GEONET

An image from Geonet showing clusters of quakes near Blenheim and Seddon.

A series of 15 earthquakes have been shaking the region from Kaikōura to the Cook Strait since the start of the weekend.

The four strongest, all Magnitude 4 or higher, have clustered around Seddon - and the residents have certainly noticed.

They're most likely all aftershocks from the November 2016 Kaikōura earthquake.

Marlene Jackson, who works at the Cozy Corner Cafe and Bar on the side of State Highway 1 in Seddon, said: "We're feeling them all right.

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"It shakes you up because it feels like it's going to keep going ... it shakes all your windows and rattles all your plates and just gets you thinking if it's going to be another big one."

The quakes had just started up again, she said.

"We had quite a few over the weekend. We had little ones we wouldn't have felt but these fours we're feeling."

She agreed when asked if it was an unpleasant reminder of the Kaikoura quake for those in the town.

GNS Science seismologist John Ristau said: "We would consider these aftershocks from Kaikōura. But one thing to keep in mind is the whole area along the northeast coast of the South Island and out in the Cook Strait - that's always a fairly seismically active area anyway."

"One thing of course is that all aftershocks are earthquakes ... probably the best way to think of it is to think of Canterbury instead of Kaikōura. 

"Canterbury, prior to September 2010, the 7.1, that whole area - for New Zealand - was quite seismically quiet.

"Then of course the Darfield earthquake happened and you have thousands and thousands of earthquakes going on ... once things sort of get back to that same sort of level we were before [a big quake], we would consider them not to be aftershocks anymore."

Generally, the bigger the quake, the longer it took for aftershocks to die down.

"If you think about Canterbury, it's still quite a bit more seismically active than it was before the Darfield earthquake and now we're going on almost eight years."

Despite that, it was possible to get large earthquakes that didn't produce aftershocks.

The Kaikōura quake hadn't been as active in generating aftershocks as expected, Ristau said.

SCOTT HAMMOND/STUFF

A damaged wall in Seddon following the Kaikōura earthquake. The town is still feeling aftershocks, more than a year and a half later.

Getting to a pre-November 2016 frequency of quakes could take years.

"Probably five years - 10 years from the time the earthquake happened,"  Ristau said.

"But also, one thing to consider is ... in July and August 2013, right around the same area we had the two 6.5 earthquakes, so there's no reason to think somewhere in this area in two or three years there couldn't be another 6.5 that's unrelated to Kaikōura - just a 6.5 on its own - and that one generates its own whole series of aftershocks, and that continues.

"In some respects, you can say it'll never stop."

Often, aftershocks were clustered together in time.

"It's likely, what would have happened was ... there was a bit of stress built up at this point and it's all going pop."

"The most likely scenario is that this will all quite down in the next few days."

M3 to M4 aftershocks for "years afterwards" were common for quakes the size of Kaikōura, Ristau said.

SCOTT HAMMOND/STUFF

Damage from the November 2016 Kaikōura earthquake at the Seddon Supervalue.

 - Stuff