Diversity and transition of rupture styles governed by rate-and-state friction

SUMMARY The complexity of earthquake rupture dynamics and the diversity of observed seismic behaviours are fundamentally governed by the frictional properties of faults and their response to tectonic stress. Grounded in the rate-and-state constitutive law derived from laboratory experiments on rock friction at slow slip velocities, we employ a fully dynamic model to investigate how frictional conditions give rise to a diverse range of rupture modes and influence their propagation dynamics. Under uniform background stress and nucleation conditions, the rupture type, whether supershear, sub–Rayleigh, self–arresting or slow self–arresting rupture (SSAR), is governed by the relative contributions of the direct effect and the evolution effect, expressed as $R = 1 - \frac{a}{b}$, together with the normalized characteristic slip distance D. Their respective regimes are summarized in a phase diagram. We demonstrate that the friction parameters R and D significantly influence the rupture process, with R primarily enhancing stress release and slip during rupture, while D predominantly controls the rupture speed. For varying values of R, there exists an optimal intermediate D that maximizes rupture velocity. Furthermore, simulations suggest that when frictional parameters approach the boundaries between different rupture types regimes, the earthquake may not be confined to a single mode. Instead, a single rupture event can exhibit complex, continuous, yet rapid transitions between distinct types under a single triggering without interruption. These transitions can occur smoothly among various rupture types, including transitions from SSAR to sub-Rayleigh rupture and subsequently to supershear rupture. This study indicates the key role of frictional properties in governing rupture dynamics, offering new perspectives on the inherent complexity of earthquake processes.