How a magnitude 8+ Alpine Fault earthquake would impact New Zealand - and where will be worst-affected

A natural disaster expert has revealed the damage a magnitude 8+ Alpine Fault earthquake would wreak on New Zealand, after new research showed such a rupture is likely in our lifetime.

On Tuesday morning, a study published in Nature Geoscience revealed there was a three-in-four chance of a large magnitude 7-plus earthquake along the South Island's Alpine Fault before 2068 - a much likelier prospect than previously thought.

The research group calculated that if a quake does hit, there's an 82 percent chance it'll be magnitude 8 or higher - meaning major damage is almost certain.

Brian Paton - Marlborough Civil Defence emergency manager and chair of earthquake education programme AF8 - told Newshub should a large quake rupture the Alpine Fault, it'll be "a national disaster that will need a national response".

"This thing is going to be much bigger than what any district can cope with on its own," he explained.

"The earthquakes are expected to go for about three minutes and the shaking varies across the South Island. In many ways, it depends which way the fault ruptures, but the worst-case scenario we're planning for is a south to north rupture."

An Alpine Fault earthquake in 1717 moved the fault line by about eight metres.
An Alpine Fault earthquake in 1717 moved the fault line by about eight metres. Photo credit: Newshub.

Such a rupture would see a significant portion of the south of the West Coast impacted, with some modelling being carried out that demonstrates shaking may be felt across the country - including "some pockets of very destructive shaking".

"Unlike the Kaikoura and Canterbury earthquake sequences, this will be South Island-wide. It'll be felt throughout the South Island and into the lower North Island as well to quite a degree."

West Coast most at-risk of Alpine Fault quake

Paton says the West Coast, home to 32,000 Kiwis, is likely to be the worst-hit area - and it won't just be the shaking they'll have to worry about.

"It will cause a lot of downstream impacts as well. We can expect a significant amount of avalanches in the Southern Alps that are going to cause road closures, take down pylons and [affect] a lot of dams as well, in behind those slips.

"It's going to be blocking off most of the roads that go into the West Coast, so they're going to be quite isolated for some time. There's also a lot of other what we call lifelines, such as power, telecom, rail - all of those could be quite severely impacted.

"So the consequences post-earthquake and the downstream hazards that occur afterwards are just as significant as the earthquake itself, in some ways."

The AF8 has recently been running a roadshow around the South Island, at which the communities expected to be severely affected are told what to expect and how they can prepare.

But Paton admits you can't prepare for some of the impacts of a magnitude-8+ quake, and planning for such a natural disaster is fraught with challenges.

Brian Paton says an Alpine Fault quake would likely go on for three minutes and be felt across the South Island.
Brian Paton says an Alpine Fault quake would likely go on for three minutes and be felt across the South Island. Photo credit: Getty

"The biggest challenge will be logistical… a lot of items that come into the country are fast-moving consumer goods, which are really just-in-time deliveries.

"So if there's no bread and milk coming over the hill tomorrow, they will pretty much run out within 24 hours of those basic items."

How to prepare for an Alpine Fault quake

Paton's advice to those in high-risk areas is to prepare a week's worth of supplies - food, water and medicine - and consider that electricity may be down for a long time.

"You might think about, 'Has the neighbour got a generator? Can we afford to get a generator?' You know, 'What alternatives are there to cooking other than electricity?' Those sorts of things.

"As you don't have any power, you can't go to the supermarket and purchase anything using your card. So having some cash on hand to do something, that's well worthwhile. 

"When an event of this size appears, you won't be seeing the emergency response people straight away. Your first responders are going to be your neighbour - so it's another really good reason to pop over the fence and meet them."