(a) Mean anomaly at which individual fracture segments first experience opening (σ_xx > 0) in a model with ψ = 0 and F = 0. Polar stereographic projection of region south of 64° S, showing locations of digitized fracture points. Only every third point is shown for clarity (220 points are shown). (b) As for panel (a), but with ψ = 45°. (c) As for panel (a), but with F = 05. (d) As for panel (a), but showing mean anomaly at which individual fracture segments first experience right-lateral shear (σ_xy > 0).