Risk of new Chile quake seen after 2010 disaster

OSLO Sun Jan 30, 2011 1:03pm EST

A girl sits among the debris left by a major earthquake and ensuing tsunami in Llolleo, March 3, 2010. REUTERS/Eliseo Fernandez

A girl sits among the debris left by a major earthquake and ensuing tsunami in Llolleo, March 3, 2010.

Credit: Reuters/Eliseo Fernandez

OSLO (Reuters) - The risk of a new earthquake may have increased in an area of Chile's Pacific coast that suffered a massive quake and tsunamis last year that killed more than 500 people, a team of scientists said on Sunday.

They said the 8.8 magnitude February 27 quake had only partly broken stresses, deep in the Earth's crust in an area south of Santiago, that have been building up since an 1835 quake witnessed by British naturalist Charles Darwin.

"We conclude that increased stress on the unbroken patch may in turn have increased the probability of another major to great earthquake there in the near future," they wrote in the journal Nature Geoscience.

A "major" earthquake is between magnitude 7 and 8, causing serious damage over large areas, and a "great" earthquake above 8. Chile's quake was the most powerful since the 2004 quake that caused a devastating tsunami in the Indian Ocean.

"It's impossible to predict exactly when a new quake might happen," Stefano Lorito, of Italy's Istituto Nazionale di Geofisica e Vulcanologia, told Reuters. He led a team of experts in the United States, Northern Ireland and Italy.

The scientists examined data from tsunamis, satellites and other sources to judge the risks in an area they called the "Darwin gap" on the coast around the city of Concepcion.

Darwin, on a five-year voyage that helped him unlock understanding of evolution, documented the 1835 earthquake that battered an area of the coast around Concepcion.

They found that a continental plate beneath the Pacific Ocean was sliding under the South American mainland at a rate of about 6.8 cms (2.7 inches) a year, so that a total of almost 12 meters (39 ft 4.4 in) of streses had built up since 1835.

When pressures build up enough, they snap and cause a quake. Some areas, deep below ground to the north of Concepcion, slipped almost 20 metres in the 2010 earthquake but the area of the "Darwin gap" barely moved.

Darwin made detailed observations, from the destruction of Concepcion cathedral to rotting mussel beds found on rocks raised by the jolt to 10 feet above the high tide mark. Other quakes have hit the region in 1928, 1939, 1960 and 1985.

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