Probabilistic seismic hazard assessment of New Zealand

Technical Abstract

New Active fault data, seismicity data, attenuation relationships & methods

We present the results of a new probabilistic seismic hazard analysis (PSHA) for New Zealand. The PSHA incorporates geological data describing the location and earthquake recurrence behaviour of 305 active faults, a seismicity catalogue with greatly improved locations for many events, new attenuation relationships for peak ground acceleration and spectral acceleration developed specifically for New Zealand, and state-of-the-art PSH methodology developed in New Zealand and the USA. The methodology and data used in the PSHA builds on the data and methods used in an experimental PSHA of New Zealand by Stirling et al. (1998), and supersedes the PSHAs of Matuschka et al. (1985) and Smith and Berryman (1983, 1986), which were largely based on the historical record of earthquakes (historical recording began with European settlement in 1840). These models served as the basis for the current New Zealand Loadings Standard NZS4203:1992 (Standards New Zealand, 1992). PSH maps produced from our new model show the highest hazard to occur in Fiordland (vicinity of the Fiordland subduction zone and the offshore extent of the Alpine Fault), along the axial tectonic belt (Westland, Marlborough, north Canterbury, Wellington, Wairarapa, western Hawke's Bay and eastern Bay of Plenty), the Taupo Volcanic Zone (TVZ, a zone of crustal extension and volcanism running from the central North Island volcanoes to the Bay of Plenty), and in the seismically active area of north Westland/southwest Nelson (area of the Buller and Inangahua earthquakes). The maps show generally similar patterns of hazard to the maps of Stirling et al. (1998), but very different patterns to those shown on the maps of Smith and Berryman (1983, 1986) and Matuschka et al. (1985). The largest differences exist in the vicinity of the major active faults, which generally have not produced large earthquakes in historic time, but have produced them abundantly in prehistoric time.

Examination of the PSHA at the major population centres reveals that they have the following rank in decreasing order of hazard; Wellington, Christchurch, Dunedin and Auckland. The hazard is highest in Wellington, since it is close to a number of major active faults, and within an area of high seismicity in historical time. In comparison, the other centres are generally located in areas away from the major active faults, and in areas of relatively low seismicity rates.