Tuesday , March 21 2023

Our most complex earthquake: Kaikōura for two years


Scientists are still gaining lessons from the Kaikōura earthquake, two years after the shock of 7.8 has stirred the country with the equivalent release of 400 atomic bombs.

The Earth Scientist Geologist, Dr. Rob Langridge, said the event, which hit immediately after midnight on November 14, 2016, was one of the most complex earthquakes observed anywhere in the world.

This was largely due to the large number of defects that broke in just one event.

More than 20 malfunctions have been activated – of which 14 have broken violently enough to move the field by more than one meter.

Nowhere was this more dramatic than the Kekerengu Fault in Marlborough, where the pitch was offset by up to 12 meters.

In some places, the blame was visible with elevated folds of the earth that stretched across the country – called by some like Wall of Waiau.

"Another lesson was that this complex earthquake spread from one region to another – the earthquake began on the defects in North Canterbury and leaped north, triggering major mistakes in the Marlborough region," Langridge said.

"The broken faults formed a complex network of Northeast defects that were intercalated with northern defects that had a different way of moving."

Generally, the event has led scientists to consider the role of the underground Pacific plate under Marlborough.

Previously, this part of the plaque was considered to be fully "locked" or attached to the crust, but now it seemed to play a large seismic role in this part of the southern island.

Shortly after the event, Langridge and colleagues began collecting scientific data on breakdowns, landslides, sliding dams, tsunamis and liquefaction to help the community and provide advice to the government and councils.

"After a lot of data collections, we set out to publish a number of scientific papers in several overseas and local magazines, so that the acquired knowledge has a sustainable place," he said.

"We are currently trying to understand the past history of malfunctions.

"So, we have funds to go back to the defects of Paptea, Kekerengu, Hundalee, Humps and Leader and the coastal story to understand how these errors worked in previous earthquake cycles."

Much has yet to be done in several scientific areas, from seismology to geodesy based on GPS.

At Kekerengu Fault in Marlborough, near Waiau, the land was raised in some places by 12 meters. Photo / Kate Pedley
At Kekerengu Fault in Marlborough, near Waiau, the land was raised in some places by 12 meters. Photo / Kate Pedley

This summer, his team had excavated trenches over Papouth Fault to understand when he moved in the past and how much he moved over thousands of years.

This mistake has generated an incredible number of landslides in the 2016 earthquake – scientists have so far recorded a 9 m vertical movement and a 6 m horizontal movement.

"This is indeed up there on the world stage as a huge landing on land," Langridge said.

"Understanding how long it takes to accumulate this amount of tension is the key to unlocking these defects."

What remained less clear was when it could hit the next big earthquake.

GeoNet recorded more than 20,000 replies in the year following the earthquake, a few thousand more records since then.

However, only a fraction of these were greater than 3.0 in magnitude, and the number of replies continued to decrease.

The most recent forecast of the GeoNet earthquake – a statistical measure based on the probability – gave a 15% chance of a shock shock of between 6.0 and 6.9 in the first three months and a chance of 46% 12-month period.

Langridge saw the potential for future earthquakes as a time of man compared to geological ones.

"The way I look at it, we live on a plate edge that accumulates about four feet of the stalk every century," he said.

"In the distant memory, we are talking about the Awatere and Wairarapa earthquakes of the mid-nineteenth century that break some of the flaws of the plate's limitations.

"We have now seen some of the other faults in central New Zealand involved in this earthquake.

"We have to be individually prepared and as a society for the future earthquakes perspective – they are part of our makeup."

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