Probabilistic seismic hazard analysis of New Zealand

We construct probabilistic seismic hazard (PSH) maps for New Zealand that a re based on the distribution and long-term recurrence behaviour of active f aults 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 l arge New Zealand earthquakes since 1843 and the instrumental record of seis micity since 1964 to predict the future ground motions that will occur acro ss the country. Maps of the peak ground accelerations and 0.5 s response sp ectral accelerations expected at 10% probability in 50 yr on "rock" show th e highest accelerations (greater than or equal to 0.2g and locally over 0.6 g) in a belt that extends from the southwestern end of the country to the n ortheastern end, along the faults that accommodate essentially all of the r elative plate motion between the Australian and Pacific plates. Acceleratio ns of >0.4g are predicted for Wellington City, which lies within the belt o f 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 ex pected 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 p redicted occurrence of large-to-great earthquakes at distances of <50 km, w hereas the PSH of the other cities is generally produced by the predicted o ccurrence of large earthquakes at distances of 50 km or more. Of all the ma jor urban areas of New Zealand, Wellington is subject to the highest seismi c hazard.