The 2011 Tōhoku earthquake occurred at the Japan Trench, where the Pacific Plate subducts beneath the plate carrying northeastern Japan. On March 11, 2011, this convergent plate boundary generated a magnitude 9.0–9.1 undersea megathrust earthquake off Honshu’s northeastern coast.
At a subduction zone, one tectonic plate is forced beneath another. Stress can build for centuries as the plates remain partly locked, then release suddenly when the seafloor slips. During the Tōhoku earthquake, a huge section of the plate boundary ruptured, lifting the ocean floor and displacing seawater. The resulting tsunami caused widespread destruction along Japan’s Pacific coast.
The rupture extended for roughly 500 kilometers and lasted about six minutes. The Japan Trench had long been recognized as a source of major earthquakes, but the event’s exceptional size surprised many scientists. It also prompted reassessment of historical evidence, including deposits linked to the ninth-century Sanriku earthquake. The Aleutian, Philippine and Mariana trenches are real subduction zones, but none hosted this particular earthquake.