Probabilistic seismic hazard analysis of New Zealand

Abstract

We construct probabilistic seismic hazard (PSH) maps for New Zealand that are based on the distribution and long‐term recurrence behaviour of active faults and the spatial distribution of earthquakes observed in historic time. Slip rate, single‐event displacement, and return time data for 154 active faults (including segments of the Hikurangi and Fiordland subduction zones) are combined with observations of the magnitudes and rupture lengths of large New Zealand earthquakes since 1843 and the instrumental record of seismicity since 1964 to predict the future ground motions that will occur across the country. Maps of the peak ground accelerations and 0.5 s response spectral accelerations expected at 10% probability in 50 yr on “rock” show the highest accelerations (>0.2g and locally over 0.6g) in a belt that extends from the southwestern end of the country to the northeastern end, along the faults that accommodate essentially all of the relative plate motion between the Australian and Pacific plates. Accelerations of >0.4g are predicted for Wellington City, which lies within the belt of high PSH, whereas accelerations of <0.2g are predicted for Christchurch, and <0.1g for Auckland and Dunedin Cities, all outside the belt of high PSH. Maps of the peak ground accelerations and 0.5 s spectral accelerations expected at 2% probability in 50 yr show accelerations of 0.7g for Wellington and <0.2g for the other cities. The PSH of Wellington is produced by the predicted occurrence of large‐to‐great earthquakes at distances of <50 km, whereas the PSH of the othercities is generally produced by the predicted occurrence of large earthquakes at distances of 50 km or more. Of all the major urban areas of New Zealand, Wellington is subject to the highest seismic hazard.