20100301 Chile's long experience of quakes (1)

clipped from news.bbc.co.uk 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). The biggest city close by is Concepcion, just over 100km to the south. Because the quake occurred below the sea floor, tsunamis were also generated, and alerts were issued not just for the Chilean coast but across the Pacific in general. The Nazca and South American tectonic plates are vast slabs of the Earth's surface and grind past each other at a rate of about 80mm per year. It makes the region one of the most seismically active on the globe.