Earthquakes big and small: same physics, different boundary conditions

Abstract Self-similarity indicates that large and small earthquakes share the same physics, where all variables scale with rupture length L. Here I show that rupture tip acceleration during the start of dynamic rupture (break-out phase) is also self-similar, scaling with Lc in space and Lc/Clim in time (where Lc is the breakout patch length and Clim the limiting rupture velocity in the subsonic regime). Rupture acceleration in the breakout phase is slower for larger initial breakout patches Lc. Because small faults cannot host large breakout patches, a large and slower initial breakout may be indicative of a potentially large final earthquake magnitude. Initial moment rate ˙Mo also grows slower for larger Lc, therefore it may reflect fault dimensions and carry a probabilistic forecast of magnitude as suggested in some Early Warning studies. This result does not violate causality and is fully compatible with the shared fundamental, self-similar physics across all the magnitude spectrum.