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BP Exploration, Farburn Industrial Estate, Dyce, Aberdeen AB21 7PB UK (e-mail: stephan.bergbauer{at}bp.com)
The curvature of geological surfaces has been used to predict areas of elevated strain, deformation and fracture density. The research presented here tests if and to what extent a geometric measure such as normal surface curvature can be used as a proxy for deformation by comparing field observations with geometric modelling results. This is achieved by first quantifying fracturing in outcrop and then by performing a curvature analysis of the deformed bedding surface. This research suggests that curvature analysis by itself does not allow for the prediction of deformation: fracture density in the Emigrant Gap anticline is unrelated to horizon curvature, and synfolding fractures are aligned with prefolding fractures instead of the directions of principal curvature.
Normal surface curvature by itself has only limited value in predicting strain or fracture density; however, surface curvature is a unique descriptor of shape. Describing the geometry of a horizon quantitatively is an essential first step when attempting to compare physical and numerical models with natural surfaces. The tools presented here allow for unique descriptions of three dimensional folded surfaces that are based on the normal surface curvature, and they provide the necessary mathematical rigour and flexibility to allow for descriptions of non-cylindrical folded surfaces.
