Little quakes a big shock

Few Aucklanders noticed an earthquake "cluster" directly beneath Waiheke Island but the event was rare enough to make scientists sit up.

Two small shakes, measuring 2.5 on the Richter scale, were felt on Tuesday night. Another shake, measuring 3.3, followed yesterday. Three other ones in the same time frame were too small to be felt.

GNS Science (formerly Geological and Nuclear Sciences Ltd) seismologist Dr Ken Gledhill said the event was relatively rare. "There have been earthquakes under the Hauraki Gulf before but it was most unusual for three to occur in one day," he said.

There was no known fault where the earthquakes occurred. But it was unlikely the quakes, about 8km deep, were a signal Auckland's volcanic field was reawakening.

"The most likely explanation is that there is a knot of tension in the earth's crust which is gradually being relieved," he said. "There could be more earthquakes in this sequence."

Waiheke resident John Hawkesby said he felt a slight motion of his car and instinctively looked towards the nearest volcano. "I have a good view of Rangitoto from here and I thought after all these years she's going to blow and I'm in the box seat."

Waiheke accountant Bev Bourke was at home in Blackpool, on the island's western coast, when her daughter noticed the shake.

"I'm from Taranaki so I knew immediately it was an earthquake," she said.

Auckland has fewer earthquakes than other areas as it does not sit directly above the faultline where the Pacific and Australian tectonic plates collide.

Mr Hawkesby wasn't taking chances. "I'll open a nice bottle of wine tonight, just in case it's my last. If this is it, I want to go out in style."