Geoelectrical characterisation of basement aquifers: the case of Iberekodo, southwestern Nigeria

Basement aquifers, which occur within the weathered and fractured zones of crystalline bedrocks, are important groundwater resources in tropical and subtropical regions. The development of basement aquifers is complex owing to their high spatial variability. Geophysical techniques are used to obtain information about the hydrologic characteristics of the weathered and fractured zones of the crystalline basement rocks, which relates to the occurrence of groundwater in the zones. The spatial distributions of these hydrologic characteristics are then used to map the spatial variability of the basement aquifers. Thus, knowledge of the spatial variability of basement aquifers is useful in siting wells and boreholes for optimal and perennial yield. Geoelectrical resistivity is one of the most widely used geophysical methods for assessing the spatial variability of the weathered and fractured zones in groundwater exploration efforts in basement complex terrains. The presented study focuses on combining vertical electrical sounding with two-dimensional (2D) geoelectrical resistivity imaging to characterise the weathered and fractured zones in a crystalline basement complex terrain in southwestern Nigeria. The basement aquifer was delineated, and the nature, extent and spatial variability of the delineated basement aquifer were assessed based on the spatial variability of the weathered and fractured zones. The study shows that a multiple-gradient array for 2D resistivity imaging is sensitive to vertical and near-surface stratigraphic features, which have hydrological implications. The integration of resistivity sounding with 2D geoelectrical resistivity imaging is efficient and enhances near-surface characterisation in basement complex terrain

SUBSOIL CHARACTERIZATION USING GEOELECTRICAL AND GEOTECHNICAL INVESTIGATIONS: IMPLICATIONS FOR FOUNDATION STUDIES

Electrical resistivity tomography (ERT) has been combined with geotechnical techniques such as cone penetrating tests, standard penetrating test and laboratory tests for detailed characterization of near-surface strata. This approach can be very helpful in conducting preliminary investigations towards a robust foundation design at a building construction site. Two ERT lines were conducted for 2D geoelectrical resistivity measurements using Wenner array configuration in combination with four cone penetrating data. Through the inversion of ERT data, two geoelectrical layers were interpreted to be loose silty sand and compacted clayey sand lithological units with the resistivity values ranging 50 - 280 ohmm and 10 - 74 ohmm respectively. A water-saturated portion with resistivity values <=3 ohmm due to lagoon-water incursion was equally observed at the base of the second clayey sand layer in ERT line T2. The average cone penetrometer (CPT) value of about 110 kg/cm2 (11 MPa) with an average SPT ‘N’ value of 25 was measured between 6.75 - 30.0 m, indicating that the geomaterials within this depths range are of good geotechnical properties. Laboratory tests conducted on the representative soil samples at 3.75 m depth gives a moisture content (MC) of 66%. This is attributed to the clay contents within the soil samples. The Liquid Limit (WL), Plastic Limit (WP) and Plasticity Index (PI) tests of the soil samples gives 84%, 30% and 54% respectively. The results of the proposed approach, encompassing both geophysical and geotechnical methods has helped to steer the choice of the foundation for the investigated building towards a pile-type foundation rather than a shallow one. The pile foundation will cause the higher loadings to transmit the loads to a stable soil layer within the subsurface

Economics of bio-fortified cassava varieties (BCVs) adoption and its gender implication among farmers in Oyo State, Nigeria

Cassava bio-fortification is presented as a cost-effective approach, and it is predicted to provide some economic benefits to its adopter. On the other hand, gender-blind agricultural innovation delivery strategies impede short- and long-term impact among adopters. Due to a disregard for gender differences, many agricultural programs fall short of their objective. Recent studies in Nigeria are yet to adequately capture the gender differentials in the economic implication of BCVs adoption. This study, therefore, investigates the gender differentials in the economic implication of BCVs’ adoption among farmers in Oyo State, Nigeria. A multistage sampling procedure was used to select a total of 180 respondents for the study. Data collected were analyzed using descriptive statistics and budgetary techniques. Descriptive statistics revealed a significant difference between the socio-economic characteristics of male and female cassava farmers. The results suggested that BCVs’ production is profitable and can serve as a panacea for the economic improvement of households. Study findings thus concluded that the adoption of BCVs is economically beneficial to cassava farmers and thus recommended that concerted efforts are made to ensure all farmers adopt BCVs for planting. The study proposes an integration of gender-responsive strategies to further enhance the delivery of BCVs in Nigeria

Geostatistical exploration of dataset assessing the heavy metal contamination in Ewekoro limestone, Southwestern Nigeria

The dataset for this article contains geostatistical analysis of heavy metals contamination from limestone samples collected from Ewekoro Formation in the eastern Dahomey basin, Ogun State Nigeria. The samples were manually collected and analysed using Microwave Plasma Atomic Absorption Spectrometer (MPAS). Analysis of the twenty different samples showed different levels of heavy metals concentration. The analysed nine elements are Arsenic, Mercury, Cadmium, Cobalt, Chromium, Nickel, Lead, Vanadium and Zinc. Descriptive statistics was used to explore the heavy metal concentrations individually. Pearson, Kendall tau and Spearman rho correlation coefficients was used to establish the relationships among the elements and the analysis of variance showed that there is a significant difference in the mean distribution of the heavy metals concentration within and between the groups of the 20 samples analysed. The dataset can provide insights into the health implications of the contaminants especially when the mean concentration levels of the heavy metals are compared with recommended regulatory limit concentration

Evaluation of Groundwater Pollution Near Municipal Solid Waste Landfill Site Using ERI Technique: A Case Study in Southwestern Nigeria

Direct current (DC) geoelectrical resistivity measurements have been conducted to investigate groundwater contamination at a non-engineered, open dumpsite facility in Lagos, southwestern Nigeria. The inferred lithologies from the tomographic imaging include topsoil, sandy-clay and sandy units; the delineated low resistive top layer has resistivity values ranging from 0.64-7.5 m typical of leachates and localized within sandy-clay unit extending to depths of 42-52 metres. The groundwaters from the shallow aquifer units are observed to be hazardously contaminated in area where household, market and industrial wastes are known to be disposed improperly. Thus, deeper aquifer units beyond the contaminated layers should be drilled with screened borehole in order to avert immediate groundwater pollution. This study has further demonstrated the efficacy of using surface geophysical techniques to map contaminant plume in dumpsites and determine the extent of groundwater contamination

SEISMICITY ANOMALIES OF M 5.0+ EARTHQUAKES IN CHILE DURING 1964-2015

The study of magnitude-frequency distribution of earthquake hazards in a region remains a crucial analysis in seismology. Its significance has varied from seismicity quantification to earthquake prediction. The analysis of seismicity anomalies of magnitude M => 5.0 earthquakes in Chile from 1964 to 2015 was undertaken by the present study with a view of reporting the trend of earthquake occurrences in the region. Chile has an area of about 756, 950 km2 with an extensive coastline of approximately 6,435 kms. It is situated in a highly seismically and volcanically active zone with a long, narrow strip of land between the Andes Mountains to the east and the Pacific Ocean to the west.It borders Peru to the north, Bolivia to the northeast, Argentina to the east and the Drake Passage in the far south. Of a total of 3,893 earthquakes that have been documented historically, magnitudes Richter 5.0 to 5.9 represent 92.6%, magnitudes 6.0 to 6.9 represent 6.8%, magnitudes 7.0 to 7.9 represent 0.6%, and magnitudes 8.0 to 8.9 about 0.1%. The quantity of earthquakes (a-value) revealed an estimate of 8.4. The b-value was estimated using Gutenberg-Richter (GR) and the Maximum Likelihood Estimation (MLE) methods. The estimated b-value using GR and MLE methods are 0.97 and 1.1 respectively, with an estimated average b-value ≈ 1. The present studies supprort the conclusion that Chile is seismically very active and prone to the recurrence of moderateto-great earthquakes in the future