for National Geographic News
Even as the death and destruction toll from the tsunami that struck much of Southeast Asia a week ago continues to mount, attention is also focusing on the Pacific Ocean.
Scientists say that huge tsunamis are much more likely to develop in the Pacific Ocean than in the Indian Ocean.
That's because the Pacific Ocean has many more subduction zones, which produce the most powerful earthquakes and tsunamis.
Knowing the danger, Pacific Ocean countries have set up a sophisticated warning system. They hope the system will keep the death toll from a potential giant tsunami far lower in the Pacific Ocean than it was in the Indian Ocean, where at least 140,000 people were killed by the recent tsunami.
Residents along North America's Pacific coast would have very little time to get to higher ground.
"If a magnitude 9 earthquake were to strike in the Pacific Northwest and generate a tsunami, we'd have less than 15 minutes warning [before it hit the shore]," said Robert Yeats, a professor emeritus of geosciences at Oregon State University in Corvallis.
A tsunami is a series of great sea waves. While tsunamis can be triggered by landslides or volcanic eruptions, most tsunamis originate as a result of underwater earthquakes.
Tsunamis are primarily generated by earthquakes in subduction zones. In these zones one section of the Earth's crust, called a tectonic plate, moves over or under another. A giant rupture causes the seafloor to warp, displacing a vast amount of seawater. This raises the sea level and sets off the tsunami.
(By contrast, an earthquake along a strike-slip fault, where the tectonic plates grind against each other sideways, will not lift or drop the ocean floor.)
A 9.2 magnitude earthquake on the Aleutian Trench fault off Alaska in 1964 triggered a huge tsunami that killed more than 100 people, including 11 in Crescent City, California, where the tsunami crashed onto the shores hours after it originated.
Perhaps the biggest threat to the U.S. Pacific coast, however, is the Cascadia subduction zone, which extends from southern British Columbia to northern California.
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