A large earthquake unlocks a fault-zone via dynamic rupture while releasing part of the elastic energy stored during the interseismic stage. As earthquakes occur at depth, the analyses of earthquake physics rely primarily on experimental observations and conceptual models. A common view is that the earthquake instability is necessarily related to the frictional weakening that is commonly observed in shear experiments under seismic slip velocities. However, recent experiments with frictional interfaces in brittle acrylics and rocks have explicitly demonstrated that no characteristic frictional strength exists; a wide range of stresses (‘overstresses’) are sustained prior to rupture nucleation. Moreover, the experimentally observed singular stress-fields and rupture dynamics are precisely those predicted by fracture mechanics. We therefore argue here that earthquake dynamics are best understood in terms of dynamic fracture mechanics: rupture dynamics are driven by overstresses, but not directly related to the fault frictional properties.