Estimated earthquake and tsunami losses from large earthquakes affecting Wellington Region

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Cousins, W.J.; Nayyerloo, M.; Van Dissen, R.J. 2014 Estimated earthquake and tsunami losses from large earthquakes affecting Wellington Region. Lower Hutt, N.Z.: GNS Science. GNS Science report 2014/42 110 p.

Abstract: Building damage, repair costs and casualties have been estimated for eight large earthquake scenarios located in central New Zealand. The modelling covered the eight territorial authorities of Wellington Region. Five of the earthquakes, involving rupture of the Wellington, Wairarapa and Ohariu Faults, and the Hikurangi Subduction Zone, are considered to be the most costly and deadly earthquakes likely to impact New Zealand. The earthquakes caused shaking losses ranging from $9 billion to $17 billion over the Region, death numbers ranging from 400 to 2000 for a workday event, 140 to 560 for night-time, and injury numbers from 4000 to 10,000 workday, 3000 to 7000 night-time. The remaining three scenarios involved the Wairau and BooBoo Faults, and the segment of the Wellington Fault that runs through the Tararua Range about 40 km north of Wellington. They resulted in much lower losses and casualties. Additional losses and casualties due to subsequent tsunami were estimated for five of the scenarios. The necessary tsunami data were not available for the Ohariu and Wairau Fault cases, and the Tararua segment of the Wellington Fault was not considered for tsunami because it is entirely on-land. The tsunami made relatively modest contributions to the overall dollar losses, but often large contributions to the numbers of casualties. For a worst-case scenario involving an extreme rupture of Hikurangi Subduction Zone, with no prior self-evacuation, the numbers of tsunami deaths greatly exceeded those caused by shaking damage (3200 vs. 400 for a workday event, and 2500 vs. 150 for a night-time event). Indeed the Subduction-Cook event was the most deadly of all eight earthquakes when the shaking and tsunami inundation death numbers were combined. Two models of the Hikurangi Subduction Zone event were compared, with the sole difference between the models being whether or not the rupture extended across Cook Strait. The only significant changes in risks due to the extension of the rupture were large increases in the estimated tsunami losses, and in the deaths and injuries in Wellington and Lower Hutt. For losses, the changes were from $10 million to $1,800 million, for deaths from 25 to 3000, and for injuries from 25 to 2700. The numbers of people displaced from their homes, for times ranging from 1 day to 12 or more months, were also estimated for each scenario and for each Territorial Authority. Both short-term (1 day) self-evacuation from tsunami-risk zones, and longer-term displacement from homes damaged by earthquake shaking or tsunami inundation, were included in the modelling. About 80,000 people were expected to self-evacuate from their homes in the tsunami-risk zones in each event, with at least 60,000 being able to return to lightly or undamaged homes once the tsunami all-clear had been given. In the most damaging events, an estimated 50,000 to 70,000 people were displaced from their homes for six to 12 months and 20,000 to 25,000 people for mor e than 12 months. (auth)