Don't lose any sleep over next big quake

Wellingtonians worried the city could be struck by a devastating earthquake at any time can sleep easier - scientists now think the city is not overdue for the "big one".

Mayor Kerry Prendergast will deliver the reassuring news today that it could be hundreds of years before the fault on which the city is built next ruptures in a major way.

That follows three years of research by scientists at GNS Science, the National Institute of Water and Atmospheric Research (Niwa) and Victoria and Canterbury Universities, in a project called It's Our Fault.

Project scientific leader Russ Van Dissen said the widespread perception that the city was overdue for a big quake was having a chilling effect on investment and the willingness of insurers to cover commercial property.

"It has a kind of ripple effect - one person says it's overdue, other people overhear it, they start being a bit more cautious about investments ... and it also has an impact on the ability to get insurance," said Mr Van Dissen, a seismologist at GNS Science.

That was one of the main reasons for the $3.5 million project, which is being funded by Wellington City Council, the Earthquake Commission and ACC.

The researchers, who have carried out more than a dozen studies as part of the project, aren't putting a date on when a magnitude 7.5 quake might hit, but say the chances are "significantly lower than previously thought".

They have three grounds for the more optimistic outlook. They now believe the last big quake on the Wellington fault was more recent than had been thought; that the gap between major quakes is hundreds of years longer than previously thought; and that an 8.2 magnitude shake on the nearby Wairarapa fault in 1855 took pressure off the Wellington fault.

"Those three things have all conspired in a positive way to say the Wellington fault shouldn't be regarded as being overdue [to go off]," said Mr Van Dissen.

But that does not mean a complete let-off, he said, because the fault remains active. It does suggest the city should prepare itself for more frequent quakes in the 6 to 7 magnitude range.

It's Our Fault is only halfway through. Mr Van Dissen said the project was a "roller coaster" in that the funders and scientists did not know where it would end up. The city can now take advantage of the discovery that disaster is not about to strike.