Friday, 16 August 2013

What can Wellington expect in terms of a big earthquake?

Dozens of aftershocks have rattled central New Zealand overnight following yesterday's 6.6 quake, as Wellington gets back to business and Seddon, where most of the quakes were centred, starts its clean up.
There have been 44 quakes over magnitude 4.0 since yesterday's 6.6-magnitude quake, said GeoNet.
It has caused widespread damage in Seddon and Marlborough and sparked traffic chaos in Wellington as workers tried to leave the central city en masse.
The elevator shaft in Lukes Lane.
The elevator shaft in Lukes Lane.
A nine storey lift tower in Lukes Lane in Wellington, which had already been damaged in the earthquake on 21 July, suffered further damage on Friday and residents in neighbouring properties were evacuated on Friday afternoon.
So what realistically can Wellington and the rest of New Zealand that sits on a major faultline, expect? This article and excellent graphic explsins that we could get another destructive Magnitude 8 earthquake in the next 30-40 years. In geological terms, that could mean tomorrow.

June 28, 2012 – NEW ZEALAND – GNS Science and University of Nevada-Renoscientists have found that the southern part of the 800 kilometre-long fault which runs along the western edge of the Southern Alps from Marlborough to Milford Sound causes quakes of around magnitude 8 every 330 years on average. Dating leaves and seeds from a river terrace at Hokuri Creek near Lake McKerrow in far northwestern Southland, just north of Milford Sound, revealed 24 Alpine Fault quakes between 6000BC and the present. Other research has found the most recent was in 1717, meaning the next may be only 30 or 40 years away, based on averages. Professor Richard Norris, from the geology department at Otago University, said the Alpine Fault had 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 (as well as the tourist trade),” he said. The fault crossed the main West Coast road in many places, and with an estimated 8m displacement would 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,” Norris said. “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. Project leader Kelvin Berryman of GNS Science said “a major earthquake in the near future would not be a surprise. Equally it could be up to 100 years away. The bottom line is, if not in our lifetimes then increasingly likely in our children’s or our grandchildren’s.” The study’s findings, published today in the journal Science, were new and internationally significant, Berryman said. Auckland University biostatics professor Thomas Lumley said the intervals between quakes on the Alpine Fault tended to be quite close to the average interval, with relatively little spread. –Stuff

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