September 2, 1923 Tsunami: Ryukyu Islands, Japan
A tsunami caused by a magnitude 7.7 earthquake began at Ryukyu Islands, Japan on September 2, 1923 at 02:46:40 UTC. The water rose as high as 0.3 meters. Its effects were recorded at 6 places in at least 2 countries.
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
- September 2, 1923, 02:46:40 UTC
- Source
- Ryukyu Islands, Japan
- Cause
- Earthquake
- Earthquake
- Magnitude 7.7, 20 km deep
- Maximum water height
- 0.3 m (1.0 ft)
- Runups recorded
- 6
- Tsunami intensity (Soloviev-Imamura)
- -1.5
- Tsunami magnitude (Iida)
- -1.7
- Waters
- Ocean
- How certain
- Definite tsunami
- Source location
- 34.900° N, 140.200° E
The toll
The record gives no deaths, injuries or damage for this tsunami.
What the record says
NCEI’s account, from the sources it cites.
September 2, 1923, 9:47 [local time], 35 N, 139.5 E, depth 20 km, magnitude 7.7. There was an earthquake with source at sea off the Boso Peninsula, which caused a weak tsunami. It was registered on the coast of Chiba Prefecture at Katsu'ura and off Cape Sunosaki, at Kamak'ura in Kanagawa Prefecture, and at Atami and Ito in Shizuoka Prefecture. The height of the wave was 0.3 m at Sunosaki Cape. The assumed travel time of the tsunami was 20 minutes to Mera and 40 minutes to Choshi. (reference #414)
September 2, 1923, 11:46 [Japanese local time], 34.9 N, 140.2 E, magnitude 7.3. (reference #150)
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 |
|---|---|---|---|---|---|---|---|
| Katsuura (Katsuurashi) | Japan | 30 | Eyewitness observation of water height | ||||
| Sunosaki | Japan | 41 | 0.3 | Eyewitness observation of water height | |||
| Kamakura | Japan | 75 | Eyewitness observation of water height | ||||
| Ito (Itoshi) | Japan | 101 | Eyewitness observation of water height | ||||
| Atami | Japan | 105 | Eyewitness observation of water height | ||||
| Tofino (Clayoquot),british Columbia, BC | Canada | 7,428 | 0.05 | Tide gauge (half the maximum wave height) | day 2, 15:47 |
More
Every tsunami in 1923The 1900sTsunamis of JapanThe earthquakeThis day in weather historyAlerts 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 1527.