April 1, 1968 Tsunami: Seikaido, Japan

Name: April 1, 1968 Tsunami: Seikaido, Japan
Start: 1968-04-01
Location: Seikaido, Japan

April 1, 1968 · 3.07 m · 1 death · Definite tsunami

A tsunami caused by a magnitude 7.5 earthquake began at Seikaido, Japan on April 1, 1968 at 00:42:04 UTC. The water rose as high as 3.07 meters. Its effects were recorded at 62 places in at least 3 countries. It killed 1 person, counting the earthquake or eruption that caused it.

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

Tsunami warnings in force

The tsunami

Date: April 1, 1968, 00:42:04 UTC
Source: Seikaido, Japan
Cause: Earthquake
Earthquake: Magnitude 7.5, 30 km deep
Maximum water height: 3.07 m (10.1 ft)
Runups recorded: 62
Tsunami intensity (Soloviev-Imamura): 1
Tsunami magnitude (Iida): 1.3
Waters: Ocean
How certain: Definite tsunami
Source location: 32.300° N, 132.500° E

The toll

Deaths: 1 with the earthquake or eruption that caused it
Injuries: 22 with the earthquake or eruption that caused it
Damage: Limited (under about $1 million); Moderate (about $1 to $5 million) with the earthquake or eruption that caused it
Houses destroyed: 4; Some (about 51 to 100) with the earthquake or eruption that caused it

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.

Reference #414:

On April 1, 1968 at 9:42 [local time] there was a strong magnitude 7.7 earthquake with a sub-latitudinal source 60 km long between Kyushu and and Shikoku Islands (32.6 N, 132.2 E, depth 40 km).

A tsunami of moderate intensity occurred. It reached the nearest coasts of the islands of Shikoku and Kyusllu approximately 20 minutes after the earthquake. On the average, the range of the oscillations in sea level on these coasts was 2-2.5 m. The greatest rise of water, 3 m

or somewhat more, was resgistered on Shikoku Island at

Urashiri and Komame; here the water flooded across the protective dikes and caused destruction. At most points, however, the oscillations in level did not exceed the regular flood and ebb oscillations. The tsunami, on the basis of visual observations, began with a flood tide almost everywhere. The first or the second wave was the highest. As a rule, the water level rose quietly, and strong currents arose only in narrow straits. The mean period of oscillations was close to 20 minutes.

The tsunami was registered clearly by the tide gauges on the southern coast of Japan. The tsunami begins with a flood tide on all the tide gauge records. However, on the records of the instruments set up on Shikoku Island, the height of the first trough is approximately twice as great as the height of the first crest. For this reason, it has been surmised that there were subsidences of the floor in the southern part of the source of the tsunami, while elevations of the floor predominated on the whole at the source. According to Hatori, the vertical displacements of the sea bottom at the source of the tsunami were about 20 cm, and the energy of the tsunami was 1.3 X 1020 ergs. According to Aida, a comparatively uniform elevation of the bottom by 30-35 cm took place at the source, and the energy of the tsunami was (1.4-2.2) X 1019 ergs. It is conjectured that the earthquake was a consequence of gently sloping overthrust in a west to east direction.

Reference #45:

A 2.3 meter tsunami was generated on the east of Kyushu. It destroyed four homes and capsized several fishing boats.

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	Measured by	First wave, UTC
Kashiwajima	Japan	53	0.66	Tide gauge (half the maximum wave height)
Urajiri	Japan	56	3.07	Eyewitness observation of water height
Komame	Japan	57	3.06	Eyewitness observation of water height
Ohama	Japan	66	0.66	Eyewitness observation of water height
Tosa-Shimizu	Japan	68	1.16	Tide gauge (half the maximum wave height)	day 1, 01:03
Fukaura	Japan	73	1.72	Eyewitness observation of water height
Iwamizu	Japan	73	1.66	Eyewitness observation of water height
Sukumo	Japan	74	1.12	Tide gauge (half the maximum wave height)
Miyanoura	Japan	76	0.75	Tide gauge (half the maximum wave height)
Kamae	Japan	77	0.96	Eyewitness observation of water height
Hososhima (Ken)	Japan	79	0.99	Eyewitness observation of water height
Hososhima	Japan	80	0.7	Eyewitness observation of water height	day 1, 00:59
Hososhima	Japan	80	0.66	Tide gauge (half the maximum wave height)
Totoroko	Japan	80	1.01	Eyewitness observation of water height
Tomi	Japan	81	0.15
Hososhima (Hyuga City)	Japan	81	1.2	Eyewitness observation of water height
Toumi	Japan	81	0.14	Tide gauge (half the maximum wave height)
Urashiri, Shikoku Island	Japan	84	3	Eyewitness observation of water height
Shimoda	Japan	84	0.15	Tide gauge (half the maximum wave height)
Shimoda	Japan	84	0.15	Tide gauge (half the maximum wave height)
Takenoura	Japan	84	1.26	Eyewitness observation of water height
Nobeoka	Japan	85	0.14	Tide gauge (half the maximum wave height)	day 1, 01:00
Saiki	Japan	91	0.3	Tide gauge (half the maximum wave height)	day 1, 01:16
Saikiko	Japan	93	0.33	Tide gauge (half the maximum wave height)
Kamikawaguchiko	Japan	95	0.7	Tide gauge (half the maximum wave height)	day 1, 01:12
Uwajima	Japan	104	0.24	Tide gauge (half the maximum wave height)
Tsukumi	Japan	105	0.31	Tide gauge (half the maximum wave height)	day 1, 01:22
Usuki	Japan	111	0.68	Tide gauge (half the maximum wave height)
Saganoseki	Japan	120	0.06	Tide gauge (half the maximum wave height)
Yawatahama	Japan	128	0.4	Tide gauge (half the maximum wave height)	day 1, 01:34
Aburatsu	Japan	130	0.33	Tide gauge (half the maximum wave height)	day 1, 01:09
Oita	Japan	132	0.11	Tide gauge (half the maximum wave height)	day 1, 01:47
Tosa-Shimoda	Japan	160	0.1	Tide gauge (half the maximum wave height)	day 1, 01:10
Urado	Japan	165	0.21	Tide gauge (half the maximum wave height)	day 1, 01:29
Kochi	Japan	170	0.23	Tide gauge (half the maximum wave height)
Murotomisaki	Japan	189	0.43	Tide gauge (half the maximum wave height)	day 1, 01:15
Murotsu	Japan	189	0.6	Tide gauge (half the maximum wave height)
Tokuyama	Japan	203	0.04	Tide gauge (half the maximum wave height)
Odomari	Japan	223	0.4	Tide gauge (half the maximum wave height)	day 1, 01:38
Nishinoomote	Japan	225	0.16	Tide gauge (half the maximum wave height)
Makurazaki	Japan	238	0.11	Tide gauge (half the maximum wave height)
Komatsushima	Japan	272	0.11	Tide gauge (half the maximum wave height)
Fukura	Japan	299	0.12	Eyewitness observation of water height
Shirahama	Japan	310	0.08	Tide gauge (half the maximum wave height)
Sumoto	Japan	317	0.05	Tide gauge (half the maximum wave height)
Wakayama	Japan	326	0.11	Tide gauge (half the maximum wave height)	day 1, 01:50
Wakayama (Kitako)	Japan	326	0.16	Tide gauge (half the maximum wave height)
Kushimoto	Japan	333	0.43	Tide gauge (half the maximum wave height)	day 1, 01:24
Uragami	Japan	347	0.22	Tide gauge (half the maximum wave height)
Owase	Japan	398	0.2	Tide gauge (half the maximum wave height)	day 1, 01:32
Owase	Japan	398	0.23	Tide gauge (half the maximum wave height)
Nagashimako	Japan	414	0.12	Tide gauge (half the maximum wave height)
Nagoya Bay	Japan	511		Eyewitness observation of water height
Naze	Japan	521	0.1	Tide gauge (half the maximum wave height)
Minami-Izu	Japan	646	0.1	Tide gauge (half the maximum wave height)
Kozushima	Japan	653	0.1	Tide gauge (half the maximum wave height)	day 1, 01:59
Kozushima	Japan	653	0.1	Tide gauge (half the maximum wave height)
Kitaurako	Japan	1,073	0.75	Tide gauge (half the maximum wave height)
Urakami	Japan	1,423	0.2	Tide gauge (half the maximum wave height)	day 1, 01:23
Attu, Massacre Bay, AK, AK	United States	3,966	0.1	Tide gauge (half the maximum wave height)
Pago Pago, American Samoa, AS	US Territories	7,945		Tide gauge (half the maximum wave height)
Kitano'Ura	Japan		0.8	Tide gauge (half the maximum wave height)

Every tsunami in 1968 The 1900s Tsunamis of Japan The earthquake This day in weather history Alerts 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 1998.