Thursday , July 29 2021

Our most complex earthquake: Kaikōura two years later

Scientists are still gaining rich lessons from the Kaikōura Earthquake, two years after 7.8 shook the country with the release of equivalent energy of 400 atomic bombs.

GNS Geologist of the earthquake of science Dr. Rob Langridge said that the event, which reached after midnight on November 14, 2016, was one of the most complex earthquakes observed around the world.

This was largely due to the large number of failures that were broken in a single event.

If more than 20 fouls were activated – 14 of which were broken violently to slide the ground for more than one meter.

On no side this effect was perhaps more dramatic than during the failure of Kekerengu of Marlborough, where the land was compensated for up to 12 meters.

In some places the fault was visible with the folds raised from the ground that extended by the field, bent by some like the Waiau Wall.

"Another lesson was that this complex earthquake spread from one region to another – the earthquake began to fail in North Canterbury and jumped north, causing major failures in the Marlborough region," Langridge said.

"The faults that were broken formed an intricate network of flaws that surrounded the northeast that intertwined with flaws in the north, which had a different mode of movement."

More broadly, the event led scientists to consider the role of the Pacific Plate sub-party under Marlborough.

Previously, this part of the plate was thought to be completely "blocked", or attached to the crust, but now it seemed like it was playing a great seismic role in this part of South Island.

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

"After many collected data, we began to publish a series of scientific papers in various foreign and local magazines, so that acquired knowledge has a long-standing place," he said.

"We are currently looking to understand the past history of flaws in some of these faults.

"So, we have funding to go back to Papatea, Kekerengu, Hundalee, Humps and Leader faults and coastal history, to understand how these flaws worked in previous earthquake cycles."

There is still a lot of work to be done in various scientific areas, from seismology to geodesy based on GPS.

In the Kekerengu fault of Marlborough, near Waiau, the land was raised in some places for 12 m. Photo / Kate Pedley
In the Kekerengu fault of Marlborough, near Waiau, the land was raised in some places for 12 m. Photo / Kate Pedley

This summer, his team would be digging trenches along Papatea's fault to understand when he moved in the past and how much he changed for many thousands of years.

This failure launched an incredible amount of slip into the 2016 earthquake, as scientists recorded up to 9 m of vertical movement and 6 million horizontal movement.

"This is really there on the world stage as a great earth trip," said Langridge.

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

What became less clear was when the next major earthquake could strike.

GeoNet registered more than 20,000 replicas in the year following the earthquake, with several thousands registered since then.

However, only a fraction of these was greater than 3.0 in magnitude, and the series of replicas continued to decline.

The latest earthquake forecast for GeoNet that shakes the medal – a measure based on statistics that calculated the probability – gave a 15 percent chance of a replica between 6.0 and 6.9 delayed in the next three months , and 46% the chances of this happening at some point to a 12-month period.

Langridge saw the potential for future earthquakes as a case of comparison of human and geological times.

"As I look at it, we live on board a limit of plates that accumulates about 4 m of stress every century," he said.

"In distant memory, we talk about Awatere and Wairarapa earthquakes in the mid-nineteenth century that break some of the important failures in the borders of the plate.

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

"We should only prepare individually and as a society for the prospect of future earthquakes – they are part of our makeup."

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