Aoraki/Mt Cook. Scientists are trekking into the central Southern Alps to unlock the secrets of what remains one of the least understood fault systems in the country. Photo / Air Safaris
Aoraki/Mt Cook. Scientists are trekking into the central Southern Alps to unlock the secrets of what remains one of the least understood fault systems in the country. Photo / Air Safaris
It’s home to some of the most breathtaking scenery in New Zealand – but also thought to be capable of triggering large earthquakes.
That’s the Aoraki/Mt Cook area in the heart of the Southern Alps, where scientists plan to unlock the secrets of what remains one of the least understood fault systems in the country.
While numerous faults have been mapped there, the region’s remote, rugged and rocky terrain has made it difficult to glean geological evidence of past earthquake activity.
But there’s no doubt the area can source shakes – as shown by a 4.3-magnitude event in 2017 that gave visitors at nearby Tasman Saddle a sharp jolt – and scientists suspect it can generate quakes big enough to top magnitude 7.0.
In a new study, just awarded a $360,000 Marsden Fund grant, GNS Science earthquake geologist Dr Genevieve Coffey and colleagues plan to trek into the mountains to find which of the local faults are active, how they’ve behaved before, and what impacts future ruptures might cause in nearby communities.
“We have a number of faults that we’re really keen to focus on, but the environment and terrain is challenging to get around - and is ever-changing with weathering and erosion,” Coffey said.
The three-year study would draw on a mix of approaches: including one long used in the petroleum industry, and only recently applied to earthquakes.
This involved specific organic molecules, called biomarkers, that are deposited in sediments and gradually become part of the rock record.
“They are useful here, because during an earthquake, friction along a fault leads to the generation of very high temperatures - not unlike rubbing your hands together on a cold day - and these temperatures depend on properties of the earthquake, such as size,” Coffey said.
This map shows known active faults (in red) around the central Southern Alps, where a newly funded study will be focused. Image / GNS Science
“Biomarkers are sensitive to these temperatures and undergo structural changes as temperature increases.
“As a result, by measuring the abundance of different biomarkers along a fault we can use them to measure past temperatures, identify where earthquakes have occurred and estimate the size of these earthquakes.”
Another component involved potassium–argon (or K/Ar) dating, which scientists used to understand the timing of past earthquakes.
“It’s a technique often used to understand long time-scale problems in geology, such as understanding tectonic history,” she said.
“However, recent work has shown that if you heat a mineral up to the temperatures that occur during earthquakes, you can reset the K/Ar clock - and it can provide a record of when that material last experienced an earthquake.”
After searching for sites around Aoraki where faults were exposed at the surface, the team would collect samples and analyse them using both approaches.
“Our main hope is to fill a knowledge gap in our understanding of seismic hazard in New Zealand,” Coffey said.
“Earthquakes and their cascading effects can cause societal disruption and loss - and we really need to understand the location and size of past earthquakes in every region.”
It comes as scientists recently published data mapping nearly 900 faults capable of generating moderate to large quakes.
This wealth of information helped inform a newly updated national seismic hazard model which, compared with previous estimates, showed an increased risk of ground-shaking from future quakes in places such as Blenheim, Wellington, Napier and Gisborne.
Last week, GNS also released new maps enabling Kiwis to see the intensity of shaking caused by earthquakes measuring over magnitude 3.5.
The “Shaking Layers” maps incorporate data from ground motion sensors and are automatically produced within 10 to 20 minutes of an earthquake.
GNS seismologist and Shaking Layers technical leader, Dr Nick Horspool, said the maps’ release on the GeoNet app brought meaningful earthquake information direct into the hands of anyone with a mobile device.
“In those unsettling moments after a quake, I think New Zealanders will really value a tool designed specifically for them that offers new insights on the ground shaking they or their whānau just experienced.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
