New Zealand earthquake caused by new fault line
Wednesday 23 February 2011
The devastating earthquake that tore through Christchurch on Tuesday is the product of a new fault line in the Earth’s crust that seismologists were previously unaware of.
New Zealanders have long known that their mountainous country is acutely vulnerable to tectonic movements. Major fault lines dissect the nation, snaking up the western coast of the South Island before splitting in two just south of the capital Wellington.
For those charged with the unenviable task of trying to predict where the next major quake would strike it was always Wellington that created the most concern thanks to a prominent fault that is expected to produce a major earthquake in the next few decades and runs directly through the city centre.
In comparison seismologists were more relaxed about Christchurch which – until six months ago – was thought to lie more than 80 miles away from the nearest known fault line.
"Wellington has always been considered much more at risk because it straddles the plate boundary,” explained Australian Seismological Centre director Kevin McCue
But the two major earthquakes and hundreds of aftershocks that have battered Christchurch in the space of five months have turned such thinking on its head. Instead seismologists believe that a brand new fault, one which might have lain dormant for thousands of years, has sprung back into life with devastating consequences.
“It’s not a new fault in the sense that it has only just been created but it is a new fault that has only just been discovered,” Dr Roger Musson, head of seismic hazards and archives at the British Geological Society, told The Independent. “Some fault lines are very easy to see but the one under Christchurch is covered by sediment and would have been invisible without thorough geophysical searches.”
Since the first quake in September, which was stronger than Tuesday’s but did less damage, geologists have been desperately trying to map the new fault which is thought to branch out from the main line running up the west coast of the South Island and run under the plain on which Christchurch has been built.
Although predicting precisely where an earthquake will strike at a what intensity remains all but impossible, effective mapping and monitoring of fault lines allows scientists and city planners to make better judgement calls on how much time or resources should be spent on shoring up a major city against future quakes.
Mapping also provides a frightening window into the future. Most seismologists are now convinced that major earthquakes are all but inevitable over the next century in places as densely populated as Istanbul, Los Angeles, Tehran, Karachi, Kathmandu and Lima, all of which have active fault lines running through or close to them.
Istanbul in particular is a terrifying prospect. In August 1999 an earthquake on a previously quiet fault tore through the city of Izmit killing 18,000 people. Since then smaller quakes have erupted with regularity across the fault, heading west towards Turkey’s largest city, a sprawling metropolis of 13m people.
In Iran some geologists have even petitioned the government to have the capital moved from Tehran, which has a fault line running under its biggest hospital, to the city of Qom. Turkish researchers have suggested that if an earthquake of the same intensity that hit Haiti in January 2010 struck Tehran up to one million could perish.
Cities like Christchurch, which are only known to lie on a fault once an earthquake occurs, are much harder to protect against. Recent seismological studies have suggested that major cities like New York and Beijing, which are situated far from tectonic plate boundaries, may in fact be more vulnerable than previously thought to seismic shifts.
New Zealand will now understandably be keen make sure that any rebuilding of Christchurch is of a quality that can withstand similar quakes. But mother nature is difficult to predict and few can say for sure whether the new fault running under the city will continue to cause catastrophes or return to its dormant states.
“This particular fault has probably been still or inactive for the past 10,000 years and we may find that after this burst of activity it will return to an inactive state for another 10,000 years,2 explains Dr Musson. “The difficultly of disaster management is that, like military planning, you often find yourself using the previous war to prepare for fighting the next one.”
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