New Zealand National Seismic Hazard Model Revision 2022: Hazard changes with respect to NZ NSHM 2010

Abstract

Revision of New Zealand National Seismic Hazard Model (NZ NSHM 2022) represents a significant change not only in hazard results but also in terms of methods and processes in comparison to NZ NSHM 2010. The changes span over the entire model components such as seismicity rate model (SRM), ground-motion characterization model (GMCM) including modelling of site-effects. One important change is the quantification of the plausible range of epistemic uncertainty in hazard estimates. This is achieved by using multiple (alternate) models within the full SRM and GMCM logic trees. In this study, we present a systematic comparison of hazard results from NZ NSHM 2022 against those from NZ NSHM 2010. Specifically, it demonstrates the impact of changes in GMCM and SRM individually. Additionally, the comparisons are illustrated in terms of hazard sensitivities with regard to a few modelling and parameter choices in GMCM and SRM. Our results show that on average the hazard increases by a factor of 1.5-2.0 depending upon the vibration period and location across the country. In high hazard regions such as the eastern part of the North Island the change in GMCM dominates the change in hazard while in low hazard regions (the north-western part of North Island and the south-eastern part of the South Island) the change in SRM is the dominating change. These changes are further dissected in terms of changes originating from different source types (or tectonic types) both in ground-motion characterization and seismicity rate models.