Spate of quakes recorded around Cook Strait

A series of light quakes have been recorded in the Cook Strait area over the last 24 hours. Image / GeoNet

A series of light quakes have been recorded in the Cook Strait area over the last 24 hours.

Many Wellingtonians reported feeling a magnitude 3.8 quake that struck about 30km southwest of the capital, at a depth of 13km, just after 7pm last night.

Within an hour came a pair of magnitude 3.3 quakes that hit 35km southwest of Wellington.

This afternoon, GeoNet instruments registered two quakes, measuring 4.1 and 3.2, located around 20km south-east of Seddon.

GNS Science duty seismologist Jon Ristau said it was unclear whether the events were just more of thousands of quakes that have been recorded in the aftermath of the 7.8 Kaikoura quake, or if it was typical background behaviour for the region.

Ristau said the Cook Strait is well known to be a seismically active area - as dramatically demonstrated by 2013's Lake Grassmere and Seddon earthquakes.

There was also nothing to suggest the quakes were part of an emerging swarm.

"Usually, when you think of a swarm of quakes, they're all clustered or bunched together, whereas these were all a little more spread out."

GeoNet had, however, observed a weekend swarm around the coastal Hawke's Bay town of Porangahau.

More than 30 small quakes - most too weak to be felt - had been recorded there following a magnitude 3 quake last Friday night.

The area had been seismically active over the past decade, GeoNet public information specialist Sara Page wrote in a blog post.

"We have learned that this is an area that is very sensitive to changing conditions that happen whenever the ground shakes or moves."

Whenever it experienced the effects of a strong regional earthquake, such as the Kaikoura quake, or local "slow slip" quakes, the area responded by generating swarms of relatively small earthquakes.

"Exactly why this region appears to behave a bit differently than others around it is still a mystery, but one that is keeping GNS Science seismologists busy looking for an answer," Page said.

"Perhaps solving this question will leave us better able to forecast large subduction earthquakes that might impact New Zealand in the future."