An 8.9-magnitude earthquake struck off the coast of Japan today, triggering a massive tsunami that has killed hundreds and rolled all the way to the west coast of the United States. What happened in the earth’s crust? Why did this quake trigger such a major tsunami? Was this along a major fault line? Is there a connection to the recent earthquake in New Zealand? We ask Linda Lastowka, geophysicist at the U.S. Geological Survey’s National Earthquake Information Center.