M7.8 earthquake 105 km E of Iwaki, Japan

Saturday, November 5, 1938, 08:43:24 UTC · 36.971°N, 142.065°E

A magnitude 7.8 earthquake struck 105 km E of Iwaki, Japan on Saturday, November 5, 1938, 08:43:24 UTC, at a depth of 35.0 km (shallow). It is the strongest earthquake within 300 km since an M7.8 on September 2, 1923.

Magnitude: 7.8; Major · mw
Depth: 35 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: VI; 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

7.6 megatons of TNT

That is about 502 times the Hiroshima bomb. It released about 15,849 times the energy of a magnitude 5.0.

Tectonic setting

106 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

35 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 33 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M7.7 on November 6, 1938. 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 156 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 46 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 15,545 recorded deaths. The most severe:

1855M7.0
Tokyo
11 Nov 1855 · 251 km away
6,757 deathsExtreme damage ($25M+)tsunami
1703M8.2
Off Sw Boso Peninsula
30 Dec 1703 · 287 km away
5,233 deathsExtreme damage ($25M+)tsunami
1828
Sandyo In Etigo
18 Dec 1828 · 235 km away
1,443 deathsExtreme damage ($25M+)tsunami
1793M8.3
Sanriku,Rikuzen,Rikuchu
17 Feb 1793 · 241 km away
745 deathsSevere damage ($5–24M)tsunami
1894M7.0
Syonai
22 Oct 1894 · 292 km away
726 deathsSevere damage ($5–24M)tsunami
1804M7.3
Kisakata
10 Jul 1804 · 296 km away
450 deathsExtreme damage ($25M+)tsunami

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

Nearby trackers