Testing and Evaluation of the New Zealand National Seismic Hazard Model 2022

Abstract

ABSTRACTWe summarize the work that has been done within the New Zealand National Seismic Hazard Model 2022 (NZ NSHM 2022) to evaluate and test the updated hazard model and its components against observational data. We undertake a two-phase analysis to learn about the performance of the hazard model with respect to several limited databases. Phase 1 is the evaluation phase, involving multiple efforts to optimize various source rate model and ground-motion characterization model components against: (1) the New Zealand earthquake catalog for 1950–2020; (2) international catalogs (where relevant); and (3) New Zealand paleoseismic and geodetic data. Phase 2 involves testing the hazard results. We perform ground-motion-based testing of the NZ NSHM 2022 exceedance rates against the observed exceedance rates for strong-motion stations around New Zealand. To account for the modeled variability in rate, the comparisons are done by assuming a binomial distribution about the mean exceedance rate for 0.1g and 0.2g at each station location. We use a combined approach that considers the full epistemic uncertainty distribution for those exceedance rates by weighting the binomial for each branch in the logic tree. We find that, in general, the observed exceedance rates can be drawn from the NZ NSHM 2022 with probabilities greater than 0.05, and that the discrepancies are generally confined to areas close to major earthquake sequences (e.g., Christchurch). These sequences were not considered in the NZ NSHM 2022 forecast. This initial iteration of testing does not provide evidence to reject the NZ NSHM 2022 based on the New Zealand accelerograph record. Importantly, we can only draw limited conclusions from the testing due to the very short time frame of data available for testing.