In its latest update on the Kaikoura quake, which was 7.8 in magnitude, Geonet said that while it can't predict tremors, it could provide forecasts of future aftershocks based on probabilities and possible scenarios.
The quake struck just after midnight on November 14, causing widespread damage to roads and property in the region, as well as in Wellington.
Geonet said the most likely scenario was that aftershocks wouLd continue to decrease in frequency over the next year and no aftershocks of magnitude 7 or larger would happen.
Felt aftershocks (those over magnitude 5) would occur in the area from North Canterbury to Cape Palliser/Wellington.
It was very likely (98%) that within the next year, there would be at least one aftershock of magnitude 6 to 6.9 in the next year, regardless of there being a larger (magnitude 7.0+) earthquake.
There was a 54% chance of a quake of that size occurring within the next month.
Most aftershocks of the Kaikoura quake were occurring throughout a broad area from North Canterbury through to Cook Strait that surrounded the faults that ruptured in the November quake. Although a few had occurred in the lower North Island.
Geonet gave predictions for three possible scenarios.
"Some of these may be more unsettling to you than others," it said in a blog post.
"We recognise that while these scenarios may increase anxiety the best thing is to be prepared. Remember: To drop, cover and hold in an earthquake. If you feel a long or strong earthquake and you are on the coast, evacuate immediately.
The probability of "damaging earthquake shaking from" aftershocks over the next 20 days around the wider Kaikoura/northern East Coast of the South Island, was around 30 to 40%.
The probability in the Wellington area was less than 2%. Christchurch's aftershock probabilities were not greatly affected.
A tsunami was created by the Kaikoura quake, and scientists were still analysing the tsunami data and collecting information on its impacts.
"Remember, if an earthquake is too strong to stand up in, or lasts longer than a minute, move inland or to higher ground immediately,"Geonet said. "Do not wait for a siren or an official warning."
The earthquake caused thousands of landslips in North Canterbury, Kaikoura and Marlborough, which remain dangerous and could move at any time.
Landslips had also dammed several rivers and could breach, particularly in heavy rain.
