Faultline load could cause giant quakes

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 said while the research was ‘‘well-founded’’, there was 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 magnitude 8.2 quake 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 report from 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 fault line 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

‘‘Their extreme larger size questions our understanding of fault and earthquake physics.’’

Scientific Reports

Researchers in understanding physics.’’

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

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 quake would have created additional pressure on Wairarapa faults, a major quake could still be decades away, he said. Giant earthquakes on the Wairarapa fault, such as the 1855 quake, had an average repeat time of about 1300 years. This meant there was about a 1 to 7 in 100 chance of ‘‘giant earthquake’’ in the next century, he said.

The conclusion in the paper that the fault ‘‘may be prone to break’’ went beyond what the data supported, he said.

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