Consideration and propagation of epistemic uncertainties in New Zealand probabilistic seismic hazard analysis

Executive Summary

This report presents the results from the consideration of epistemic uncertainties in New Zealand probabilistic seismic hazard analysis. The methodology accounts for uncertainties in the earthquake rupture forecast due to uncertainties in fault geometry, slip parameters, and magnitude scaling relationships; as well as uncertainty in the predicted distribution of ground motion by utilizing multiple ground motion prediction equations. The hierarchy of ground motion prediction equations was developed based on examination of the bias in various NZ-specific and foreign models using a dataset of observed ground motions in New Zealand. Due to the present lack of fault-specific data quantifying uncertainties for the majority of faults in NZ, representative values based on judgement and a limited number of NZ and foreign fault-specific data available were utilized for such faults. Probabilistic seismic hazard analyses are conducted for two vibration periods of spectral acceleration (PGA and SA(2.0)) for site class B (rock) and D (soft/deep soil) conditions in Wellington and Christchurch. The results illustrate that variation in seismic hazard due to various ground motion prediction model represent the largest source of uncertainty considered. Of the earthquake rupture forecast uncertainties considered, the magnitude-geometry scaling relationships was the most significant, followed by rupture length. Recommendations for prioritization of seismic hazard research are discussed in light of the observed results.