New research suggests there is 30% chance that a major fault line in the South Island will rupture within 50 years causing a magnitude 8.0 earthquake.
GNS Science has carried out a three-year study of the Alpine Fault and its conclusions have been published in the journal Science.
One of the authors, Kelvin Berryman, says the study found two types of faults; those which rupture randomly, as in the Canterbury earthquakes, and those which crack at regular intervals such as the Alpine Fault.
Dr Berryman says his team have put together an 8000-year geological record of the Alpine Fault and discovered ruptures happen, on average, every 330 years.
He says the last one occurred some 295 years ago, meaning there is a 30% chance of a major quake in the next 50 years.
"It could be tomorrow, it could be as much as 100 years away, but we're certainly into the window where it would not be suprising if it were to happen."
There's a definite pattern in the quakes, which were "pretty regular".
Dr Berryman says the research could be used to prioritise earthquake strengthening in areas of the world which are likely to experience large quakes in the near future.
The Alpine Fault runs for about 600 kilometres up the spine of the South Island, GNS Science says, and is the 'on-land' boundary of the Pacific and Australian Plates.