GNS Science estimates the probability of an earthquake larger than 7.8 in the next 12 months has risen to 5 percent.
The small increase is believed to be linked with the Kaikoura earthquake in November that killed two people.
GNS said the on-going slow-slip events or 'silent earthquakes' are contributing to the increased probability.
"The current slow-slip events that have followed the Kaikoura earthquake are occurring along the fault between the Australian and Pacific Plate.
Cross section of the North Island showing how the Australian and Pacific plates meet (GeoNet)
"[They] cover a large area of the plate boundary underneath the North Island and have made calculating the likelihood of future large aftershocks trickier.
"Our forecasts tell us what is likely [or unlikely] to happen in the future, but they can never definitively say if a large earthquake will occur or not."
GeoNet says it is focusing on the silent quakes connection with larger ones to help predictions.
"In New Zealand we typically have at least two or three slow-slip events each year. Scientists have only discovered in the last 15 years that slow slip events occur, so trying to understand their relationship to larger, damaging quakes is still in its very early stages."