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Science paper on 'well behaved'Alpine fault
Science paper on 'well behaved'Alpine fault - experts
respond
28June 2012
New research out today
reveals that the Alpine Fault - a strike-slip fault running
almost the entire length of the South Island - is
surprisingly "well-behaved" in its regularity.
But good behaviour, in a scientific sense, may not bring much comfort to South Islanders.
In earthquake terms, the 850km-long fault is remarkably consistent, rupturing on average each 330 years, at intervals ranging from 140 years to 510 years.
The last major quake on the fault occurred 295 years ago, according to the GNS Science researchers who have compiled an 8000-year timeline of 24 major quakes on the fault from sediments at Hokuri Creek, near Lake McKerrow in north Fiordland.
Quoted in a press release for the paper, which is published today in the journal Science, the researchers including GNS principal scientist and manager of its Natural Hazards Research Platform Dr Kelvin Berryman, "calculate that there is a 30 percent chance a major earthquake will occur in Southern New Zealand sometime in the next 50 years".
Long earthquake records have been obtained from only about four other faults around the world, including the San Andreas Fault in California. The latest findings underpin an idea over 100 years old - that some faults might rupture regularly, rather than at random or in clusters.
The scientists say: "We propose that it is valid to apply time-dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide".
Other faults that have similar characteristics to the Alpine Fault include sections of the North Anatolian Fault in Turkey and the Denali Fault in Alaska.
The Science Media Centre contacted experts for their reaction to the research. Journalists registered with the SMC can log into the Resource Library to read the full paper, supporting material, and a Q&A from GNS Science.
NOTE: The comments below are abridged, see the SMC website for the comments in full.
Professor Richard Norris, Department of Geology, University of Otago, comments:
"It provides support for the view that the fault indeed ruptures at fairly regular intervals and has done so over several thousand years ... this is of international significance".
"The Alpine Fault has the highest level of probability for rupture of any fault in New Zealand".
"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). The fault crosses the west coast road in many places ... and with an estimated 8 m 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".
"Further east in the major cities of Christchurch and Dunedin, the intensities will be lower but the duration of shaking could still be sufficient to damage poorly constructed buildings ... and possibly cause some liquefaction".
"Places such as Nelson, Wellington and Invercargill could also expect to feel some shaking"
Dr Virginia Toy , Geology Department, University of Otago, comments:
"Rob Langridge of GNS Science has recently provided revised 'fault avoidance' maps to the Westland authorities based on LiDAR data around Franz Josef that was interpreted by an Otago postgraduate student, Nic Barth - scientists are continually working to help mitigate the effects of earthquakes".
Thomas Lumley, Professor of Biostatistics, University of Auckland, comments:
"The figure of 30% chance over the next 50 years looks plausible based on Figure 3B of the paper. The intervals between quakes tend to be quite close to the average interval, with relatively little spread".
"Looking at the graph, most of the recurrence intervals longer than 295 years (the position we are now in) are shorter than 400 years, and many of them are only slightly longer than 295 years.
"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. ... The risks are high, but that's because it seems to be an unusually regular fault".
ends
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