Reviewed by USGSJapan54y ago
M3.9 earthquake 197 km SSE of Katsuura, Japan
Wednesday, March 21, 1973, 05:23:34 UTC · 33.441°N, 140.946°E
A magnitude 3.9 earthquake struck 197 km SSE of Katsuura, Japan on Wednesday, March 21, 1973, 05:23:34 UTC, at a depth of 48.0 km (shallow).
- Magnitude
- 3.9
- Minor · mb
- Depth
- 48 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: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
11 tons of TNT
That is about 1/1,410 of the Hiroshima bomb. A magnitude 5.0 releases about 45 times more energy.
Tectonic setting
29 km
from the nearest mapped plate boundary, between the North American and African plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
48 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 50 km
USGS lists 6 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.4 on April 11, 1973. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 4.1227 km SSE of Tateyama, Japan54y ago · 42 km S of this epicenter
- 4.2190 km SSE of Katsuura, Japan54y ago · 7 km N of this epicenter
- 4.4190 km SSE of Tateyama, Japan54y ago · 8 km NW of this epicenter
- 3.9212 km SSE of Tateyama, Japan54y ago · 17 km S of this epicenter
- 4.2214 km SSE of Katsuura, Japan54y ago · 17 km SE of this epicenter
- 3.7169 km SSE of Tateyama, Japan54y ago · 30 km NW of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 245 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.05 km SSE of Ōiso, JapanSeptember 1, 1923 · 251 km NW of this epicenter
- 7.9174 km SE of Katsuura, JapanNovember 25, 1953 · 89 km NE of this epicenter
- 7.85 km E of Tateyama, JapanSeptember 2, 1923 · 196 km NW of this epicenter
- 7.450 km SSW of Ōyama, JapanJanuary 21, 1906 · 282 km W of this epicenter
- 7.3206 km SSE of Wada, JapanDecember 4, 1972 · 17 km SW of this epicenter
- 7.3190 km SE of Hasaki, JapanSeptember 7, 1906 · 206 km NE of this epicenter
- 7.264 km ENE of Hasaki, JapanJune 1, 1923 · 282 km N of this epicenter
- 7.238 km SSW of Shimoda, JapanOctober 24, 1905 · 218 km NW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 27 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 120,755 recorded deaths. The most severe:
- 1923M7.9
Tokyo, Yokohama
1 Sep 1923 · 227 km away
105,385 deaths$600 million damagetsunami
- 1855M7.0
Tokyo
11 Nov 1855 · 267 km away
6,757 deathsExtreme damage ($25M+)tsunami
- 1703M8.2
Off Sw Boso Peninsula
30 Dec 1703 · 194 km away
5,233 deathsExtreme damage ($25M+)tsunami
- 1707M8.4
Enshunada
28 Oct 1707 · 300 km away
2,000 deathsSevere damage ($5–24M)tsunami
- 1854M8.3
Enshunada Sea
23 Dec 1854 · 288 km away
1,000 deathsExtreme damage ($25M+)tsunami
- 1930M7.1
Honshu: Idu
25 Nov 1930 · 249 km away
259 deathsExtreme damage ($25M+)
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.