Whangārei coast shaken but not stirred after quakes

Tutukaka resident Steve Marshall.

Tutukaka resident Steve Marshall.

A map showing where a cluster of at least seven small earthquakes have been recorded.

A Sandy Bay resident said an early morning earthquake yesterday felt like a underground ultrasonic wave hurtling toward the house ''and then the Incredible Hulk jumped on the deck''.

Casey Meredith said the initial sound followed within seconds by a sharp shake had woken him with a jolt.

''I hadn't felt the earlier ones but I certainly felt this one. It felt like something just slamming into us.''

One Tree Point resident Russell Foster was also jolted awake by the house shaking.

The bed juddered backwards and forwards, ornaments rattled and a mozzie spray fell off a table.

''I'm a Northlander and I've never lived in an earthquake zone so it's not the first thing to come to mind when you feel it,'' Foster said.

Once the motion stopped, he went outside to see if the tsunami sirens were sounding or there was any other local reaction. There wasn't, and he went back to bed.

Just over an hour later he felt another, smaller tremor.

Foster was among hundreds of people from Tutukaka to Bream Bay and as far inland as Puhipuhi either woken yesterday morning or who felt other quakes in the evening on January 1, at 7.10pm and 10.48pm.

The later one on Tuesday night was of 4.2 magnitude, located 60km east of Whangārei and 5km deep.

Carol Clegg at Matapouri Bay was woken by the one at 1.48am yesterday.

''Blinds were swaying and furniture shaking. I woke my husband up who thought I was imagining it a few days ago when I felt a rumble. He definitely felt this one.''

The cluster of minor quakes since late December has become quite a talking point with locals and holidaymakers.

Tutukaka man Steve Marshall has been sharing information on a public Facebook site and posting seismic records as far back as 50 years.

''My take is that there is a little swarm like this in Northland every 10 years or so,'' he said.

''There's no panic locally, there's quite a bit of joking about these ones. It's certainly a holiday conversation.''

However, Northland's off-shore earthquakes hardly made the Richter scale when it comes to being a notable event for the Crown agency GNS Science.

Northland is the least seismically active area in New Zealand, along with south east Otago, seismologist John Ristau said.

To put it into perspective, last year there were more than 19,500 seismic events recorded in New Zealand, with only 32 of those in the entire Auckland and Northland regions.

No place in New Zealand can escape the effect of the Australia and Pacific plates grinding together, which is the cause of the offshore ructions deep under the seabed. The North Island is on the Australia plate but Northland is nearer the boundary of the Pacific plate.

''Most of the earthquakes in New Zealand will occur close to these two main plates. Even though they're fairly rare in Northland, being part of New Zealand just means they're going to happen,'' Ristau said.

''Earthquakes like this [Whangārei cluster] are a good reminder to people that even in Northland we are never far from seismic activity.''

Regarding a possible tsunami, Ristau said the events were too far east, too deep and too small to even cause a ripple in the ocean.

As for why hundreds of people feel the earth move in quakes which are categorised as unnoticeable - the algorithms used in recording the data can't define the line between the source and effect.

The first of two earthquakes to shake and wake many around the district yesterday morning was categorised ''weak'', at magnitude 4.2, 12km deep, 55km east of Whangarei. The second was categorised as ''unnoticeable'', at a magnitude 1.9, 12km deep in the same location.