Foreshock-induced slip transients set mainshock nucleation timing

Experimental set-up A biaxial apparatus, CrackDyn, was used to perform the experiments (Fig. 1a ). The apparatus housed two PMMA plates (40 × 10 × 1 cm and 45 × 10 × 1.8 cm). Experiments were conducted on PMMA rather than natural rocks because it provides three main advantages for scaling laboratory observations to natural fault systems. First, owing to its lower elastic stiffness compared with rocks, the state-evolution slip distance, L , and cohesive zone size, X c , are smaller in PMMA. …