2D fractal analysis of synfolding fractures in the Khushalgarh area, eastern Kohat plateau, northern Pakistan

Abstract

Outcrop data has been used to investigate the spatial distribution of fracture system that has affected the Miocene Kamlial Formation of the Khushalgarh syncline from foreland area of the Pakistani Himalaya. The fracture system is dominated by near-orthogonal network of NE-SW and NW-SE striking fractures. The NE-SW fractures follow the axis of the syncline, whereas NW-SW fractures crosscut the fold axis. The scaling properties of these fracture system are analyzed from high quality, outcrop scale digital photographs of two locations, A and B. After digitization of fractures on commercially available drawing software, 2D binary images were prepared for standard box-counting technique. The fracture sets are considered as a whole and not as an individual set of fractures. The results show that the spatial distribution of fractures and their growth follow power-law with fractal dimension (D) at location A (D = -1.153±0.057) and B (D = - 1.156±0.050), and have upper and lower fractal limit. The D values are effectively identical with minimum standard errors. The results conclusively suggest that there is a genetic link between the fractures from one location to another and that they developed synchronous with the folding event. The results have important implications on the geometry and growth propagation of the fracture development during folding, where the fracture sets are interpreted as tectonic in origin and are synchronous with the post-Miocene folding of the Kamlial Formation and are not pre- or post-folding fractures.