Geologists Shake Up Thinking On Earthquake Aftershocks
If you grew up in earthquake country, here's what you probably think you know about aftershocks: that they tend to happen soon after the big quake, and in the general vicinity. Well, scientists at the U.S. Geological Survey say that conventional wisdom is wrong.
The big revelation came earlier this year after a magnitude 8.6 quake shook the eastern Indian Ocean, off Sumatra. Almost immediately, Fred Pollitz with the USGS and other scientists noticed something that surprised them. "We saw within the first 24 hours four magnitude-six or greater earthquakes," says Pollitz. These aftershocks kept up for at least a week, as far away as Baja, California.
Pollitz says the discovery has forced a rethinking of how big quakes can trigger smaller ones in distant parts of the world. "There can be aftershocks at great distances, even up to 10,000 miles away ," says Pollitz. But he says scientists are a long way from being able to predict where such aftershocks will take place.