M7.9 earthquake 70 km S of Honchō, Japan

Thursday, May 16, 1968, 10:39:03 UTC · 41.498°N, 142.858°E

A magnitude 7.9 earthquake struck 70 km S of Honchō, Japan on Thursday, May 16, 1968, 10:39:03 UTC, at a depth of 31.1 km (shallow). It is the strongest earthquake within 300 km since an M8.2 on May 16, 1968.

Magnitude: 7.9; Major · mw
Depth: 31 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: VII; Very strong (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

11 megatons of TNT

That is about 709 times the Hiroshima bomb. It released about 22,387 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

31 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 200 km

USGS lists 26 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.7 on May 16, 1968. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 312 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

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 · 242 km away
27,122 deathsExtreme damage ($25M+)tsunami
1933M8.4
Sanriku
2 Mar 1933 · 294 km away
3,022 deathsExtreme damage ($25M+)tsunami
1766M6.9
Hirosaki
8 Mar 1766 · 192 km away
1,700 deathsSevere damage ($5–24M)tsunami
1896
Senhoku, Ugo
31 Aug 1896 · 229 km away
206 deathsExtreme damage ($25M+)
1704
N Of Nosiro
27 May 1704 · 286 km away
58 deathsSevere damage ($5–24M)
1968M8.2
Off East Coast Of Honshu Island
16 May 1968 · 83 km away · intensity VI
52 deaths$131 million damagetsunami

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

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