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Two-Dimensional Empirical Rupture Simulation: Examples and Applications to Seismic Hazard for the Kaikōura Region, New Zealand


 Multifault earthquakes present a significant challenge to seismic hazard assessment. Historical surface rupturing earthquakes provide empirical constraints on the physical variables that control rupture length and the occurrence of multifault earthquakes. Here, we develop a rupture simulation that uses relationships derived from surface rupture databases to characterize different rupture pathways initiating on a seed fault. This empirical rupture simulator uses step distance, number of steps, angular change, and kinematic change variables to compute a combined co-rupture probability for all fault section connections within 10 km of the seed fault and subsequent active ends of the propagating rupture. Ruptures end when all possible active ends fail to pass to the next section and the next iteration begins. We applied our model to two seed faults in the region of the 2016 Kaikōura (New Zealand) earthquake and compared the results to independent constraints on paleoseismic magnitude, rupture segmentation, and global estimates of rupture complexity. Rupture set characteristics change dramatically based on seed fault location and indicate some support for geologically defined rupture segmentation. Length-based magnitudes generally agree with those estimated from paleoseismic single-event displacements. Our preferred model reproduces total trace complexity of historical earthquake catalogs and rarely generates events involving faults that ruptured in the Kaikōura earthquake. This approach may be useful for filtering or weighting scenarios in earthquake rupture forecasts. Alternatively, it could be used as a straightforward tool for directly estimating maximum likely magnitudes. Further developments incorporating slip rate-based seeding might allow results to be compared with other established methods of rupture simulation.