Experts warn magnitude 9 earthquake could wreak havoc along New Zealand's east coast

  • 10/10/2022
A map showing the zone.
A map showing the zone. Photo credit: GNS Science / Supplied

A magnitude 9 earthquake could potentially wreak havoc along the east coast of New Zealand, experts say.

Researchers studying the region say there is a one in four chance of a 'megaquake' occurring along New Zealand's largest fault line within the next 50 years.

One of New Zealand's most powerful earthquakes in the past was the 2016 Kaikoura earthquake which was 7.8 on the Richter scale. Meanwhile the infamous 2011 Christchurch earthquake measured 6.3.

Dr Kate Clark from GNS Science said advances in science have allowed forecasting for major subduction zone earthquakes - which could see magnitude 8 and 9 earthquake events.

''We did a study at Lake Grassmere in Marlborough and at that site we found evidence of two really large tsunamis. One was about 1500 years old and one was about 2000 years old," she said.

"And that's the first time we've been able to calculate what the frequency of large earthquakes on the subduction zone is."

Dr Clark said chances are high for a large earthquake to occur on the southern portion of the plate boundary.

"One of the big advances we've made in five years is having a better forecast of when the next large subduction earthquake is likely to be. So for most of us - definitely our children, there's a one in four chance that this will happen in their lifetimes."

The Hikurangi subduction zone (HSZ) stretches from the northeast of the North Island, past Hawke's Bay, and tucks underneath the Australian plate.

Ben Greene, Civil Defence and emergency manager in Gisborne, warned that residents in the Tairawhiti area need to be prepared for such a disaster.

"As a region we are isolated. The type of event that Hikurangi will present - it'll be multiregional. So support in that essence won't be a helicopter turning up within 12 hours. We need to be resilient for a period of time."

Dr Laura Wallace, a geophysicist from the University of Texas, said offshore earthquakes pose the greatest threat to New Zealanders.

Enough movement on the seabed could trigger large tsunami waves, "which is really the greatest concern for the potential of loss of life", she said.

"The area along the Hikurangi subduction faultline is one of New Zealand's largest sources of earthquakes and tsunamis. Because of GeoNet we are able to monitor what is happening on the subduction zone - the part of it that is beneath our feet, but we really are blind about what is happening on the offshore part - and that is the most dangerous."

Dr Wallace is part of an international team studying slow slip events which are slow-motion earthquakes that can take days, months and even years to occur.

In a ground-breaking study involving a multi-national team of geophysicists and oceanographers, scientists are deploying a large number of sensors to the seafloor along the HSZ. They aim to improve the understanding of vertical movement of the ocean floor during slow slip events in greater detail.

Researchers have come from Columbia University and the University of Rhode Island in the USA, and the University of Tokyo, Kyoto University, and Tōhoku University in Japan, to join GNS Science researchers on the NIWA research vessel Tangaroa.

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