Northland gets the shakes

Jun 03, 2024

A woman was jolted awake by a rare earthquake that shook some eastern areas of Northland – one of the least seismically active regions in the country.

GeoNet recorded the 4.2 magnitude earthquake at 1.38am on Thursday. It was centred 55km east of Whangarei, 12km under the seabed.

GeoNet received 82 reports of the quake being felt, most from Whangarei or from places further east.

That tremor followed a 4.1 magnitude quake just before 5pm on Tuesday, centred 60km east of Whangarei at a depth of 5km. GeoNet described that event as "unnoticeable" but did receive 102 reports from people who felt it. Several other smaller events have been reported from the same general area in the past week or so.

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GeoNet described that event as "unnoticeable" but did receive 102 reports from people who felt it. Several other smaller events had been reported from the same general area in the past week or so.

Ruakaka resident Anne Andrews said she felt a jolt as she woke up.

"The house was creaking and I always wake when I hear a slight noise," she said.

"[I] must have felt the last bit of the shake because it was more of a jolt to me."

Andrews grew up in Wellington, and said she was well aware of what an earthquake felt like and woke her partner to let him know what had happened.

GNS Science duty seismologist Dr John Ristau said earthquakes above magnitude 4.0 did not happen often in the area.

The recent events probably weren't on any fault in particular. It was just that New Zealand was being "squeezed and twisted" by the Pacific and Australian tectonic plates, he said.

"Most earthquakes will happen somewhere close to the boundary between the two plates," Ristau said. "But Northland - and Auckland - is a bit more distant from the plate boundary, but those stresses can still get transferred some distance from the boundary.

"Occasionally you can get these odd earthquakes that might pop up. There might be old faults that haven't been active for hundreds of thousands of years but are still there - these weak parts in the crust," Ristau said.

"Once they get enough stress built up within them they have an earthquake like anywhere else, but it might be a long, long time before it happens again."

A GNS report published in 2004 said earthquake risk in Northland was low. There was some damage in December 1963 from two earthquakes of magnitudes 4.8 and 4.9 near Mangonui and Peria.

Since then, there has been a 3.9 event west of Kerikeri in April 1964, a 4.4 in February 1975 near the Hen & Chicken Islands, a 3.9 event near Maungaturoto in May 1978, and a 4.3 event near the Poor Knights Islands in May 1995.

Scientists have estimated earthquakes rating as a 6 on the Modified Mercalli scale of intensities - meaning they start to cause damage to some buildings - would happen about once every 1000 years in Northland. In Wellington, they happen on average every nine years.

Occasionally earthquakes are felt in Auckland, including three shallow tremors in February 2007, centred in the Hauraki Gulf 30km east of Orewa. Those events had magnitudes of 4.5, 3.8 and 3.7, and were from 7-15km deep. They were felt from Warkworth through to Waihi.

In June 1891, a magnitude 6.0 jolt centred near the mouth of the Waikato River brought down a chimney in Onehunga, and caused minor damage to fragile items and plasterwork.