Figure 2. Contact area and normal stress and particle velocity measurements indicate slip-pulses in the positive direction and supershear cracks in the negative one.

Comparisons of contact area, A(x,t) (a,d,g), normal stresses, σ_yy(t) (b,e,h), and particle velocities, , (c,f,i) for the ruptures presented in Fig. 1b. Signs of correspond to the motion directions denoted in Fig. 1a. Line colours represent measurements within the different blocks: red lines denote measurements within the stiff material (PMMA) and blue measurements within the compliant material (PC). (a–c) Homogenous interface, x_tip=109 mm: (red dashed line) top block, (solid line) bottom block. Bimaterial interfaces, (d–f) positive direction, x_tip=125 mm and (g–i) negative direction, x_tip=87 mm. Ruptures along the positive direction are characterized by highly localized signals compared with those in the homogenous and negative directions. Insets in c,f and i: measurements for −60<x−x_tip<0 demonstrate slip localization solely in the positive direction. Line colours in d and g correspond to the rupture propagation directions denoted in Fig. 1.