Reviewed by USGSJapan59y ago
M5.5 earthquake 74 km S of Honchō, Japan
Friday, May 31, 1968, 19:51:58 UTC · 41.459°N, 142.834°E
A magnitude 5.5 earthquake struck 74 km S of Honchō, Japan on Friday, May 31, 1968, 19:51:58 UTC, at a depth of 22.7 km (shallow). It is the strongest earthquake within 300 km since an M5.6 on May 25, 1968.
- Magnitude
- 5.5
- Moderate · mw
- Depth
- 23 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 75 km aftershock search area
In context
How big was it, and why here?
Energy released
3 kilotons of TNT
That is about 1/5 of the Hiroshima bomb. It released about 7 times the energy of a magnitude 5.0.
Tectonic setting
151 km
from the nearest mapped plate boundary, between the Pacific and Okhotsk plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.
Depth: shallow
23 km
Shallow earthquakes (under 70 km) produce the strongest surface shaking for their size, so they are the ones most likely to cause damage near the epicenter.
Did You Feel It?
Where it was felt
No “Did You Feel It?” reports have been published for this event yet. If you felt it, you can add your report on the USGS website.
I felt it — report to USGS ↗USGS PAGER estimate
Who was exposed to shaking
USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No PAGER estimate is available for this event.
After the main event
Aftershocks within 75 km
USGS lists 3 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M6.3 on June 17, 1968. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 337 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.41933 Sanriku (Sanriku-oki) Earthquake, JapanMarch 2, 1933 · 291 km SE of this epicenter
- 8.21968 Tokachi-Oki EarthquakeMay 16, 1968 · 77 km SE of this epicenter
- 8.11952 Tokachi-Oki EarthquakeMarch 4, 1952 · 112 km NE of this epicenter
- 8.0113 km ENE of Miyako, JapanMarch 20, 1960 · 180 km S of this epicenter
- 7.978 km E of Hachinohe, JapanMarch 9, 1931 · 103 km S of this epicenter
- 7.970 km S of Honchō, JapanMay 16, 1968 · 5 km NE of this epicenter
- 7.7277 km SSE of Kushiro, JapanMay 3, 1919 · 251 km E of this epicenter
- 7.5Near the east coast of Honshu, JapanAugust 9, 1901 · 105 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 51 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 32,296 recorded deaths. The most severe:
- 1896M8.3
Sanriku
15 Jun 1896 · 239 km away
27,122 deathsExtreme damage ($25M+)tsunami
- 1933M8.4
Sanriku
2 Mar 1933 · 291 km away
3,022 deathsExtreme damage ($25M+)tsunami
- 1766M6.9
Hirosaki
8 Mar 1766 · 189 km away
1,700 deathsSevere damage ($5–24M)tsunami
- 1896
Senhoku, Ugo
31 Aug 1896 · 224 km away
206 deathsExtreme damage ($25M+)
- 1704
N Of Nosiro
27 May 1704 · 283 km away
58 deathsSevere damage ($5–24M)
- 1968M8.2
Off East Coast Of Honshu Island
16 May 1968 · 79 km away · intensity VI
52 deaths$131 million damagetsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.