The motion- and scale-dependence of rupture prestress and criticality: implications for complexity of earthquake sequences and laboratory vs field inferences of fault strength

Valere R. Lambert, & Nadia Lapusta

Submitted August 26, 2020, SCEC Contribution #10782

Determining critical stress conditions on faults is a key goal of fault mechanics highly relevant to seismic hazard. Using numerical simulations of earthquake sequences on rate-and-state faults with enhanced dynamic weakening due to thermal pressurization of pore fluids, we demonstrate that the average shear stress that a fault can sustain before rupture - a measure of fault strength - decreases as the total rupture size increases, becoming much smaller than the local shear stress required for nucleation. This effect is due to significant coupling between propagating fault slip, the resulting dynamic stress transfer, and evolving local shear resistance. Fault models with more efficient weakening result in larger decrease of shear prestress with the rupture size and exhibit decreasing complexity of earthquake sequences. The findings highlight the importance of finite-fault effects and reconcile the inferred apparent weakness of mature faults with laboratory measurements of shear resistance.

Citation
Lambert, V. R., & Lapusta, N. (2020). The motion- and scale-dependence of rupture prestress and criticality: implications for complexity of earthquake sequences and laboratory vs field inferences of fault strength. Earth and Planetary Science Letters, (submitted).