869 Sanriku earthquake
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| Date | 9 July 869 |
|---|---|
| Magnitude | 8.4–9.0 Mw |
| Epicenter | 38°30′N 143°48′E / 38.5°N 143.8°ECoordinates: 38°30′N 143°48′E / 38.5°N 143.8°E |
| Areas affected |
Miyagi Prefecture Japan |
| Tsunami | Yes |
| Casualties | ≈1,000 |
The 869 Sanriku earthquake (貞観地震 Jōgan jishin?) and associated tsunami struck the area around Sendai in the northern part of Honshu on 9 July (26th day of 5th month, 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, with sand deposits being found up to 4 kilometres (2.5 mi) from the coast.
In Japan this earthquake is commonly called "Jogan Jishin(貞観地震)". 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.
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 reads as follows.
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