Diverse slip behaviour of velocity-weakening fault barriers

Seismic barriers are fault portions that promote earthquake rupture arrest and fault segmentation. Despite their fundamental role in controlling the maximum magnitude of earthquakes, the nature of seismic barriers is still uncertain. A common interpretation of barriers as having velocity-strengthening friction—steady-state friction that increases with increasing slip velocity—is only partially consistent with the thermal control of friction observed in laboratory experiments, which implies that most relevant materials in subduction channels are velocity-weakening at seismogenic depths. Here we examine the possibility of velocity-weakening barriers by conducting earthquake cycle simulations along a velocity-weakening megathrust segmented by lateral variations of frictional properties and normal stress. We show that velocity-weakening fault segments display a wide range of behaviours, including permanent barrier behaviour. They can be locked during long periods and release their slip deficit either seismically or aseismically. We quantify the efficiency of velocity-weakening barriers in arresting ruptures using a non-dimensional parameter based on fracture mechanics theory that can be constrained by observations on natural faults. Our results provide a theoretical framework that could improve physics-based seismic hazard assessment. Velocity-weakening seismic barriers in subduction zones display a range of behaviours consistent with geologic structural control on earthquake seismicity, according to earthquake cycle simulations along a megathrust.