Warwick Smith

National Seismic Hazard Model for New Zealand: 2010 Update

A team of earthquake geologists, seismologists, and engineering seis- mologists has collectively produced an update of the national probabilistic seismic hazard (PSH) model for New Zealand (National Seismic Hazard Model, or NSHM). The new NSHM supersedes the earlier NSHM published in 2002 and used as the hazard basis for the New Zealand Loadings Standard and numerous other end-user applica- tions. The new NSHM incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new New Zealand-based and international scaling relationships for the parameterization of the faults. The dis- tributed seismicity model has also been updated to include post-1997 seismicity data, a new seismicity regionalization, and improved methodology for calculation of the seismicity parameters. Probabilistic seismic hazard maps produced from the new NSHM show a similar pattern of hazard to the earlier model at the national scale, but there are some significant reductions and increases in hazard at the regional scale. The national-scale differences between the new and earlier NSHM appear less than those seen between much earlier national models, indicating that some degree of consis- tency has been achieved in the national-scale pattern of hazard estimates, at least for return periods of 475 years and greater. Online Material: Table of fault source parameters for the 2010 national seismic- hazard model.

Computer file of New Zealand earthquakes

Abstract The Seismological Observatory, Wellington, is often asked to supply lists of earthquakes, chosen because they have occurred in particular geographical areas of New Zealand, near certain towns or planned construction sites, or on other criteria. In the past the preparation of such a list has necessitated a time-consuming examination of the printed Seismological Observatory Bulletins and other less accessible records. This procedure has now been greatly simplified by the preparation of a master file of earthquakes known to have occurred in the New Zealand region. This file contains over 14000 earthquake origins and is stored on magnetic tape for use on the Burroughs B6700 computer at the Victoria University of Wellington.

Volcanic ashfall in New Zealand – probabilistic hazard modelling for multiple sources

Abstract The airfall ash component of the New Zealand Probabilistic Volcanic Hazard Model (PVHM) estimates the likelihood of volcanic ash deposits of any given thickness at any site, based on the frequency-magnitude relations of all the significant volcanic sources in New Zealand and the wind distribution statistics. The main source of error in these models is the uncertainty in the historic ash production records of the volcanoes. Another source of error is that the current wind pattern may not be the same as during the period that the observed ash record was deposited. The spatial distribution and magnitude/frequency curves of volcanoes are very different from those of earthquakes, and this is reflected in the hazard models. Whereas a typical probabilistic earthquake hazard model will have the expected acceleration increase by a factor of 3 to 5 between 500 and 10,000 year return periods, the expected ash thickness can change by up to a factor of 1000 over these periods. The Auckland Volcanic Field is now occupied by New Zealands largest city, so the comparatively small and infrequent eruptions potentially represent a major social and financial hazard. Our modelling of lake core ash records in the Auckland area suggests that the known vents and eruptions probably represent less than half of the total volcanic activity from the field, and that the hazard from local events is comparable to that from more distant sources. An area needing improvement is the hazard in Auckland from local eruptions, with more ash thickness data and better basaltic eruption models.

Probabilistic Modeling of Post-Earthquake Fire in Wellington, New Zealand

Wellington, the capital of New Zealand, has both high seismic and high post-earthquake fire risk because it straddles the highly active Wellington Fault, has many closely spaced wooden buildings, and has a fragile water supply system. Repeated modeling of a Wellington Fault earthquake showed that the distribution of fire losses was much broader than that of the shaking losses, so that while fire losses were usually much smaller than the preceding shaking losses, they could occasionally be much greater than the shaking losses. Probabilistic modeling using a synthetic catalog of earthquakes gave estimates of post-earthquake fire losses in Wellington that were relatively minor for return periods up to 1,000 years, equal to the shaking losses at about a 1,400-year level, and that dominated the losses for 2,000-year and longer return periods.

On Assessment and Disaggregation of Seismic Risk

Abstract Seismic risk presented in terms of the annualized loss is useful to the insurance industry, but it is a very limited contribution to the needs of other risk managers. Other measures can be evaluated readily, such as discretization of the loss curve into short-term, medium-term, and long-term losses, and disaggregation to identify the predominant earthquake sources. These measures are not limited to single site assessments, but all can be evaluated for geographically distributed portfolios, and they are useful to risk managers who are seeking to mitigate against possible losses.