Combined Tsunami and Earthquake Loss for Wellington, New Zealand

Abstract eng:
Shaking damage arising from rupture of the Wellington Fault has long been regarded as being the Probable Maximum Earthquake Loss for New Zealand. Recently, however, this has been questioned following a probabilistic study of potential tsunami losses, which suggested that tsunami losses could greatly exceed earthquake losses for all levels of probability. With this in mind, we are aiming to estimate the combined earthquake plus tsunami PML for New Zealand. Whereas the tsunami risk is relatively evenly spread over the length of New Zealand, the Wellington region by far dominates the earthquake risk, hence is likely to be the location of the greatest combined earthquake/tsunami risk. Modelling has therefore concentrated on potential tsunami-genic earthquakes in the Wellington Region. Five preferred sources have been modelled, including • Wellington Fault (magnitude 7.5, highest earthquake loss of $12± 5 billion for an exposure of $77 billion), • Wairarapa Fault 1 (magnitude 8.2, high earthquake loss, last ruptured in 1855 causing a tsunami, with this study calibrating well with the historical wave-height data observed). • Subduction Zone (a likely major tsunami source, various models possible, but Wellington somewhat shielded from the tsunami by topography). The overall results of the study have been confirmation that the maximum credible loss of Wellington remains dominated by earthquake shaking damage from the Wellington fault earthquake, with additional losses from tsunami from that event being negligible. Tsunami damage from other near field events could be appreciable but still much less than the Wellington earthquake shaking damage.

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