Reviewed by USGSAlaska87y ago
M7.0 earthquake 203 km SSE of Unalaska, Alaska
Thursday, August 22, 1940, 03:27:20 UTC · 52.158°N, 165.500°W
A magnitude 7.0 earthquake struck 203 km SSE of Unalaska, Alaska on Thursday, August 22, 1940, 03:27:20 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
- 7.0
- Strong · mw
- Depth
- 15 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 earthquake
In context
How big was it, and why here?
Energy released
415 kilotons of TNT
That is about 28 times the Hiroshima bomb. It released about 871 times the energy of a magnitude 5.0.
Tectonic setting
46 km
from the nearest mapped plate boundary, between the North American and Pacific 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 100 km
USGS has not published any M2.5+ earthquake within 100 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 27 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 6.977 km SSW of Nikolski, AlaskaJanuary 23, 1935 · 268 km W of this epicenter
- 6.846 km SSW of Nikolski, AlaskaJuly 22, 1933 · 258 km W of this epicenter
- 6.7103 km SE of Nikolski, AlaskaFebruary 20, 1916 · 147 km W of this epicenter
- 6.559 km ESE of Akutan, AlaskaApril 2, 1922 · 199 km N of this epicenter
- 6.596 km SSE of Nikolski, AlaskaSeptember 8, 1909 · 195 km W of this epicenter
- 6.569 km S of Nikolski, AlaskaAugust 12, 1932 · 218 km W of this epicenter
- 6.358 km SE of Nikolski, AlaskaJanuary 12, 1907 · 191 km W of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 5 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1902M7.8
Aleutian Islands: Fox Islands
1 Jan 1902 · 139 km away
- 1907M7.8
Aleutian Islands
2 Sep 1907 · 291 km away
- 1820
East Aleutian Islands
1 Mar 1820 · 269 km away
tsunami
- 1872
Aleutian Islands: Fox Islands
23 Aug 1872 · 205 km away
tsunami
- 1878
East Aleutian Islands
29 Aug 1878 · 171 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.