A magnitude 7.6 earthquake striking Wellington during the day could kill hundreds, destroy 600 buildings and cost nearly $20 billion to cleanup, new research predicts.
The devastating projections are revealed by disaster prediction software, which scientists use to simulate the likely fallout from catastrophic natural disasters.
It is hoped the RiskScape software, developed in Wellington, will soon provide accurate projections for other disaster events such as landslides, windstorms and tsunamis to help emergency response agencies prepare for the real thing.
"We all know we live on a major fault, but this modelling helps us understand how a worst case scenario could affect our city," GNS social scientist Kim Wright said.
If "the big one" hit, fracturing Wellington's main active fault, the modelling shows hundreds would be killed, hundreds more seriously injured and 29,000 displaced in the immediate aftermath of a big earthquake.
The number of collapsed and severely damaged buildings would be worst in the densely populated central business district and eastern suburbs.
The 80 kilometre Wellington-Hutt Fault starts in Cook Strait and runs through Karori and the CBD to the Hutt Valley where it stops at Kaitoke in the Tararua Range.
The fault is thought to be prone to periodic rupturing based on geological research.
Research from 2010 shows this southern stretch of the larger Wellington Fault - which extends to the Bay of Plenty - ruptures to magnitude 7 or above about every 900 years, and it last reached that intensity about 300 years ago.
The model was calculated using software being developed by GNS Science and the National Institute for Water and Atmospheric Research in Wellington.
Wright said the RiskScape modelling was not yet fully fine-tuned - especially with casualty forecasts.
She also warned against thinking of the software as only useful in a worst-case scenario.
"RiskScape is not just about worst-case scenarios - it's about understanding all kinds of risks and how we can reduce their impact."
The software could help scientists, asset managers and risk forecasters better understand natural hazards before disaster struck so planners and agencies like Civil Defence, power companies and councils could try to stem the fallout for people and the economy, she said.
It would eventually be distributed free to disaster response and other not-for-profit agencies.
RiskScape tests for a host of hazards, including earthquakes, river flooding, tsunami, volcanic ashfall and windstorms, and calculates replacement costs, casualties, economic losses, disruption to infrastructure and business, and number of people affected.
It is also being tweaked for use in forecasting landslides, coastal storm-tide inundation, volcanic lahars, snowstorms and climate change effects.
Potentially the software could become the industry standard for hazard and impact assessment, and it was hoped it would grow "organically" once other agencies started plugging in their own disaster mapping data, Wright said.
Regional and local councils in quake-stricken Canterbury, plus the West Coast and Hawke's Bay have been partners in the project.
Wellington City Council also planned to get on board, and would likely use the software to find the best spots for emergency shelters after a disaster.
WCC spokesman Richard MacLean said the software would be extremely helpful for disaster planning and response purposes.
Council officials would talk to GNS and Niwa about how the material could be used to help prepare for natural disasters across the region.
"We are going through a lot of changes at the moment in terms of Civil Defence, and this will be tremendously useful."
Because of the challenging nature of Wellington's geography, there were obviously places that were more or less risky and the more accurate predictions could be, the better, he said.