Uddalak Biswas , Manaska Mukhopadhyay, Nibir Mandal

Combining field observations with analogue laboratory experiments, this study aims to use surface-roughness characteristics as an indicator of the heterogeneous slip partitioning along shear surfaces. We investigated the roughness of shear surfaces in sheared quartzite of the Singhbhum Shear Zone, eastern India, and identified two distinct kinematic domains: slip zone and stuck zone, marked by strong and weak or no roughness anisotropy, respectively. The experiments, run on brittle-ductile models under a pure shear condition suggest the initial inclination (θ) of shear fractures to the compression direction as a crucial factor in determining their competitive development (measured in terms of their relative area coverage) on the shear surface. Using a laser profilometer we constructed 3D topologies of both field and experimental shear surfaces, which are presented to show their distinctive roughness characteristics. The slip and stuck zones differ from each other in the fractal properties of their surface irregularities. ΔD [difference between across- (D⊥) and along- (D∥) slip direction] is calculated to evaluate the degree of roughness anisotropy. This fractal parameter indicates strong anisotropy in slip (ΔD = 0.0787 – 0.2118) zones, which is virtually absent in stuck zones (ΔD = 0.0024 – 0.0603). We thus propose ΔD as an effective parameter to delineate the slip and stuck zones on a shear surface. Finally, the article presents an in-depth discussion of the geological implications, e.g., earthquake event patterns of this slip-stuck roughness study.