Aeromagnetic Interpretation of Basement Structures and Geometry in Parts of the Middle Benue Trough, North Central, Nigeria

The research of an analysis of aeromagnetic data collected in the middle Benue Trough in north-central Nigeria is presented. A detailed analysis of basement structures is conducted in order to identify regions with high hydrocarbon potential that is different from those discovered by earlier researchers. Aeromagnetic data were filtered by using the Butterworth and Gaussian filters, transformed by engaging the reduction to the equator technique, and subsequently enhanced. To estimate magnetic basement depths at various places throughout the basin, the Euler deconvolution depth weighting approach was used. Eleven (11) sub-basins with depths ranging from –2000 m to –8000 m were also identified by Euler’s findings. The sub-basins trend in the NE-SW direction while the average sediment thickness is found to be more than 3 km. The extracted structural features indicate areas like Kadi Blam and Kado areas in the southeastern part and Ogoja and Obudu in the southern part of the study area as regions with high structural densities. These areas coincide with the areas delineated as the sub-basins. The cross-sections generated reveal depressions caused by the action of some tectonic activities in the area. This study identified undulating basement topography believed to be due to tectonic activities as well as five areas that are possible targets for hydrocarbon exploration

Retrospective and forward prediction of next strong earthquakes in oceanic ridges and trenches using probabilistic models

Earthquake occurrence and recurrence depend on number of factors beyond mere observations. These include seismotectonic nature of the region, spreading rate of the ridge or subduction of plates causing the trench, active or otherwise nature of the fault on crust (on land), stress‐strain regime, and so on. In this work, the recurrence and expected times of next strong earthquakes (M ≥ 6) in the oceanic ridges and trenches were computed using gamma and lognormal probabilistic models. Summing the occurrence times of last strong earthquakes and these recurrence times, expected times of the next strong earthquakes were retrospectively and forwardly predicted. The expected times of the next strong earthquakes retrospectively predicted correlated with the recorded strong earthquakes in the earthquake catalog of the Advance National Seismic System (ANSS) hosted by the Northern California Earthquake Data Centre, USA, for the period of 1978–2017 in a readable format. The successful prediction of the expected times of the next strong earthquakes retrospectively is an indication that the expected times of the next strong earthquakes forwardly predicted in the regions of study will be positive. However, since the occurrence and recurrence of earthquakes depend on many factors, it is therefore important to note that it may not always be accurate to predict future earthquakes from retrospective perspective. Nonetheless, this work is a good effort, and it has thrown up some interesting results

Direct current electrical resistivity forward modeling using comsol multiphysics

Forward modeling of direct current (DC) resistivity is very important for the inversion of the resistivity data to obtain the true resistivity of the subsurface. In this study, we demonstrated finite‐element forward modeling of DC resistivity method with point electric source using COMSOL Multiphysics. We employed the AC/DC module in COMSOL which often provides comparatively easy implementation of models and permits exterior boundaries to be placed at infinity, a boundary condition often experienced in most geophysical problems. The validity and effectiveness of the results of numerical simulation using COMSOL Multiphysics were evaluated by comparing the output of the numerical simulations with the calculated analytic solutions. The result reveals that the numerical simulation is in agreement with the analytic solution. This study shows that COMSOL Multiphysics can be used to simulate the distribution of electrical potentials of point source in 3D space in real life and the information from this study can be used for further studies, such as DC resistivity inversions

Evaluation of global seismicity along Northern 1 and Southern hemispheres

An earthquake has been identified as one of the major natural disasters that cause loss of lives and property. To mitigate this disaster, knowledge of global seismicity is essential. This research is aimed at evaluating the Gutenberg Richter b-value parameter and focal depth distribution of earthquake parameters to identify the prominent earthquake-prone zones in the Northern and Southern hemispheres. The study area covers 20° to the Northern and Southern hemispheres, with the equator in the middle. The data were obtained from the earthquake catalogue of the Advanced National Seismic System (ANSS) hosted by the Northern California Earthquake Data Centre USA from 1963 - 2018. Fifty-four-year earthquake data of M 6.0 were processed and analyzed using Gutenberg- Richter (GR). The b-value parameters obtained from the GR model were plotted against the hemispheres using bar chart graphs to determine the tectonic stress level of the study region. The earthquake energy released was evaluated along the Northern and Southern hemispheres for a proper understanding of seismic events in the study region. It was observed that the rate of earthquake occurrence at the Southern hemisphere is higher than the Northern hemisphere. The b-values obtained in all the zones vary from 0.82 – 1.16. At the same time, the maximum earthquake energyof 4.6 × 1025 J was estimated. Low b-values indicate high tectonic stress within the plates. The large tectonic stress accumulation around the equator suggests that unstable lithospheres characterize this zone

Analysis of principles of equivalence and suppression in resistivity sounding technique

The principles of equivalence and suppression in resistivity sounding technique are phenomena where different resistivity models may produce resistivity curves that are essentially the same. The understanding of these phenomena could be of great importance in using resistivity sounding technique for citing boreholes in places underlain by Basement Complex rocks. In such areas, it would be difficult to identify the fractured/weathered bedrock from the sounding interpretation. This is because the resistivity of the weathered layer is usually intermediate between those of the adjacent layers (i.e. residual overburden) on top and the fresh bedrock below. Therefore, it is important to analyse the problems of suppression and equivalence in resistivity sounding data for estimating thickness and resistivity of the subsurface layers. Several resistivity models were generated ranging from two-layer to five-layer models to investigate these phenomena. The apparent resistivity curves were plotted for these models. The results show that the problems of suppression and equivalence exist in resistivity sounding data. Hence, geophysicists should not make any a priori quantitative inferences using the shape of the resistivity sounding curve

Understanding the interrelationship between electrical anisotropy and groundwater yield in a typical Basement Complex area

The rocks in the Basement Complexof southwestern Nigeria exhibit electrical anisotropy as a result of their heterogeneous nature caused by weathering, near-surface effects or presence of fractures. It is known that groundwater yield (Y) in a typical Basement Complex aquifers is related to its coefficient of anisotropy (). Therefore, it is essential to study the correlation between Y and in the basement complex. Ten (10) vertical electrical sounding (VES) points using Schlumberger array were studied in areas underlain by migmatite gneiss and quartzite rocks. The current electrode spacing (AB/2) varies from 1 m to a maximum spread length of 100 m. The quantitative interpretation of VES curves was done by using partial curve matching and computer assisted program called WinResist version 1.0 software. Dar Zarrouk parameters were estimated from the interpreted VES curves and thus coefficient of anisotropy () was calculated from these parameters. Data on the groundwater yield at the VES points were also obtained. The results show that as increases, Y also increases with coefficient of correlation (R2) of 0.86 and 0.79 for migmatite gneiss and quartzite rocks respectively. To further investigate the relationship between Y and, a regression analysis was performed. The regression analysis that was performed on the dataset shows that contributes significantly to the regression models of the two rocks. The relationship between Y and reveals that groundwater yield could be predicted from the values of in a given locality