3:00 PM - 3:15 PM
[SCG49-06] Characteristics of segmented and multi-fault earthquake-rupture models in New Zealand
Keywords:multi-fault ruptures, segmented faults, seismic hazard
Multi-fault ruptures are common globally in historical earthquakes, and here we consider their impact on New Zealand seismic hazard. We compare ground-shaking hazard forecasts from the 2022 New Zealand National Seismic Hazard Model (NZ NSHM 2022), which incorporates many multi-fault ruptures (‘Multi-fault Model’), with hazard from a simpler model of characteristic earthquakes on individual faults or fault segments (‘Segmented Model’). The ‘Multi-fault Model’ includes very low-probability rupture lengths of up to ∼1100 km and a mean length of ~230 km, whereas the ‘Segmented Model’ has a maximum rupture length of 414 km with most lengths <200 km (mean, ~47 km). Due to these differences in lengths a greater proportion of the seismic moment budget is accommodated by smaller (e.g., <Mw 7.5) earthquakes in the ‘Segmented Model’ compared to the ‘Multi-fault Model’. Therefore, the annual rates of Mw 6.9–7.5 earthquakes are more than an order of magnitude higher for the ‘Segmented Model’ compared to the ‘Multi-fault Model’ (0.132–0.24/yr vs 0.027/yr). Surprisingly, despite these dramatic differences in rupture lengths and rates, the calculated ground-shaking hazard at 10% probability of exceedance (PoE) in 50yr is within a factor of two at 95% of sites. In most areas, seismic hazard at 10% PoE in 50 yr is greater for the ‘Segmented Model’ than the ‘Multi-fault Model’, with notable exceptions along the central Alpine fault and the Taupō Rift in the central North Island. These results may change when longer time periods (e.g., 2% PoE in 50 yrs) and multi-fault ruptures including both the subduction interface and upper-plate faults are considered. Work on these topics is ongoing and will be discussed during this presentation.