Japan earthquakes and the Ring of Fire

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Japan earthquakes and the Ring of Fire : The 6.9-magnitude earthquake last week off the coast of Fukushima, Japan, probably happened along the same fault that ruptured in 2011, unleashing a massive 9.0-magnitude temblor and resulting tsunami that caused widespread destruction. What makes this part of the world so susceptible to big earthquakes?

Japan lies along what is called the Pacific Ring of Fire, an imaginary horseshoe-shaped zone that follows the rim of the Pacific Ocean, where many of the world’s earthquakes and volcanic eruptions occur. According to the U.S. Geological Survey, 81 percent of the world’s largest earthquakes happen in this belt.

Within the Pacific Ring of Fire, several tectonic plates mash and collide. In what are known as subduction zones, one plate bends and slides underneath the other, causing the oceanic crust to sink into the Earth’s mantle.

“From Alaska down to Japan and the Philippines, all the way down around the western Pacific — and then the boundary of the west coast of South America and central America — are all big subduction zones,” said Robert Smith, an emeritus professor of geophysics at the University of Utah.

Japan itself sits atop a complex mosaic of tectonic plates that grind together and trigger earthquakes and volcanic eruptions, Smith said.