Australia wary of NZ quake

A New Zealand seismologist last night dismissed claims by a New South Wales tsunami expert that an earthquake similar in scale to the south Asian disaster was due on a major New Zealand faultline.

Professor Ted Bryant, from the University of Wollongong, said the South Island's alpine fault caused an earthquake every 500 years and the last quake was about 500 years ago.

Professor Bryant said it was the closest faultline to Australia and Sydney could be threatened by an earthquake there.

"When it goes it will generate an earthquake over eight on the Richter scale," Professor Bryant told Seven's Sunrise programme.

"If it goes over the ocean, if the epicentre is under the ocean, then that will generate a tsunami."

But Dr Warwick Smith, of the Institute of Geological and Nuclear Sciences, said it was misinformed to say an earthquake was due.

Dr Smith said the institute estimated an earthquake on the South Island alpine fault every 300 years on average, not every 300 years on schedule. In 3000 years there would be about 10 earthquakes irregularly spaced, he said.

"It hasn't happened in historical times. It doesn't mean it's due. It just means it is going to happen sometime.

"The other thing is the alpine fault is mostly on land. What it takes for a tsunami is an uplift or subsidence of the ocean floor. It is difficult to see how an alpine fault earthquake would do the same sort of thing as this huge 1000km long source that ruptured off Sumatra.

"It is true the alpine fault does extend offshore down past Milford Sound but no way are you talking about the scale of event as we have seen in Indonesia and up around the Indian Ocean."

Professor Bryant said a tsunami generated by the alpine fault would take up to three hours to cross the Tasman Sea.

Sydney's cliffs would not necessarily protect the city from a tsunami, with the massive wave of water swelling above the 80m rock faces.

- Staff reporter/AAP