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Friday, March 4, 2011

No big Wellington quake coming - seismologist

No big Wellington quake coming - seismologist

Last updated 12:12 04/03/2011
Two earthquakes that rattled Wellington this week are no indication that a deadly Christchurch-scale disaster is set to hit the capital in the near future, a seismologist says.

Many Wellingtonians were shaken from their sleep early this morning when a magnitude 4.7 quake struck at 2.19am. It was centred 10km northeast of Upper Hutt, at a depth of 30km. Police said there were no reports of damage.

This morning's tremor followed a magnitude 4.5 quake on Tuesday.

GNS Science duty seismologist Dr John Ristau said there was no connection between the two Wellington quakes and the recent flurry of seismic activity in Christchurch.

"They really have nothing to do with what's going on in Christchurch, these couple of earthquakes here in Wellington. They're really nothing unusual," he said.

Ristau said Wellington could expect three or four quakes of a similar magnitude and depth every year.

"It's just a bit of a coincidence, I guess, that we had two in the last few days, and that they happened a week after the 6.3 in Canterbury," he said.

"It's not to say that an event like that couldn't happen in Wellington - in fact one day it will. But these couple of earthquakes that we've had in Wellington, they're not any indication that there's anything bigger coming for Wellington in the near future."

Ristau said that Wellington was generally "much more seismically active than the Canterbury region", due to several major faults, most notably the Wellington fault.

"Beneath Wellington you have the Pacific tectonic plate that's pushing beneath the Australian tectonic plate, which the North Island is sitting on. And both these earthquakes happened inside of the Pacific plate, as it's pushing down beneath Wellington.

"The tectonic situation for what's going on in Canterbury is completely different."

However, that did not mean Wellingtonians could be complacent.

"One day there will be a Canterbury-size earthquake in Wellington, or even bigger than that."

Dr Risatu said it was impossible to predict when the next big one would strike the capital.

"All we can do is basically look through the past historical and geological record. We know that the faults exist, we know that the earthquakes do happen, and we can figure out on average how often they happen and when the last one was. But that's about the best we can do."

A major earthquake was expected once every 700 years, and Wellington was about halfway through that cycle, he said.

This morning's quake comes after Wellington City Council yesterday released a list of 808 potentially earthquake prone buildings spread across 217 of the capital's streets.

The list shows street names and numbers, but buildings are not named.

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