- Title
- Review of tsunami hazard in New Zealand
- License
- Public Domain (PD)
-
+ Works in the public domain may be used freely without the permission of the former copyright owner.
+ For more info see http://www.copyright.gov/help/faq/faq-definitions.html. - Abstract
- "In this report we have examined all likely sources of tsunami that could affect New Zealand, and evaluated their potential to generate tsunami, the likely waves produced, and the likely size of tsunami at the New Zealand coast. This review builds on the 2005 Review of Tsunami Hazard and Risk in New Zealand, and summarises the current state of knowledge, highlighting the results of new research and changes in scientific understanding between 2005 and 2013. A substantially revised probabilistic hazard model has been constructed for this report, which for the first time estimates the tsunami hazard for all parts of the New Zealand coastline. This report focuses on quantifying tsunami hazard, i.e., the likely size of tsunami for specified timescales, along with estimates of uncertainty. It does not provide estimates of risk, i.e., expected costs of damage and numbers of casualties. Every effort has been made to assign realistic parameters for seismic tsunami sources in terms of their likely earthquake magnitudes and frequencies, but there are large uncertainties. Our probabilistic method incorporates these uncertainties throughout the analysis, so that the results contain realistic ‘error bars’. The hazard posed by tsunami generated by landslides and volcanic activity has been carefully considered. At this time it has not been possible to quantify the hazard from these sources, though research work towards this goal is being undertaken. For most parts of New Zealand, the hazard posed from these tsunami sources on time frames of up to 2500 years is considered secondary to the hazard from earthquake-generated tsunami. This is consistent with the global experience of tsunami, in which relatively few events in the instrumental era have been attributed to landslide and volcanic sources relative to the number of earthquake-generated tsunami. The 2011 Tohoku tsunami in Japan illustrates some of the key changes in scientific knowledge since 2005. That event was the latest in a sequence, starting with the 2004 Indian Ocean tsunami and the subsequent 2009 South Pacific tsunami, that were produced by earthquakes substantially larger than had been considered likely to occur at those locations. These earthquakes contradicted previous geophysical assumptions about the maximum magnitudes of earthquakes that could be created on tectonic plate boundaries. There are now far fewer restrictions on possible maximum magnitudes than was previously thought to be the case, and the new probabilistic model attempts to account for this. It is now known that there was a similar tsunami in Japan in AD 869, indicating that the interval between the largest earthquakes there is over a thousand years. The tectonic plates in Japan are converging twice as fast as those around New Zealand, which suggests that the interval between the largest earthquakes on our local plate interfaces could be in excess of two thousand years. The important implication here is that our brief historical record of 200 years can, on its own, provide very little guidance in estimating the magnitude of the largest earthquakes that New Zealand may experience. To improve estimates of the earthquake potential of subduction plate interfaces around New Zealand, where one plate is pushed below another, we must study the evidence of prehistoric tsunami and earthquakes (paleotsunami and paleoearthquakes) in the geological record, and work with the global community to find new, statistically valid, geophysical estimates. The movement between the tectonic plates in the Tohoku tsunami was very non-uniform—in some areas the plates moved more than 50 metres whereas in many other areas the movement was much less, typically around 5 to 10 metres. This ‘non-uniform slip’ has important implications for tsunami, as the distribution of movement between the plates affects the motion of the seabed, which determines the size of tsunami. The probabilistic model in this report attempts to incorporate the effects of this phenomenon to a first level of approximation; this is at the cutting-edge of current science and the analysis represents a first attempt at tackling this important problem. The greater uncertainty that now exists regarding the maximum size of earthquakes on plate boundaries close to New Zealand, has led to an increase in the estimated hazard from tsunami triggered by local and regional sources. While for most parts of New Zealand the overall levels of tsunami hazard have not changed greatly from the assessed hazard levels in the 2005 report, the estimated hazard has generally increased in those areas most exposed to tsunami from local subduction zones – notably the east-facing coasts of the North Island, and the southwest corner of the South Island."
- Publication Date
- Sept. 1, 2013, 11:23 a.m.
- Category
- Geoscientific Information
- information pertaining to earth sciences. Examples: geophysical features and processes, geology, minerals, sciences dealing with the composition, structure and origin of the earth s rocks, risks of earthquakes, volcanic activity, landslides, gravity information, soils, permafrost, hydrogeology, erosion
- Regions
- New Zealand
- Responsible
- andy
- Language
- English
- Supplemental Information
- No information provided
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