Georgia McCombe from East Coast Lab explains about the Hikurangi Subduction Zone and research into earthquakes to Dannevirke residents. Photo / Leanne Warr
Georgia McCombe from East Coast Lab explains about the Hikurangi Subduction Zone and research into earthquakes to Dannevirke residents. Photo / Leanne Warr
There is no way to predict earthquakes, not down to a matter of days or weeks, according to East Coast Labs.
But based on historical data and current research, there is a one in four chance of a major event along the Hikurangi Subduction Zone in the next 50 years.
What a major earthquake, potentially around 9.0 on the Richter Scale, could look like and how we can be prepared was the subject of a roadshow being held by East Coast Labs at venues up and down the East Coast, with two more coming up at Mahia and Hastings next week.
Project manager Georgia McCombe spoke to a small number of people in Dannevirke on the science behind the largest fault.
McCombe explained the research behind understanding earthquakes and patterns which might suggest the likelihood of a large earthquake.
Tom Ward, featuring in a German newspaper and picking up the pieces following the 1990 Mother's Day earthquake, centred near Dannevirke, owned Ward's Pharmacy, now Dannevirke Pharmacy.
Much of what is known about earthquakes has been learned in the last 50 or so years.
McCombe explains that up until the late 1960s, it was thought that the earth’s crust was solid but it was learned that it was broken up into sections - called tectonic plates.
“And tectonic plates are constantly moving. They’re moving past each other, towards each other or away from each other.”
McCombe says that the past 50 years have seen some huge technological advances but we’ve only just learned some fundamental stuff about the earth.
She went on to explain that the places where tectonic plates meet are called boundary faults and the East Coast of the North Island sits at the boundary of the Australian tectonic plate and the Pacific tectonic plate.
“Often when you hear about faults, what you’re hearing about is a crustal fault,” McCombe says.
These are like cracks in the crust or little breaks where the pressure and stress can build up.
It’s these crustal faults that can cause big earthquakes, such as what happened in Napier in 1931 and in Canterbury more recently.
In the 1970s, researchers began mapping the sea floor and found a trench that ran right off the East Coast.
This was a critical piece of learning, McCombe says.
Another was about subduction, when one plate dives down beneath the other.
“Subduction zones are important because they cause the largest earthquakes and tsunamis in the world.”
The real question for researchers has been whether we have had major earthquakes in the past and whether it means there may be some in the future.
“As long as people have been here, we haven’t had a major subduction zone earthquake,” McCombe says.
The only way to know about past major events was to look for clues in the environment.
A 110km stretch of the Kaikōura coast was uplifted following the earthquake in November 2016.
Those clues were found in marine terraces, such as in Kaikōura, where a piece of the sea floor had risen out of the ocean.
Another is in sea creatures that have died following an uplift. Researchers can take samples and do radiocarbon dating to see how old something is.
McCombe says that those clues told them that over the past 7500 years, there have been 10 major earthquakes that are bigger than anyone has ever experienced.
Given that information and more recent research, there is a 26 per cent chance of a large Hikurangi Subduction Zone earthquake in the next 50 years.
Tsunamis were also discussed in the roadshow, with McCombe offering examples of natural signs of tsunamis including tidal behaviour and an earthquake.
She related the story of a young girl on holiday with her parents in Thailand at the time of the Boxing Day tsunami in 2004, who recognised the signs of an incoming tsunami and was able to warn people.
She says the speed a tsunami moves in the deep ocean is about the speed of a jet plane and once it hits land, it’s about the speed of a car.
“So because our subduction zone is nice and close, we have about 15 minutes between a long or strong earthquake and the arrival of a tsunami.
“And this is why it’s so important that even though we live inland, we learn about it because we could be that one person at the beach who knows the signs.”
McCombe says that in the 2010s, the Hikurangi Subduction Zone was identified as one of the top three zones in the world to study by the American Science Foundation.
