BBC News - Chile's long experience of quakes - 0 views
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It is not possible to predict the time and magnitude of an earthquake, but certain places on the Earth know they are always at risk from big tremors. Chile is one of those places.It lies on the "Ring of Fire", the line of frequent quakes and volcanic eruptions that circles virtually the entire Pacific rim. The magnitude 8.8 event that struck the country at 0634GMT on Saturday occurred at the boundary between the Nazca and South American tectonic plates, just off shore and at a depth of about 35km (20 miles).
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The Nazca plate, which makes up the Pacific Ocean floor in this region, is being pulled down and under the South American coast. It makes the region one of the most seismically active on the globe. Since 1973, there have been 13 events of magnitude 7.0 or greater.
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French and Chilean seismologists had recently completed a study looking at the way the land was moving in response to the strain building up as a result of the tectonic collision. Their analysis suggested the area was ripe for a big quake. "This earthquake fills in an identified seismic gap," Dr Roger Musson, who is the British Geological Survey's Head of Seismic Hazard, told BBC News.
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"The last major earthquake that occurred in this area was in 1835. This was a famous earthquake observed by Charles Darwin during his voyage on the Beagle. This is a place where the stress has been gathering for 170 years, and finally it's gone in another earthquake that's repeated this famous historical quake." As is nearly always the case, the region was hit by a series of aftershocks. In the two and a half hours following the 90-second 8.8 event, the US Geological Survey reported 11 aftershocks, of which five measured 6.0 or above.
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Saturday's quake was almost 1,000 times more powerful than the one to hit Port-au-Prince in Haiti. But size is not in itself an indicator of the likely number of deaths. One major factor which will limit the number of deaths in Chile will be its greater level of preparedness. Both the Chilean authorities and the Chilean people are generally well versed in how to cope in such an emergency.
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The emergency response system is organised at national, regional and local level. "Chile is a seismic country. So, we must be prepared!" is the message from Onemi.