The largest earthquake in Japan's history started at 2:46 on a Friday afternoon, March 11, 2011, and finally stopped shaking several minutes later. Japan's early warning system did its job and so did the nation's well-constructed buildings, which limited the death toll to less than a thousand people. We will never know the exact number, though, because soon afterward gigantic tsunamis erased whole cities up and down the coast of the Tohoku district, the traditional region at the north end of Japan's main island Honshu. All told, some 20,000 people died in Japan that day.
Japanese scientists call this quake the Tohoku-Chiho Taiheiyo-Oki event, commonly translated as "off the Pacific coast of Tohoku." The rupture extended northward beyond Tohoku into Hokkaido, and great damage also occurred to the south in the Kanto region. The U.S. Geological Survey gave the earthquake the shorter name Tohoku for use in the scientific literature, although it's also called the Tohoku-oki ("Tohoku offshore") event. The Japanese government also calls it the Great East Japan Earthquake.
There's a wealth of scientific material online; here are some of my favorites: The US Geological Survey's poster about the event UNAVCO's index page listing dozens of worthy sites IRIS's "Teachable Moments" page on the quake Sound files that speed up the quake's seismographic record
