‘Giant earthquakes’ predicted

The Wairarapa faultline may be at breaking point, researchers warn

Cracks beneath Wairarapa have been put under new pressure by the 2016 Kaiko¯ura earthquake, increasing the potential for ‘‘giant earthquakes’’ that could damage large swathes of the country.

New research has found the 2016 Kaiko¯ ura quake had ‘‘loaded’’ the Wairarapa faultline to the north, which may now be at breaking point.

However, Geonet has warned that while the research was ‘‘wellfounded’’, there remained only a ‘‘very low’’ chance of a giant Wairarapa earthquake in our lifetime.

The Wairarapa faultline is responsible for New Zealand’s most severe earthquake since colonisation. In 1855, a magnitude8.2 earthquake killed nine people, causing severe damage from Whanganui to Kaikoura and generating a tsunami.

That quake was so severe that it remade much of the Wellington and Wairarapa coastlines, raising the ground by as much as 2.7 metres. Wellington’s Basin Reserve cricket ground is built on land lifted by the quake.

The study by European researchers, published in Scientific Reports this month, says the key to predicting the size and damage of potential earthquakes is to know the size of previous large earthquakes on that fault.

It found the Wairarapa faultline had ‘‘repeatedly produced giant earthquakes and is likely able to produce a similarly strong forthcoming event’’.

‘‘Past earthquakes were dramatically large. Beyond the high seismic hazard these large earthquakes pose in New Zealand, their extreme larger size questions our understanding of fault and earthquake physics.

The new report also described the Wairarapa faultline as ‘‘fast slipping’’.

This means that ‘‘stress loading’’ caused by the Kaiko¯ura earthquake, and the deformations observed at the Wairarapa faultline, may be bringing it ‘‘closer to failure’’, the report said.

‘‘If a similar earthquake were to occur today, it would initiate where stresses have been amplified by the 2016 Kaiko¯ ura earthquake.’’

The possibility of an earthquake on the Wairarapa faultline in the near future needed to be considered, it said.

Jeremy Holmes, regional manager at the Wellington Region Emergency Management Office, said an earthquake from the Wairarapa fault would affect Wellington greatly.

Links between faults, like Kaiko¯ura and Wairarapa, were being discovered all the time, he said.

‘‘But earthquake prediction is not an exact science ... we just have to be mindful that it could put pressures on [the Wairarapa fault] and it could cause an earthquake at any time,’’ Holmes said.

GNS Science natural hazards and risks leader Kelvin Berryman said the paper was ‘‘well founded’’ and reinforced previous research by GNS Science and Victoria University.

While the Kaiko¯ura earthquake would have created additional pressure, a major earthquake could still be decades away, he said.

Giant quakes on the Wairarapa fault had an average repeat time of about 1300 years. This meant there was about a 1 to 7 in 100 chance in the next century.