Seismic hazard with deterministic maximum limits: Considerations in a New Zealand-specific context

This paper outlines the consideration of deterministic limits on maximum ground motion levels within seismic design codes and standards. The specific motivation is to outline the basis for the exclusion of such a limit in the 2024 draft Technical Specification for NZS1170.5 [1], despite the presence of such limits in NZS1170.5:2004 [2]. An overview of the historical consideration of so-called ‘deterministic’ and probabilistic seismic hazard analysis methods is provided, as well as how they have translated into contemporary seismic design codes and standards in New Zealand (NZ) and internationally. The fundamental issues with deterministic maximum limits are outlined through the use of examples in a NZ-specific context. The underlying reason ‘well above average’ ground-motion intensity levels (for a given earthquake scenario) are prevalent in regions of high seismicity is discussed, as well as other common misconceptions that lead to the use of deterministic limits to achieve apparently realistic design ground motion intensities. Finally, in the vein of the hazard-risk separation principle, sentiments are expressed for achieving economic and resilient seismic design in regions of high seismicity without resorting to implementing deterministic limits.