Evidence for universal earthquake rupture initiation behavior

Earthquake onsets provide a unique opportunity to study physical rupture processes because they are more easily observable than later rupture stages. Despite this relative simplicity, the observational basis for rupture onsets is unclear. Numerous reports of evidence for magnitude-dependent rupture onsets (which imply deterministic rupture behavior) stand in contradiction to a large body of physics-based rupture modeling efforts, which are mostly based on inherently nondeterministic principles. Here we make use of the abundance of short-distance recordings available today; a magnitude dependency of onsets should appear most prominently in such recordings. We use a simple method to demonstrate that all ruptures in the studied magnitude range (4<8) share a universal initial rupture behavior and discuss ensuing implications for physical rupture processes and earthquake early warning.