Figure 4
From: Velocity-strengthening friction significantly affects interfacial dynamics, strength and dissipation
Propagation of rupture fronts in the first event for (a) All three models and (b) the LS and STL models.
xtip is the spatial location of the front tip, cf. Fig. 5. tc is the time where the front starts to propagate, cf. Fig. 3. Note also the vast difference in timescales between the panels. The wave speed in this system is 
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