Application of paleostress analysis for the identification of potential instability precursors within the Benue Trough Nigeria

Abstract

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. Three fracture sets were isolated from analysis of fracture orientations and field relationships: Pre-folding (JT), Syn-Folding (JS) and Post Folding (JC) fracture systems. Paleostress analysis carried out on these fracture systems using the TENSOR™ software tool yielded three paleostress tensors corresponding to transtensional stress tensor with ENE-WSW direction of maximum extension (SHMIN), oblique compressive (transpressional) tensor with NW-SE direction of maximum shortening (SHMAX), and transtensional tensor with WNW-ESE direction of maximum extension (SHMIN). These tensors are related to the prevailing plate tectonic stress regimes affecting the entire Benue trough and the West and Central African Rift System (WCARS). Our pre- and post-tectonic models have revealed the reasons for instability and the likely places where future failures may be located. This is the first such analyses in the region and it is hoped that the results can broaden the use and applicability of paleostresses in failure-prone terrains for future risk and disaster reduction/assessment within the Trough and in other areas prone to structure-controlled landslides disaster.