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Big quakes not outside global trend - 22/09/1999

The recent series of big overseas earthquakes in populated areas is nothing out of the ordinary in terms of size and frequency of large quakes around the world, the Institute of Geological & Nuclear Sciences Limited (GNS) said today.

Large earthquakes happen regularly, but there has been a run of populated areas being hit, GNS seismologist Terry Webb said.

" This has led to the false impression that there has been an increase in global earthquake activity," Dr Webb.

" Big earthquakes occur regularly with many occurring under the ocean or in sparsely populated areas. If they don’t cause damage they don’t register in the public consciousness."

Global earthquake statistics for the past 20 years showed there was a relatively steady occurrence of big quakes. Recent large earthquakes in Turkey, Greece, and Taiwan were not out of place in a global sense.

Dr Webb said there was no scientific evidence to support suggestions that a big quake in New Zealand could be triggered by this week’s magnitude 7.6 quake in Taipei.

" Stress triggering – where one big shock can set up another – does occur but only over relatively short distances, up to 150 kilometres."

" There’s no clear evidence that stress triggering can happen over much larger distances."

Records showed that, on average, New Zealand could expect one shallow quake of magnitude 6 or greater every year, one magnitude 7 every 10 years, and an 8 every 100 years.

" New Zealand has been relatively quiet in recent decades with the magnitude 6.5 Edgecumbe earthquake in 1987 the only significantly damaging on-land shock in the past 30 years.

" If a shallow magnitude 6 quake hit a population centre, it could cause severe damage. A magnitude 7 - 30 times more powerful than a magnitude 6 - could be very destructive if it hit a New Zealand city.

" It’s inevitable that sometime in the future a quake of similar magnitude to those in Taiwan and Turkey will strike a populated area in New Zealand.

" Since there’s no way of forecasting when this will happen, it pays to be sensibly prepared."

Dr Webb said there were many similarities between preparing for a big quake and preparing for the Y2K bug.

" People have been urged to prepare for Y2K, but it makes sense to be prepared in this way all the time.

" Evidence from the big overseas quakes is that a good level of disaster preparedness can pay huge dividends both on an individual level and for the whole community."