Fig. 1. Experimentally measured supershear rupture velocities.

(A) Two PMMA blocks are used in a stick-slip friction experiment. We consider the elastic medium to be 2D with a quasi 1D frictional interface and measured the full 2D tensorial strains along and ≈3.5 mm above the frictional interface (blue squares). (B) Real contact area A(x, t) measurements along the interface, normalized before the event, show rupture nucleation at x ≈ 0, acceleration, and transition to supershear at x ≈ 50 mm. (C) Shear stress variations, τ = σ_xy – ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}^{\mathrm{r}}$, relative to the rupture tip arrival time, t_tip, measured at x = 105 mm. Arrows denote the dynamic stress drop τ₀ and peak shear strength τ_p. We obtain τ_p from the measured cohesive zone size. The gray curve schematically depicts the interfacial shear stress evolution. (D) Measured rupture velocities for two examples of rupture events in experiments with a dry interface. (B), (C), and the blue example in (D) correspond to the same rupture event.