A series of mainly unnoticeable earthquakes continuing off the Northern Hawke's Bay coast since a significant 5.4 magnitude shake a week ago is not unusual, according to a leading seismologist.

John Ristau, of national research institute GNS Science, was speaking as the swarm in the area about 30km east of Wairoa, where the bigger quake was recorded at 6.16pm on October 1, the first in a swarm that has risen to over 70 in seven days.

There had also been a considerable number of other quakes north and south of the area, including several east of Hastings, the biggest also at 3.5 magnitude.

Ristau said the public perception that the swarm as a settling down process was correct.


"The east coast is one of the more seismically active areas, and you do get certain hot-spots," he said.

"They are what we call normal faulting. There hasn't been too much analysis of it yet, but a large number aftershocks could have been expected for an earthquake of that size (the October 1 shake)."

He said it tended to be the bigger the quake, the more tremors that followed.

"There's nothing unusual about it," he said.