'Major' quake due on Alpine Fault
Thu, 28 Jun 2012 12:59p.m.
By Dan Satherley
There is a 30 percent chance of a "major" earthquake occurring on the Alpine Fault in the next half-century, geologists have warned.
The fault, which runs almost the entire length of the South Island, ruptures with "well-behaved" regularity, according to research published this week in the journal Science.
Quakes with an approximate magnitude between 7.6 and 8.3 occur on average every 329 years, GNS Science researchers using radiocarbon dating have found.
Between 6000 BCE and today, evidence was found for 24 separate quakes on the Alpine Fault. It has been about 295 years since the last shake, increasing the likelihood it is due for another.
"The Alpine Fault has the highest level of probability for rupture of any fault in New Zealand," says Professor Richard Norris of the Department of Geology at the University of Otago.
"Most of the recurrence intervals longer than 295 years are shorter than 400 years, and many of them are only slightly longer than 295 years," says Thomas Lumley, Professor of Biostatistics at the University of Auckland.
"That is, most of the time when a quake hasn't happened for 295 years, it happens within the next century and often within the next half-century."
Each year the fault shifts around 14mm in the north and 31mm a year in the south, making it responsible for two-thirds of the relative motion between the Pacific and Australian plates.
The last quake however is estimated to have shifted land around 1m vertically and 7.5m horizontally.
A magnitude 8 quake would release around 31 times more energy than the September 4, 2010 quake in Canterbury, and around 350 times stronger than the February 2011 event.
"Westland obviously is at high risk, with widespread damage likely and roads, bridges and other transport links likely to be badly affected (and the tourist trade)," says Prof Norris.
"The fault crosses the West Coast Road in many places, and with an estimated 8m displacement, will completely destroy it.
"Intensities further east in places like Queenstown, Te Anau, Wanaka and Mt Cook will be high enough to cause landslips and do damage".
It would even be felt as far away as Nelson and Wellington.
This morning the Ministry of Civil Defence and Emergency Management announced it will be conducting a nationwide earthquake drill later this year, due to incorrect reports on what to do when one strikes.
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3/07/2012 11:37:17 p.m.
Because its been happening since the beginning of earth. Some areas like fiordland show good records of the large ones. We just need to be prepared for it.
28/06/2012 6:17:38 p.m.
rachel pero wrote:
how hard would it hit christchurch and will it cause us much damage and many deaths. how can people predict these things?
28/06/2012 6:17:35 p.m.
28/06/2012 5:55:35 p.m.
They're only assuming that based on the most recent ruptures, and assuming that the trend continues. It may not. They don't know. This isn't news, it has been said over and over and still nobody knows for certain when it will happen. It could be another 100 years.
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