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If the Alpine Fault line ruptures, the earthquake is expected to be felt everywhere in the country.
Over the last 8000 years, there has been a major earthquake on the fault line roughly every 300 years. The last one was in 1717.
Research shows over the last two decades, we now know that there is a 75 per cent likelihood of an earthquake on the Alpine Fault in the next 50 years, and an 82 per cent chance it will be over eight on the Richter scale.
This one — AF8, as it's called — we can prepare for.
Dr Caroline Orchiston says when you have the ground motion of a magnitude 8 earthquake, it leads to a cascading series of events.
"The mountains shake a lot which leads to landslides and they might potentially damn rivers or cross roads."
Orchiston is the science lead for the AF8 campaign — a collaboration between Civil Defence Emergency Management and Alpine Fault scientists to communicate the scientific evidence to the communities that need to hear about it.
She said scientists have determined if it does rupture, ground motions will begin in Milford Sound and roll out right along the South Island.
A surface rupture of the Alpine Fault, where the fault breaks right through to the surface, of about 350-400km is also expected.
"Movement across that surface rupture will be something like 10m horizontally and up to two or three metres vertically.
"If the fault crosses a road, a bridge or a township, that's going to be severely damaged."
Another significant consequence of an alpine fault earthquake will be on the electricity network.
Through the Arthur's Pass area, pylons take electricity from east to west and disruption could lead to prolonged power outages, Orchiston said.
New research estimates that a big quake could block South Island highways in more than 120 places, leaving 10,000 people cut off. and cost the economy about $10 billion.
Arthur's Pass is right in the middle of the Alpine Fault zone.
Chris Stewart of the Arthur's Pass Community Response said they expect to be badly affected.
"The big threat here is being blocked off. The river gets damned, possibly flooding the place.
"So we are working out how to get people out of here basically," he said.
State Highway 73 runs through Arthur's Pass, coming over a one-lane bridge at the Waimakariri River.
If the big one does happen, Stewart says they fear the bridge will be destroyed.
"We love the place and we just have to make sure that we can be prepared."
Orchison said it will not be just a West Coast earthquake.
"The outcomes of this earthquake are going to be felt right across the South Island and in fact, everyone in New Zealand is likely to feel it."
She said it is very difficult to predict the effects of an Alpine Fault earthquake on people in terms of casualties or injuries.
"We can have these things called black swan events which are very unpredictable.
"It might involve a bus travelling along SH6 being hit by a landslide, and in cases like that, we are going to get significant deaths or injuries."
For further information about AF8 visit the website and for how you can best prepare visit getready.govt.nz
• Public Interest Journalism funded through NZ On Air