Swarm of strong aftershocks expected says geologist

11.40am

South Island residents can expect a swarm of strong aftershocks over the next two to four days, Dunedin-based GNS geologist Simon Cox said.

An earthquake measuring 7.2 on the Richter scale struck off the coast of the South Island today.

Dr Cox, who was in the initial GNS response team to visit Fiordland after a 7.2 quake in August 2003, said that based on the aftermath of that quake, a second strong quake may hit the South Island within hours of the first.

"After the Fiordland quake there was a magnitude 6.5 two hours afterwards, which was certainly felt around the South Island as far (north) as Christchurch," Dr Cox said.

"After a magnitude 7.2 you will always expect aftershocks."

It was impossible to predict exactly where the aftershocks would be felt after today's quake, but an "active swarm" of them would probably be felt widely across the South Island.

The normal sequence would be for them to decrease in magnitude but continue for the next few days at the same frequency, he said.

Today's quake was felt widely throughout the South Island, and in the North Island as far north as New Plymouth which was on the same fault line.

The quake hit at 9.26am 240 km southwest of Te Anau, at a depth of 33km. The GNS had received no reports of damage this morning.

- NZPA