What is the name of the tsunami that struck Japan in 869 AD?

The tsunami that struck Japan in 869 AD is known as the Jōgan tsunami. It followed the 869 Jōgan earthquake, which occurred near the Pacific coast of northeastern Honshu and flooded the Sendai Plain.

The event is described in the Nihon Sandai Jitsuroku, a Japanese imperial chronicle compiled in 901. The account records severe flooding and destruction around Tagajō, then an important administrative centre in Mutsu Province. Later geological studies found tsunami deposits extending at least four kilometres inland.

Jōgan was the Japanese era name in use at the time, lasting from 859 to 877, so the event is also called the 869 Jōgan earthquake or the Jōgan Sanriku earthquake. Researchers estimate that the earthquake may have been magnitude 8.6 or larger, possibly approaching magnitude 9.0. Its inundation pattern closely resembles that of the 2011 Tōhoku tsunami.