Dynamic Rupture Simulation Reproduces Spontaneous Multifault Rupture and Arrest During the 2016 Mw 7.9 Kaikoura Earthquake

The 2016 Kaikoura (New Zealand) earthquake is characterized as one of the most complex multifault rupture events ever observed. We perform dynamic rupture simulations to evaluate to what extent relatively simple forward models accounting for realistic fault geometry can explain the characteristics of coseismic observations. Without fine parameter tuning, our model reproduces many observed features including the multifault rupture, overall slip distribution, and the locations of the maximum slip and rupture arrest. In particular, our model shows spontaneous arrest of dynamic rupture at the both ends of the ruptured fault system due to smaller prestress levels expected from a regional tectonic stress field. Both the simulated and the observationally inferred source time functions show similar double peaks with a larger second peak. The results illuminate the importance of the 3-D fault geometry in understanding the dynamics of complex multifault rupture. Plain Language Summary The 2016 Kaikoura earthquake in the northern South Island of New Zealand was one of the most complex faulting events ever observed. Previous studies identified surface ruptures along at least a dozen major faults extending over 150 km. Here we use computer simulations to investigate how the complex three-dimensional geometry of faults plays a role in the rupture propagation and termination during the Kaikoura earthquake. We find that our model can explain a number of observations associated with the earthquake. In particular, the model suggests that the termination of propagating rupture at the ends of faults was caused by the unfavorable orientations of these faults with respect to regional tectonic stresses. The results illuminate the importance of three-dimensional fault geometry in understanding the dynamics of multifault earthquakes.