M8.4 earthquake 1933 Sanriku (Sanriku-oki) Earthquake, Japan

Thursday, March 2, 1933, 17:31:00 UTC · 39.209°N, 144.590°E

A magnitude 8.4 earthquake struck 1933 Sanriku (Sanriku-oki) Earthquake, Japan on Thursday, March 2, 1933, 17:31:00 UTC, at a depth of 15.0 km (shallow). No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.

Magnitude: 8.4; Great · mw
Depth: 15 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: V; Moderate (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 400 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

60 megatons of TNT

That is about 3,987 times the Hiroshima bomb. It released about 125,893 times the energy of a magnitude 5.0.

Tectonic setting

34 km

from the nearest mapped plate boundary, between the Pacific and Okhotsk plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.

Depth: shallow

15 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 400 km

USGS lists 15 M2.5+ earthquakes within 400 km in the following 30 days; the largest was M6.4 on March 3, 1933. 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 87 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 30 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 30,990 recorded deaths. The most severe:

1896M8.3
Sanriku
15 Jun 1896 · 60 km away
27,122 deathsExtreme damage ($25M+)tsunami
1933M8.4
Sanriku
2 Mar 1933 · 0 km away
3,022 deathsExtreme damage ($25M+)tsunami
1793M8.3
Sanriku,Rikuzen,Rikuchu
17 Feb 1793 · 94 km away
745 deathsSevere damage ($5–24M)tsunami
1905M7.0
Off Fukushima
6 Jul 1905 · 266 km away
57 deathstsunami
1856M8.0
Oshima
23 Aug 1856 · 171 km away · intensity V
26 deathsModerate damage ($1–5M)tsunami
1901M8.2
Off Northeast Coast Honshu
9 Aug 1901 · 249 km away
18 deathsModerate damage ($1–5M)tsunami

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

Nearby trackers