Quakes not sign of 'big one', say seismologists

By SIMON COLLINS, science reporter

Seismologists believe the swarm of small earthquakes which added to the Bay of Plenty's misery is not a sign of "a big one" to come.

Dr Warwick Smith of the Institute of Geological and Nuclear Sciences said earthquake swarms were common in the central North Island volcanic zone.

Sunday's swarm was bigger than usual, with a maximum shake of 5.4 on the Richter scale at 4.22pm and another of magnitude 5 at 6.40pm. New Zealand usually gets only three or four shakes of 5.4 or bigger each year.

The biggest quake was centred a few kilometres north of Lakes Rotoehu and Rotoma, on the edge of the large Okataina volcanic crater which contains the Rotorua lakes and last blew in the devastating Tarawera eruption of 1886.

But Dr Smith said there was no indication that a volcano was about to blow again. "These earthquakes do occur throughout that area and we don't get volcanoes blowing all the time," he said.

"We really don't know, but our judgment is that this is the sort of thing that we see from time to time and it will cool off within a day or so. We may be wrong, but we have to exercise our judgment."

He said there was no reason to believe that there was any connection between bad weather and earthquakes, which were driven by events deep inside the Earth. New Zealand's worst quake, the Napier shake in 1931 which measured 7.8 on the Richter scale and killed 256 people, occurred on a brilliantly fine February day.

He also questioned reports that an earthquake toppled a tree which fell on a car and killed the occupant on Pyes Pa Rd near Tauranga at about 4pm on Sunday. The site was a long way from the epicentre of the biggest shake, and that shake occurred at 4.22pm, not 4pm.

"So maybe it was not the earthquake that caused it," Dr Smith said.

Recent quakes