The and its associated tsunami struck the area around Sendai in the northern part of Honshu on 9 July 869 (the 26th day of the 5th month in the 11th year of Jōgan). The earthquake had an estimated magnitude of at least 8.4 on the moment magnitude scale, but may have been as high as 9.0, similar to the 2011 Tōhoku earthquake and tsunami. The tsunami caused widespread flooding of the Sendai plain. In 2001, researchers identified sand deposits in a trench more than from the coast as coming from this tsunami. Name In Japan this earthquake is commonly called . Jōgan is the Japanese era name for the period from 859 to 877 AD. But during the era other large earthquakes also occurred in Japan, so the name of the geographic epicenter and the anno domini year number when the quake occurred are sometimes added. Sanriku in this context is a name roughly corresponding to the Pacific front northeastern coastal area of Honshu island. The Japanese history text, Nihon Sandai Jitsuroku which was compiled in 901, recorded the 869 earthquake and tsunami of Mutsu Province. Description in public archives Although this earthquake occurred in the frontier region of the ancient Japanese Empire based at Kyoto, a short and precise official record of this catastrophe was left. The description in Nihon Sandai Jitsuroku [True History of Three Reigns of Japan] (901) reads as follows: Tectonic setting The northern part of Honshu lies above the convergent boundary between the over-riding Okhotsk Plate (a proposed microplate within the North American Plate) and the subducting Pacific Plate. This boundary has been associated with a series of large historical earthquakes, originating either from rupture along the plate interface or from deformation within either the over-riding or subducting plates, many of them triggering a destructive tsunami, such as the 1896 Sanriku earthquake. Damage In the area which the earthquake struck, the Imperial Court of Japan battled with an indigenous people of the Tōhoku region, Emishi, at that time. According to Nihon Sandai Jitsuroku, around 1,000 people were killed by the tsunami. There are legends about the earthquake from Tōhoku region to Bōsō Peninsula. The tsunami caused extensive flooding of the Sendai plain, determined to have reached at least inland, destroying the town of Tagajō and its castle. Archaeological investigations have identified the remains of 8th and 9th century buildings beneath the town, covered by sediments