which resulted from movement along fault zones. The transformed/enhanced data revealed three potential stress regimes trending NE-SW, N-S and E-W. The NE-SW lineaments are shear zones, more dominant and indicate possible extensions within the African continent of Charcot and Chain oceanic fracture zones. The E-W lineaments are revealed not only in the enhanced maps but also in the total magnetic intensity and residual data sets because they are associated with dykes. The N-S structures are very subtle and are therefore highlighted only in the transformed data. In combination with the E-W structures they are brittle and reactivated structures associated with faults and have significant implications for the tectonic evolution of the Niger Delta and its basin extensions. The transformed data sets, depth to basement map and residual data strongly suggest that jostling of the basement blocks has influenced deposition in the Niger Delta basin. The structural highs (basement highs), basement lows (structural lows) and steep/faulted basement flanks are attractive sites for oil and gas accumulation.