Auckland at risk from unseen threat

Photo / NZ Herald

Could Auckland be next? Scientists say the Christchurch quake was a good reminder that all of New Zealand lay near a major intersection of tectonic plates.

The risk of a major tremor is unlikely above the Waikato. But the discovery of a "blind" or long-buried faultline near Darfield emphasised the existence of latent dangers deep in New Zealand's earth.

Associate Professor Phil Shane from the University of Auckland geology department said Wellington remained the city most at risk.

"The other side of the coin is that all of New Zealand is on a plate boundary, so most of New Zealand has experienced seismic activity in its history," he said.

"The Canterbury situation is a reminder that some of the older faults are buried. It leaves the door open to places even further north, like the Waikato, experiencing movement occasionally."

The closest faults to Auckland lay south of the city, near the Hunua Ranges. They were not believed to have moved, or ruptured the surface, in the past 1000 years.

Professor Shane said because many of the major cities were built on soft rock or sediment, a quake which occurred outside city centres could still be highly damaging.

Low-lying and coastal areas in Auckland, such as the waterfront, would be badly damaged by a large tremor, as the land could liquefy, shaking much of downtown's foundations.

The most likely region to experience a major quake in the North Island was the Bay of Plenty, he said.