Modelling asymmetric deformation along a curved strike-slip basement-fault system

Abstract

Large-scale curved strike-slip fault systems along which significant amounts of displacement have taken place are common in nature. Scaled analogue experiments were used in this study to investigate strike-slip deformation in cover units above a curved basement-fault system simulated by a rigid plate with an in-built curvature depicting a half-circular fault. The model results show that en-echelon, right-stepping Riedel shears and low-angle synthetic shears (Y-shears) always form at the beginning of deformation, and grow outwards with splay faults, most of which evolve into thrusts at later stages of deformation. Digital image correlation (DIC) analyses of the surface displacement vectors show that a diffuse zone of deformation progressively changes into en-echelon shears, which gradually develop into throughgoing shear zones with further deformation. The geometries of Riedel shears along two sides of the basement fault (i.e. concave and convex sides) show significant differences in fault shape and intersection angles between the faults and the curved basement fault, indicating an asymmetry in deformation with a much wider deformation zone occurring on the concave side. As a result, en-echelon and/or overlapping flower structures develop along the curved basement strike-slip fault system. In particular, Riedel shears with a upward-convex geometry are localised in both sides of the curved basement fault and a continuous reverse oblique-slip fault forms at the concave side. When compared with the geometry of curved strike-slip faults in nature (e.g. the Daliangshan shear zone in Xichang basin and the Red River shear zone in the Yinggehai basin, China) the model results depict the asymmetric evolution pattern of the faults on either side of curved basement faults.