A big earthquake on the Alpine Fault is overdue and one expert says it’s New Zealand’s “big elephant in the room”.
Running 600km along the Southern Alps, it marks the boundary of the Pacific and Australian plates.
The geological record dates back 8000 years and from that we know there’s been an earthquake on the fault about every 300 years.
The last one was in 1717 – and the next could happen at any time.
“We are quite late in the typical cycle of the Alpine Fault’s big earthquakes,” John Townend, a professor of geophysics at Victoria University, tells The Detail.
“It doesn’t mean an earthquake is imminent tomorrow or next week, but it does mean that compared to the long-term behaviour of the fault we are in a fairly late stage.
“That is something that causes us legitimate concern but on the other hand, we can prepare for that.
“This is the time, really, for communities, scientists and engineers to be thinking ahead – thinking about what it might mean if the earthquake were to unfold the way we think it might.”
SALSA and SISSLE
Townend is one of the academics leading two key research projects to work out what might happen when the earthquake hits.
“We know the Alpine Fault produces big earthquakes, but we haven’t seen one ourselves in recorded memory,” he says.
“Will it start in the south and rupture to the north? Will it go very deep? Will it rupture very slowly or very quickly? These two experiments are really intended to address these questions.”
The first project is SALSA, or the ‘Southern Alps Long Skinny Array’.
“We’ve called it that because we have put out an array of seismometers – it’s about 450 kilometres long – and it’s quite skinny. Each of the instruments are placed within about two or three kilometres of the Alpine Fault,” Townend says.
“We’re using that to record two types of signal. One of them is very small earthquakes and other characteristics of the fault … the other thing we’re recording is the background noise or hum of the earth. Using that background hum, we’re able to extract very valuable information that tells us how [a] slip on any one point on the fault might cause shaking at points throughout the South Island.”
Most of these seismometers were put in place in November 2021 and are due to be taken out in about six months.
The second project is called SISSLE, the ‘South Island Seismology at the Speed of Light Experiment’, which piggybacks on fibre internet cables.
“We are using a laser system attached to optical fibres, installed by Chorus for telecommunications purposes, to record seismic waves,” Townend says.
“We are recording signals that are travelling through the fault zone – from earthquakes happening nearby and even from earthquakes happening very far away.
“We really want to understand what is the internal geometry, what is the structure of the fault – is it kinked, is it bent – does it have multiple different strands to that … those sorts of things that will affect the way that an earthquake rupture will eventuate.”
Preparing for the big one
Jamie Cleine is the mayor of the Buller District, which is likely to be completely cut off in a big Alpine Fault quake.
“Districts like mine have relied a lot on external resource being able to come in to assist us in [previous] emergency responses,” Cleine says.
“In AF8 [Alpine Fault 8 magnitude] that’s unlikely to be the case, because everyone will be in a similar boat. AF8 preparedness is hugely focused on coordinating resources locally and making sure people are educated on what they can do for themselves. For the first, at least a week most likely, the district will be on our own.”
Cleine is the chair of the region’s joint council civil defence committee. He says there’s a lot of work going into communications region-wide.
“West Coast Emergency Management have deployed StarLink [wifi internet] devices right throughout our district, to all our emergency operations centres, but also various marae and community centres. They’ve also beefed up the UHF radio so the older-school radios, making sure those networks are still available and they’re looking at HF, which is probably again an older technology able to communicate beyond the region.”
He says there’s also work going into the supply of generators and fuel.
But one of the problems is the cost.
“It’s not going to be affordable on our own, that’s for sure but there are some big challenges for New Zealand Inc. in terms of adapting to climate change. .. AF8 is in another league compared to a localised flooding event… in terms of affordability it’s the constant issue we have on the West Coast.”
There is a role for central government, but Cleine says the Buller District has also partnered with GNS Science and the Ministry of the Environment to help with some of the science costs.
“Are we ready for AF8, as a council or as a region? My answer’s ‘no’, but we’re an awful lot better prepared than we were 12 months ago and probably triple more prepared than we were three or four years ago. It’s about incremental improvement.”
Hear more about how the West Coast is preparing for the big shake by listening to the full podcast.
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