August 818 Tsunami: Tokaido, Japan
A tsunami caused by a magnitude 7.9 earthquake and a landslide began at Tokaido, Japan in August 818. Its effects were recorded at 1 place.
Where the waves reached
The source (white) and every runup with a place, colored by the water height recorded there. A ring is a runup NCEI marks doubtful.
- Under 1 m
- 1 to 3 m
- 3 to 10 m
- 10 to 30 m
- 30 m and more
- Height not recorded
The tsunami
- Date
- August 818
- Source
- Tokaido, Japan
- Cause
- Earthquake and landslide
- Earthquake
- Magnitude 7.9
- Runups recorded
- 1
- Tsunami intensity (Soloviev-Imamura)
- 1
- Tsunami magnitude (Iida)
- 2
- Waters
- Ocean
- How certain
- Definite tsunami
- Source location
- 35.200° N, 139.300° E
The toll
- Deaths
- Many (about 101 to 1,000)
Where the literature gives no number, NCEI records a description on a scale of 1 to 4, printed here in its words. Damage is in millions of US dollars of the year of the event, not adjusted for inflation.
What the record says
NCEI’s account, from the sources it cites.
818, August. Kanto, Sagami Bay, 35.2 N, 139.3 E, magnitude 7.9. Boso Peninsula was struck by a moderate tsunami. South Kanto landslide. Many deaths. (reference #150)
August 818. There was strong earthquake in the prefectures of Tokyo, Saitama, Ibaraki, Gumma, and Tochigi; and there was a tsunami in Sagami Gulf. (reference #414)
818, August. Tokaido, Sagami bay, 35.2 N, 139.3 E, magnitude 7.9 MS. Imamura considers this a distant tsunami, Kawasumi considers it associated with a probable Sanriku quake. Considering the season it seems just as likely to have been a storm surge. (reference #79)
Every runup
Nearest the source first. Heights are above sea level at the time; a tide gauge reads half the wave’s full height.
| Where | Country | Km from source | Water height, m | Inland, m | Measured by | First wave, UTC | Deaths |
|---|---|---|---|---|---|---|---|
| Boso Peninsula | Japan | 60 | Eyewitness observation of water height |
More
Every tsunami in 818The 800sTsunamis of JapanThe earthquakeAlerts in force
Sources
Tsunami events and runups from NOAA’s National Centers for Environmental Information, Global Historical Hazard Database, cited as NCEI/WDS, doi:10.7289/V5PN93H7. Public domain. Read 2026-09-24. NCEI tsunami event 66.