Southern Ocean quake sparks tsunami fear

A large earthquake in the Southern Ocean initially prompted fears of a tsunami.

The 7.4 magnitude quake yesterday was felt in Stewart Island and Invercargill, and as far north as Dunedin.

It hit at 6.23pm near the Auckland Islands, about 470 kilometres southwest of Bluff and 1240km southwest of Wellington. It prompted an immediate bulletin from the Pacific Tsunami Warning Centre in Honolulu, which warned that the quake could generate a tsunami within 100 kilometres of its epicentre.

The centre alerted the Civil Defence Ministry, whichadvised the Otago and Southland Civil Defence Emergency Management groups. "That's a sizeable earthquake," oceanologist Nathan Becker said in Honolulu. "But fortunately it was away from highly populated areas." Oceanologists would monitor tide gauges for evidence of a tsunami, he said.

A GNS Science-convened tsunami expert panel and Niwa scientists also monitored and assessed information about the quake and sea level movements.

GNS senior seismologist Warwick Smith said people in the south of the South Island reported feeling a long rolling motion.

"That is what you would expect from a very large earthquake a very long way away. It's a very big earthquake."

It was fortunate that it happened so far out to sea, and in an area not conducive to tsunamis. Earthquakes in the Southern Ocean tended to be horizontal, rather than vertical.

"If this had happened on land, particularly near a city, you would be looking at a lot of damage," he said.

In 2003, a 7.3-magnitude quake was recorded west of Te Anau, and in 1991 a similar sized one was measured near East Cape.

Two earthquakes came within a minute of each other near Matata early yesterday. They were felt across Bay of Plenty.

GNS Science first reported an earthquake measuring 4.7 at 1.12am, centred 10km northeast of the township at a depth of two kilometres. Later it said there had been a second earthquake, measuring 4.5, at the same location one minute later.