A magnitude-8 quake could hit New Zealand’s South island within 50 years, according to research by GNS Science and the University of Nevada, Reno.

It says the 600km Alpine Fault, which runs along the alpine spine of the South Island from Marlborough in the north to Milford Sound in the southwest, produces a quake on average every 330 years.

“Our research shows there is a 30% chance of an earthquake in the next 50 years,” GNS researcher Ursula Cochran told insuranceNEWS.com.au.

The last recorded quake on the fault was in 1717.

The Alpine Fault has been studied for many years but the latest assessment comes from study of the last 24 earthquakes where previously only four were studied.

“We went back 8000 years while previous research had only gone back 1000,” Dr Cochran said.

The research breakthrough comes with the carbon-dating of leaves and seeds at two sites near Milford Sound, producing one of the world’s best records of regular fault rupture.

Scientists found that fault ruptures did not occur randomly or in clusters but at regular intervals that average 330 years but could be as often as 140 years or as rarely as 510 years.

While quakes along the fault are stronger than the 7.1 and 6.3-magnitude earthquakes that struck Christchurch in the past 22 months, they would be too distant to damage the city.

“They will affect the whole of the west coast of the South Island, which has a population of between 40,000 and 50,000,” Dr Cochran said.

The research shows the next quake could be very close or as far away as 100 years, but “it will inevitably happen and the more preparation done now the better,” Dr Cochran said.