On 11 March 2011, at 14:46 JST, a Mw 9.0–9.1 undersea megathrust earthquake occurred in the Pacific Ocean, 72 km (45 mi) east of the Oshika Peninsula of the Tōhoku region. It lasted approximately six minutes, causing a tsunami. It is sometimes known in Japan as the "Great East Japan Earthquake" , among other names. The disaster is often referred to by its numerical date, 3.11.

The Oshika Peninsula also pronounced "Ojika" is a peninsula which projects southeast into the Pacific Ocean from the coast of Miyagi Prefecture in northeast Honshu, the main island of Japan.