6 Jun 2023

Alpine Fault's potential dangers are real, but still unknown

2:33 pm on 6 June 2023

By Lois Williams of Newsroom

The Alpine Fault is marked out on satellite images by the western edge of the Southern Alps snowline.

The Alpine Fault is marked out on satellite images by the western edge of the Southern Alps snowline. Photo: NASA

Inhabitants of the shakiest part of Aotearoa's shaky isles are readier than ever for the overdue big one.

West Coasters turned out in their hundreds this week to hear scientists remind them they face disaster when the Alpine Fault decides to rearrange the scenery.

The AF8 roadshow has just completed its biennial tour of the region, updating schools and communities on the latest science has to offer on the magnitude 8 - or greater - earthquake predicted to hit the South Island within decades.

The good news is the Coast is probably better prepared than ever for the expected catastrophe.

Core samples from West Coast lake beds in recent years show the giant fault along the spine of Te Wai Pounamu has ruptured with remarkable regularity every 260 to 300 years.

The last event was in 1717, making the next big one well overdue.

"The fault is very close to rupturing," seismologist Caroline Holden told an audience in Greymouth's Civic Theatre.

"It's very active and it's producing a lot of clues about what the next quake will be like."

It is in fact producing a "hum" the scientists say - a low background noise reflecting the vibrations of the dynamic processes at work deep within the earth.

Holden and colleagues from Victoria University and GNS Science have their ears to the ground via the SALSA project, an array of seismic sensors installed the length of the long skinny part of the fault line from Milford Sound to Maruia.

Hence the project's name: Southern Alps Long Skinny Array.

The data they are collecting reveals how various parts of the fault are being stressed as the earth's tectonic plates slide and collide, the Pacific plate on the east and Australian on the west.

Project lead John Townend says the field study, which ends in November, will yield valuable information about how and where the ground moved in small quakes.

But it cannot foretell the big one.

"It won't help us predict an earthquake, where the epicentre will be or how deep," Townend says.

"But it'll give us a much better handle on what ground motions to expect when it comes.

"What we do know is AF8, the Alpine Fault rupture, is going to be very long and very complex and there will be very strong aftershocks."

The entire South Island - the whole country in fact - will be affected, the scientists warn.

But the Coast, a long mountainous strip from Haast to Karamea whose eastern boundary is the fault line itself, will be hit hardest.

In a magnitude 8 quake - remembering Kaikōura was 7.8 - mountains will crack, landslides will dam rivers and block roads and fissures will split the ground beneath farms and towns wrecking houses and trapping motorists.

Injuries and fatalities are expected.

On the bright side

Best then to be ready, as AF8 programme manager Alice Lake-Hammond cheerfully points out.

"This can all be quite confronting. But looking on the bright side, without the alpine fault and the big earthquakes of the past we wouldn't have our mountains and this beautiful place we live in.

"I find it helps to think about that."

The Greymouth audience listened politely to the scientists' presentations on the seismology and research.

But their questions revealed a preoccupation with the practical and specific: Is there a map showing earthquake risks in a given area or community, one man asked.

Answer: not really.

It is hard to identify those when no one can tell how the earthquake might affect a particular locality.

What about the reservoirs above Kumara? Would they come crashing onto homes below, a resident asked.

No one knows exactly.

The AF8 roadshow's been going since 2016, involving scientists, South Island councils and civil defence agencies from around the motu.

And despite the unknowns and unknowables, since its last visit to the West Coast two years ago a lot's been happening to prepare for what will be the biggest natural disaster to strike the region in 300 years.

The region is in fact used to big events and, acutely aware of the risks of isolation, may be the best prepared in the country, according to emergency management regional manager Claire Brown.

It started by beefing up its means of regional communications.

Stars align

"We were the first to hook into Starlink - a year ago now. In fact we sent our Buller devices to Hawke's Bay to help them out.

"We have Starlink in all our emergency management centres, plus 16 in Buller, seven in Grey and 18 in Westland."

Isolated households with poor internet connections should think about buying a Starlink system, Brown says.

"It's come right down in price and could be a life-saver in an emergency."

Under the regional council banner, Civil Defence has strengthened its radio network from Karamea to Jacksons Bay, installing a VHF repeater in South Westland and putting in place links with other organisations that rely on radio communications including the Department of Conservation.

Flying along the Alpine Fault towards Theta Tarn, on the edge of the Olivine Wilderness Area. Photo:

Generators have been positioned throughout the region, including three large mobile units on trailers and mobile fuel pods are ready to be airlifted to remote areas.

Petrol stations have been set up to run on generators and a secure emergency fuel supply created.

A cache of emergency supplies including a shipping container with everything needed to run an emergency response is ready and waiting in Greymouth.

Community civil-defence committees are in place and more than 100 people in key Coast businesses and organisations have had emergency management training so they can be called on if the worst happens.

Be prepared

"We'd encourage families and businesses to think now about what they'd need in their homes or vehicles to get by for at least a few days if they're stranded," says West Coast Regional Council chair Peter Haddock.

"The Coast could be cut off by road for weeks."

Haddock, who lives on a lifestyle block, is a prepper from way back.

"I have a generator and I always like to have about eight full gas bottles on hand.

"When I travel - Coasters drive a lot - I always have a spare set of warm clothes, some sturdy boots and supplies.

"You never know where or when you might have to spend a night in the car."

Buller Mayor Jamie Cleine - who's fronted more than his share of flood emergencies in the past two years - says the AF8 roadshow is sobering in its message of what lies ahead.

The Westport theatre was almost full for this week's event.

But it's not about scaring people, he says, so much as facing reality and doing all that can be done to prepare.

"I'd say we're 100 percent better prepared than a few years ago but we have to keep improving.

"It's all we can ask for and the best we can do, really."

This article was originally published by Newsroom.

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