Thousands of people have reported feeling the jolt.
It was a magnitude 3.2.
Two years' worth of data was collected and it could be used to link slow-slip earthquakes to seismic events.
Here's what we know.
More than 1000 people have already reported feeling the quake, from Wellington to Warkworth in Auckland.
Specialists have been analysing the data collected from deep ocean tsunami sensors, tide gauges, and eyewitnesses.
"Earthquakes that generate tsunami impacting the northern part of NZ are possible in any of these scenarios."
"The community took action pretty well."
All three earthquakes happened along the Tonga Kermadec subduction zone.