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.
- Earthquake hits South Island's Alpine Fault
- Alpine Fault quake: Is the big one coming?
- Alpine Fault overdue for magnitude 8+ quake - scientists
"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.
Newshub.
