Fig. 8: Comparison between previous experiments and models of this study.

Red arrows and dashed curves indicate the boundary velocity function. a Riedel-type experiment [e.g., ref. ^1,17,33–39] showing early formation of R-shears coalescing into a Y-shear above the imposed velocity discontinuity. b Riedel-type restraining bend experiment [e.g., refs. ^20,26,27] showing the formation of a sigmoidal push-up structure above an imposed velocity discontinuity. c Distributed shear experiment [e.g., refs. ^31,32] showing the formation of parallel R-shear zones and antithetic R'-shear zones. d Models of this study for α > 15^∘ and Δ > 60 km showing the formation of parallel Y-shear zones with limited interaction. e Models of this study for α < 15^∘ showing the formation of a sigmoidal push-up structure where the main Y-shear zone splits into two P-shear zones around which thrusts accommodate shortening. f Models of this study for α > 15^∘ and Δ < 60 km showing the formation of duplex structures with parallel Y-shear zones interacting by hard-linkage through P-shear zones around which thrusts accommodate shortening.