Giant Earthquake Predictions Aided by Historical Data

Stefan Lovgren
for National Geographic News
September 15, 2005

Predicting when the next giant earthquake will occur is a shaky proposition. But new analysis of an unusual seismic fault in Chile could help scientists better understand when and where giant earthquakes are likely to recur.

Geologists believe that the longer a seismic system goes without experiencing an earthquake, the more strain it accumulates and the larger the next quake will be.

This theory applies only to so-called subduction zones, where one tectonic plate moves over or under another. Strike-slip faults, where plates grind against each other, store stress differently.

But the behavior of a seismic fault in a subduction zone in Chile has confounded seismologists' predictions.

A 9.5 magnitude earthquake—the biggest ever recorded—rocked that region in 1960. The energy released should have taken several centuries to build up. But the area also experienced earthquakes in 1837 and 1737.

A new study shows that the earlier quakes probably did not release much of the stress building on the fault. Instead, strain kept accumulating on the fault ever since a large quake occurred there in 1575.

The findings are reported today in the science journal Nature.

"It [would be] very difficult to expect a very large earthquake along a portion of a fault that has recently been ruptured," said Sergio Barrentos, a scientist at the Comprehensive Nuclear-Test-Ban Treaty Organization in Vienna, Austria.

Barrentos, who was not involved with the research, wrote a commentary published with the study.

Giant Tsunami

The 1960 earthquake in Chile resulted from a rupture along a fault where one tectonic plate slides under another at the west coast of South America. The break was about 620 miles (1,000 kilometers) long and 93 miles (150 kilometers) wide.

The monster quake produced a giant tsunami on both sides of the Pacific Ocean, with crests as high as 30 to 50 feet (10 to 15 meters) in Chile and 20 feet (6 meters) in Japan.

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