Likelihood of strong-shaking earthquakes increasing nationwide

Source: 1News

A GNS review into the modelling used to predict just how much the ground shakes in earthquakes has been released, with big implications for building, infrastructure and insurance policy.

The National Seismic Hazard Model (NSHM) has forecast a 50% increase on average in the chances of the ground shaking strongly across the country, and Wellington and the Wairarapa are among the regions likely to feel it the most.

The model has been revised for the first time in 20 years and uses data from past earthquakes like Kaikōura and Canterbury, combined with the latest technology.

Earthquake damaged building in Christchurch.

Lead seismologist Matt Gerstenberger says the new NSHM provides the most up-to-date modelling and understanding of earthquakes in the scientific community.

"We have more evidence of how complex ruptures can be and that they don't just have one fault that can rupture on its own," says Gerstenberger.

"It's quite common in New Zealand earthquakes that they join up and we have multiple faults that come together. This means they can link across larger regions and we have bigger earthquakes."

The review of the NSHM was commissioned by the Ministry of Business, Innovation and Employment (MBIE) and the Earthquake Commission (EQC).

According to MBIE's building performance and engineering manager Dave Gittings, the complexity of the changes means it will take some time to adjust building regulations.

"It will likely modify building design for new builds. There's no proposal to change the earthquake prone building regulatory system. That will remain as is," says Gittings.

"New builds will continue to happen. We would recommend just using current loading standards until we can find a way to use this complex information and fold them into the regulatory settings."

MBIE's chief engineer Ken Elwood says his department is working with Engineering New Zealand to also understand what changes may be necessary.

"It really is going to lead an evolution to our approach to design," says Elwood.

"When we learn new things about hazards around us, we adapt. In the great earthquake in Hawke's Bay in the 1930s we learnt that unreinforced masonry buildings didn't perform well, so we stopped building them."

Insurance Council chief executive Tim Grafton says the revision is an important piece of work and it will take several months before any advice changes for its members.

"Since Christchurch and Kaikōura we've already seen insurers have a deeper understanding of the risks in New Zealand," Grafton says.

"And as a result of that, we've seen price adjustments going back three or four years. So all we're looking at now is what is new that we don't already know, that might influence our decisions in the future."