The quake was caused when one giant tectonic plate was shoved under another, the type of movement that produces the biggest earthquakes. It's the same kind of quake that caused the devastating 2004 Indonesian tsunami.
"You're looking at something that's rupturing a very significant patch of the Earth's crust," said David Applegate, senior science adviser at the U.S. Geological Survey. "If anyone is in the position to ride this out, it is the Japanese."
Image: People is dwarfed by a freighter sits on a breakwater in Kamaishi in Iwate Prefecture (state) in Japan on March 13, 2011, two days after the area was hit by Friday's catastrophic earthquake-triggered tsunami.