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Abstract

Recent multifault ruptures, such as the 2010 El Mayor-Cucapah and 2016 Kaikōura earthquakes, have demonstrated the potentially complex interactions of faults in single earthquakes, contrasting with the typical assumption of characteristic fault ruptures in seismic hazard assessment. Physics-based earthquake simulators, such as RSQsim (Dieterich & Richards-Dinger, 2010; Richards-Dinger & Dieterich, 2012), offer one approach to understanding potential multifault earthquakes, and their effects on the time-dependence of earthquake recurrence. Here we investigate the effects of known uncertainties in fault-network geometry on the outputs of such simulators. We use the Canterbury and North Marlborough regions of the South Island of Aotearoa New Zealand – the epicentral region of the 2016 Kaikōura earthquake – as a case study. Using recently developed fault modelling tools, we create 3D fault networks corresponding to a range of possible fault-network geometries in the region, including the potential for missing faults and variable geometries at fault intersections. The different networks we develop are motivated by key observations from the Kaikōura earthquake, such as the high proportion of previously unmapped faults in the rupture (Litchfield et al., 2018), and by explicit uncertainties in the New Zealand Community Fault Model (Seebeck et al., 2022). We generate synthetic earthquake catalogues on these different fault networks and investigate their similarities and differences, both statistically and in terms of the generated multifault ruptures. By doing so, we are able to better understand how the “known unknowns” of fault-network geometry impact earthquake simulator outputs.