All shook up. Seismic waves from the large earthquake outside Sumatra triggered smaller quakes around Mount Wrangell in Alaska.

The Quake That Shook the World

Studies of the large Sumatran earthquake that caused the devastating tsunami in December have shown for the first time that earthquakes can trigger smaller quakes as far away as the other side of the world.

On 26 December, an earthquake measuring 9.1 on the Richter scale hit off the Indonesian island of Sumatra, triggering a tsunami that killed nearly 300,000 people. Researchers knew that such large quakes might spark seismic events far away, but just how large and distant these events could be was unknown.

Now, seismologists led by Michael West of the University of Alaska, Fairbanks, have shown that 14 small earthquakes near Alaska's Mount Wrangell--nearly 11,000 kilometers from Indonesia--were related to the Sumatran quake. A network of seismometers around the volcano indicated that the ground started shaking about an hour after the Sumatran quake--due to surface waves traveling along Earth's crust. In addition, the Alaskan quakes occurred systematically every 20 to 30 seconds in sync with the waves from Sumatra, the researchers report today in Science. "We now know that earthquake triggering is a truly global phenomenon," says West. "A great earthquake such as [the one that hit] Sumatra can trigger seismic activity anywhere on Earth."

Joan Gomberg, an earthquake seismologist at the U.S. Geological Survey in Memphis, Tennessee, says that these kinds of observations may give seismologists clues to how other regions of the world may be affected by long-distance seismic events.

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