Chile's record quake


		Northwest Geology News Four centuries of stress led to Chile's record quake

Reprinted with permission of The Oregonian
Wednesday, September 21, 2005

Four centuries of stress led to Chile's record quake

A lethal magnitude 9.5 earthquake that rocked Chile in 1960 -- the largest quake ever recorded -- was preceded by nearly 400 years of accumulating stress, a study shows. Strain had been building since the Spanish conquistadors were jolted by a large quake in 1575. Seismologists had been puzzled because the region had had earthquakes in 1837 and 1737, so the offshore fault would not have had time to build enough stress to produce the 1960 monster.

A team led by Chilean researcher Marco Cisternas studied 2,000 years of soil and sand deposits. The researchers found that the two quakes probably did not significantly release the stress building on the fault.
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The 1960 quake, which launched a tsunami that caused most of 5,000 deaths, occurred on a subduction zone where the Nazca and South American plates converge offshore. It is geologically similar to the Cascadia Subduction Zone off the Northwest coast, which evidence indicates has produced several magnitude 9 quakes, the most recent one in 1700. A subduction zone off Sumatra triggered the deadly magnitude 9 quake and tsunami in December.

The researchers included Seattle scientists Brian Atwater of the U.S. Geological Survey and Annaliese Eipert of the National Oceanic and Atmospheric Administration. They reported their findings in the current issue of Nature.

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Northwest Geology News Four centuries of stress led to Chile's record quake

Northwest Geology News
Four centuries of stress led to Chile's record quake