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Characterization of Near Surface Fractures for Hydrogeological Studies using Azimuthal Resistivity Method
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Near Surface Geoscience 2012 – 18th European Meeting of Environmental and Engineering Geophysics, Sep 2012, cp-306-00121
- ISBN: 978-90-73834-34-7
Abstract
Two faults occurring at the Enugu Shale exposure near the Onitsha Fly-over gave the impression of conjugate or antithetic fault pattern with the maximum principal stress during the formation aligning west-north-west. Studied joints also gave a northwest - southeast orientation of the maximum principal stress. Two Azimuthal Resistivity Survey (ARS1 and ARS2) further characterized fractures and confirmed the information furnished by outcrop fracture survey. Graphical interpretation of the ARS data indicates that the dominant fracture strike is oriented in the north-north-west direction at the shallow depths of 7.1, 10.0, 20.0 and 28.3 m. The coefficient of anisotropy, λ ranges from 1.00 to 1.12. The fracture porosity estimated from the azimuthal resistivity survey at the two stations ranged between 0.001 and 0.06. Fractures at localities with relatively high values of λ posses relatively high fracture porosity and relatively low specific surface area and thus more likely to be intensely fractured and permeable. The general orientation of the fractures correlated well with the kinematics of outcrop fracture survey studies in the Enugu area. Extrapolation of the results of this analysis will further enhance the success rate of groundwater exploration and exploitation in the