A slow-slip "silent" quake under the North Island's East Coast has been triggered by last Monday's massive Kaikoura earthquake.
Monitoring equipment has detected a large ongoing slow-slip deep below the Earth's surface under Hawke's Bay and Gisborne.
The silent quake has moved GPS stations 2-3cm.
GNS scientists believe the unfolding quake, which could last months, was triggered by passing seismic waves from the 7.8 earthquake.
In a blog on the GNS website scientist Laura Wallace said the waves may have caused stress changes in the Earth's plates and sparked the silent quake.
The quakes are undetectable to humans and seismographs.
Wallace posted in the days following last week's Kaikoura earthquake a slip was triggered along the plate boundary where the Pacific meets the Australian Plate from Hawke's Bay up to East Cape.
She said slow-slips had previously happened in these regions, but they had been separated in time or happened one after the other.
GNS Science, GeoNet and scientists were keeping a close eye on the slip.