Abstract

Characterization of fracture anisotropy in Aiyegunle area of Igarra Southwestern Nigeria was done by geologic mapping of exposed outcrops and azimuthal resistivity survey (ARS) at three vertical electrical sounding (VES) stations. Rose diagrams, stereographic projections, and resistivity anisotropy polygons were used to delineate and integrate surface and subsurface structural trend. Dominant joints orientation is North-west-South-east (NW-SE) and North- South (N-S). The orientation of fracture in the subsurface is N-S with anisotropy prominent in the NW-SE direction. The coefficients of anisotropy (λ) at depth are less than 2.2, with the degree of fracturing opening and closing with depth. The diversity of fracture attitude implies they were products of different tectonic episodes corroborating evidence of multiphase deformation. The fracture directions suggest that surface structures are hard-linked and produced by similar tectonic event relative to subsurface fractures of Pre-Pan African orogenies.

Key words: Fractures, orientation, surface, subsurface, anisotropy.