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Earthquake model puts Wairarapa in the danger zone


The brighter the colour indicates the more the ground would move in an earthquake. PHOTO/SUPPLIED

Wairarapa is at greater risk of serious damage than most of New Zealand should an earthquake strike, and insurance costs could be taking an upward turn.

The National Seismic Hazard Model [NSHM], made public this week, considers possible earthquakes that could affect a location and then estimates the severity of the related shaking that might occur.

Higher levels of ground shaking would mean an increase in the chances of landslides, ground cracking, people being thrown and land features changing.

The model has predicted a 50 per cent average increase in the chances of ground shaking strongly across New Zealand, with Wairarapa forecast to experience up to three times as much shaking as previously expected.

That makes it one of the regions likely to rattle the most in a revelation that would have implications in building codes, infrastructure, and insurance.

NHSM project lead Matt Gerstenberger said the model meant we now knew a lot more about earthquake hazards and their impacts than we did previously and could use it to better prepare.

“The model assesses the earthquake hazard in different locations throughout New Zealand. Hazard varies throughout the country, based on the geography and ground conditions, and the frequency and types of earthquakes that might occur in each location. Hazard also varies within regions.

“The model doesn’t give a single estimate of ground shaking hazard, it provides a range of results across locations, so there is no one number that can be referenced when it comes to describing the hazard and no one set of results. All the information needs to be considered together,” he said.

“Wairarapa is situated over the Hikurangi Subduction Zone, which is a really important fault that the NSHM takes into account. Across New Zealand, the average hazard change is about 50 per cent or more. While Masterton’s range of hazard is forecast to be between no change and up to three times, in most cases that change will be around 50 per cent or more.”

Insurance Council of New Zealand spokesman Christian Judge said the amount of data available meant it would take a long time for homeowners to see any changes in insurance costs.

“Don’t expect any immediate change. These things will take time to work in.

“The model shows what the risk is of a particular thing happening. One thing is how likely is an event to occur if this fault gave result to a magnitude ‘x’ earthquake.

“Some frequencies cause liquefaction, some cause real problems for houses and others problems for tall buildings.

“And that information is available in a way it never was before.”

Judge said the information was a valuable resource that would improve the safety of communities around New Zealand.

Gerstenberger said the NSHM provided shaking information to agencies that would now be able to assess infrastructure risk. The model would also have implications on earthquake safety standards for the building and construction industries.

“Knowing how future earthquakes might affect our regions helps us understand the risks to our communities, and helps government, industry and the New Zealand public prepare well.

“Lots of agencies that think about earthquake shaking risk will be considering the model and how to apply the information in their planning and policy.

“This is more sophisticated science than we have ever had before for them to work with, and it will take some time to consider the detail the model provides.”

George Shiers
George Shiers
George Shiers is a reporter at the Wairarapa Times-Age interested in politics and social issues. He reports regularly on a range of topics including infrastructure, housing, and transport. George is also the Tararua reporter and helps cover police, fire and court stories.

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