Slip initiation along natural faults is mediated through propagating rupture fronts. What mechanisms drive these ruptures, how fast they propagate, and what makes them stop are central questions of earthquakes source mechanics. Xu et al. (2019, https://doi.org/10.1029/2018JB016797) and Kammer and McLaskey (2019, https://doi.org/10.1016/j.epsl.2019.01.031) study rapid rupture propagation in large-scale rock experiments. Their detailed high-speed strain measurements reveal that rupture fronts are analogous to shear cracks, driven by singular fields at their tip. By comparing these measurements with simulations and analytical fracture mechanics solutions, the authors provide estimates of the fracture energy and frictional properties that regularize these singularities. Building on that, the fracture mechanics framework has been successfully employed to describe rupture arrest and propagation.