Alpine Fault: 'High probability' of magnitude 8 quake in next 50 years

An earthquake on the Alpine Fault on Sunday has renewed calls from GeoNet for the public to be ready for a larger, more devastating shake - but what are the chances it will occur in the next 50 years?

On Sunday morning, a 5.5 magnitude quake struck near Milford Sound at a depth of only 5km, waking Queenstown residents and prompting a reminder from GeoNet about the potential of the Alpine Fault to rupture.

"This fault system has the potential for larger events and we would like to make sure that you are prepared for a large earthquake at all times," GeoNet tweeted, before telling the public to be aware of advice from Civil Defence.

The last time the Alpine Fault had a major rupture was in 1717, when a magnitude 8.1 earthquake hit the South Island.

In 2012, research from GNS Science said there was a 30 percent chance a large, magnitude 8 quake will occur in the next 50 years on the fault.

On Tuesday, a GNS Science spokesperson told Newshub that 30 percent was still the current probability.

GNS Science refers to this as a "high probability" and the rupture would "produce one of the biggest earthquakes since European settlement of New Zealand".

That prediction first came after scientists studied an 8000 year-long record of 24 Alpine Fault earthquakes based on data gathered near Lake McKerrow, northeast of Milford Sound.

It found that the average time between large earthquakes was 330 years - although some historical quakes studied did have intervals in the range of 140-510 years.

But Sunday's quake is unlikely to have made a larger quake more or less likely.

Geologists say you generally can't predict whether a big quake is about to happen based on smaller foreshocks -  while many large quakes are preceded by smaller ones, just as many aren't.

Nor do small shocks reduce the chance of a big one happening - they're just not strong enough to release the tension.

"We can't say that a big one is not on the way, but we don't believe that this quake has significantly increased the chance of a big one," GNS Science duty seismologist Sam Taylor-Offord told Newshub on Monday.