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Background: Structures such as faults, joints and fractures of diverse patterns have acted as precursors of several slope instability cases within the Benue Trough Nigeria. In some cases, the structures by their nature weakened and also created avenues that streams took advantage to further destabilize the rock slopes. In other cases, structure orientation played significant roles in the mobility and eventual runout distance of debris flow and avalanches in the region. Detailed field-based structural, fracture and paleostress analyses were therefore carried out to determine the fractural patterns that correlate to reported instability and landslide cases in the region; and to produce models that reveal areas with heightened risk.

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The Upper Benue trough of Nigeria consists of basins and horsts characterized by numerous structural features. Detailed study of one of the basins revealed sets of “centimetric”, riedel type “en-echelon” NE-SW trending strike slip faults contained in a number of brittle and ductile shear zones characterizing the basement/sediment boundary. Structural analysis suggests that the Moku sub-basin has been pulled apart along a releasing bend in between NE – SW strike slip faults and that three principal axes of stress were acting on the sub-basin during its formation. The maximum stress (1) with orientation 34/304 was responsible for the fault overlap (basin length), whereas the minimum stress (σ_3) with orientation 18/201 controlled the fault separation (basin width). These suggest a qualitative model showing the Moku sub-basin as a separate basin, which must have coalesced with adjacent sub-basins. Deposition of Bima sediments in the basin was closely controlled by tectonism. The immature B1 sediments are restricted mostly to the faulted margin of the basin. The more matured B2 and B3 sediments are distributed around the less disturbed areas.