A swarm of earthquakes have struck off the coast of Northland over the past month but one expert said the 'big one' is not likely to follow.

GeoNet website data shows 24 earthquakes have struck in a cluster off the coast of Northland since December 17.

The two biggest were a magnitude 4.2 on January 3, 55 kilometres east of Whangārei and 12km deep and a magnitude 4.1 on January 1, 60km east of Whangārei and 5km deep.

Others were smaller in magnitude but similar in depth and distance from Whangārei.


In the same period last year, from December 17, 2017 to January 17, 2018 there were four quakes in the whole of the Northland and Auckland region, but none of those were specifically in Northland.

The seismometer at Whangārei Girls' High School. Photo/Tania Whyte
The seismometer at Whangārei Girls' High School. Photo/Tania Whyte

GNS Science seismologist Dr John Ristau said the cluster of recent quakes is what experts would call an earthquake swarm.

"A swarm is when you a get a whole bunch of earthquakes in a short period of time and focused in the same area."

He said a swarm doesn't have a big quake with smaller aftershocks but instead a couple of moderate sized quakes and then smaller ones.

"They don't happen very often in the Northland and Auckland areas. It's unusual, at the same time it's nothing to be concerned about. It happens every now and then. It does demonstrate you can have earthquakes anywhere in New Zealand."

He said the last swarm in a similar area was in February 2007. It happened further south, closer to Auckland and featured a magnitude 4.1 quake as well as smaller ones.

Ristau said the swarm of quakes were "very uncommon" for Northland, with the region having the lowest rate of seismic activity in New Zealand.

There were 19,500 earthquakes throughout New Zealand in 2018 and only 32 occurred across Northland and Auckland. Just four of those were mapped within Northland.


Ristau said by far the most likely thing that will happen with this latest swarm is that the earthquakes will happen and then everything will "quieten down and go back to normal".

"By far the least likely scenario is that something big will happen."

He said the swarm serves as a "nice little reminder that you should never just assume that you're safe".

Ristau said swarms are fairly common in volcanic regions and the north half of the north island is sitting on volcanic type areas.

Whangārei Girls High School teacher in charge of Earth and space studies Nick Major was excited to capture the cluster of off-shore quakes on the school's seismometer.

"We've never had anything quite so close to home."

The seismometer has been at the school since February last year and is part of a network of 39 in schools around the country.

Major said anything measuring over magnitude six in the south Pacific would get picked up by their seismometer, as would anything above magnitude four in the North Island.

On the day they set it up, it picked up an earthquake that struck Fiji.

As part of his lessons he gets his students to stomp next to the seismometer to get it to register the movement.

The largest earthquake recorded in Northland was in December 1963, 20km east of Kaitaia and was magnitude 4.8. It struck at a depth of 12km and hit at 1.35am.

Ristau said there were a series of quakes through to September 1964 which ranged from 4.5 to 4.8 on the Richter scale.

Another notable quake struck Maungaturoto in 1978 and a magnitude 4.3 quake struck in 1995.

In December 2003, Maungaturoto and surrounds were again shaken by a 4.4 quake at a depth of 12km, and a swarm of six small earthquakes occurred near Takou Bay in September 2006.