Fault 'well-behaved' but big quake closer
NZ Newswire
June 28, 2012, 3:10 pm
Scientists studying the faultline that runs along the
Southern Alps have gone back thousands of years further than previous
studies and discovered it is "well behaved" and something of a creature
of habit.
But they warn the new information leads them to believe
there is a 30 per cent chance of a destructive magnitude 8 earthquake
within the next 50 years.
Scientists had previously only known the ages for four large Alpine Fault quakes dating back to about 1000AD.
In
Science magazine this week, GNS Science, with help from Victoria
University of Wellington, as well as scientists from Italy, Israel, and
the US, revealed the fruits of their four-year research project.
Focussed
on a remote river terrace near Milford Sound, they used radiocarbon
dating of seeds, leaves, and reeds contained in swampy sediments, to
determine the ages of 24 surface ruptures, of about magnitude 8, dating
back to 6000BC.
The findings dramatically improve the known
earthquake history of the 600km-long fault which runs up the spine of
the South Island.
The mean interval between large earthquakes on
the fault is 330 years and two thirds of the intervals were between 260
and 400 years. The fault last ruptured in 1717.
"On a national
scale, we can now base our modelling on knowledge of the timing of 24
earthquakes compared to the four that were known prior to this
investigation," said project co-leader Kelvin Berryman, of GNS Science.
"This will greatly improve the reliability of earthquake hazard modelling."
University
of Otago geologist Richard Norris said a magnitude 8 quake could cause
widespread damage in Westland, landslides and damage in places like
Queenstown, Te Anau, Wanaka and Mt Cook.
In Christchurch and
Dunedin the intensities will be lower but could damage poorly
constructed buildings and possibly cause some liquefaction.
Places such as Nelson, Wellington and Invercargill could also expect to feel some shaking.
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