Fractal analysis of anisotropic shear-fracture roughness from rocks and analogue laboratory models: A new approach for heterogeneous-slip characterization

Abstract

Shear fracture surfaces are commonly rough on varied scales, and understanding the roughness properties is crucial to predict their slip behaviour. Using natural rock samples from the Singhbhum Shear Zone, eastern India, this study develops an approach to heterogeneous surface roughness analysis of shear fractures, forming two distinct domains: striated, anisotropic zone and non-striated, isotropic zone. Analogue experiments run on brittle-ductile models under a pure shear condition produce similar heterogeneous roughness characteristics of shear fractures. Using a laser profilometer, we constructed 3D topologies of both natural and experimental shear surfaces, which are presented to show the distinctive roughness characteristics of the striated and non-striated zones in terms of their fractal properties. ΔD, which stands for the difference between across- (D⊥) and along- (D∥) the slip direction, is calculated to evaluate the degree of their roughness anisotropy. This fractal parameter indicates strong anisotropy with ΔD = 0.0787–0.2118 in striated zones, which is significantly weak, where ΔD = 0.0024–0.0603 in non-striated zones. Finally, the article presents an in-depth discussion of this roughness study from the perspective of slip-stuck kinematics on shear surfaces from laboratory experiments and their geophysical implications, e.g., interpretation of earthquake event patterns on seismic faults and permeability of fractured rocks.