Frequency-Domain Electromagnetic and VLF Data with An Application to Modeling of Basement Structures: A Case Study Within, Ibadan Area, Southwestern Nigeria.

*Abdulbariu Ibrahim1, Baba Aminu Mu’awiya1, Achonwa Kingsley Okechukwu2
1Department of Geology, Federal University Lokoja, Kogi State, Nigeria.
2Department of Chemical/petrochemical engineering, Rivers State University, Port Harcourt

DOI: https://doi.org/10.51584/IJRIAS.2023.8616

Received: 11 May 2023; Revised: 08 June 2023; Accepted: 13 June 2023; Published: 13 July 2023

Abstract: The study area, the church camp is within Ibadan which fall within southwestern basement complex of Nigeria and it is mainly by migmatite-gneiss. The hard rocks are usually characterized by basement fracture which may serve as a conduit for groundwater passage. This has necessitated detail geological and geophysical investigation to accurately and precisely delineate this structure. Geological mapping alongside very low frequency Electromagnetic (VLF-EM) techniques were adopted in which conductivity data were acquired along Fifteen (15) VLF profiles using ABEM WADI. Thirteen (13) of these profiles were in the East-West (E-W) direction which is the dip direction of the structural elements, while the remaining two profiles were in North-South (N-S) direction. The data obtained from the field were processed, filtered and presented inform of profiles and Karous-Hjelt (K-H) filtered pseudo-section to visualise conductivity in (2-D). Pockets of conductive structures were delineated and were interpreted as fractures of various dimension and orientation. Some are single fracture and others are closely-spaced double fractures which some of them joined or fused together at depth with some suspected to contain water while some are dry base on their conductivity/resistivity signature exhibited. In conclusion, VLF-EM has proven to possess the capability to characterize and model the basement fractures and define their dimension, axial orientation and indicates their parallelism which also signifies their origin as regard stress regime that produces the fracture.

Keywords: Migmatite-gneiss, VLF-EM, fracture, Karous-Hjelt pseudo-section, Conductivity.

I. Introduction

The basement complex of Nigeria covers almost fifty percent of the entire land mass of the country. They are hard rocks characterized by low porosity and relatively impermeable but in some cases they fractured due to tectonic episode. It is in this fractures that groundwater occurs. A typical Basement Complex terrain distinguished by the presence of hills and mountains thereby making access to potable water is challenging. Changde et al (2022) and Andarawus et al (2022) asserted that due to the complexities associated with Basement Complex terrains, proper understanding of the hydrogeological characteristics of the auriferous units is imperative for sustainable exploitation and development of groundwater resources. Groundwater exploitation in basement-complicated terrain necessitates a thorough grasp of its hydrological properties. Groundwater is mostly trapped in permeable and leaky weathered areas in the Basement Complex terrain.

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