Reviewed by USGSAlaska Earthquake89y ago
M8.2 earthquake 1938 Semidi Islands, Alaska Earthquake
Thursday, November 10, 1938, 20:18:49 UTC · 55.178°N, 158.181°W
A magnitude 8.2 earthquake struck 1938 Semidi Islands, Alaska Earthquake on Thursday, November 10, 1938, 20:18:49 UTC, at a depth of 35.0 km (shallow). No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.
- Magnitude
- 8.2
- Great · mw
- Depth
- 35 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: 400 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
33 megatons of TNT
That is about 2,216 times the Hiroshima bomb. It released about 69,984 times the energy of a magnitude 5.0.
Tectonic setting
115 km
from the nearest mapped plate boundary, between the North American and Pacific 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 400 km
USGS lists 7 M2.5+ earthquakes within 400 km in the following 30 days; the largest was M6.9 on November 17, 1938. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 6.319 km SW of Old Harbor, Alaska89y ago · 357 km NE of this epicenter
- 6.9105 km ESE of Perryville, Alaska89y ago · 38 km NE of this epicenter
- 6.0168 km SE of Chignik, Alaska89y ago · 109 km E of this epicenter
- 5.963 km S of Sand Point, Alaska89y ago · 164 km W of this epicenter
- 6.1149 km S of Akhiok, Alaska89y ago · 255 km E of this epicenter
- 5.9124 km SSW of Akhiok, Alaska89y ago · 217 km NE of this epicenter
- 6.6104 km SSE of Perryville, Alaska89y ago · 34 km SW of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 28 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 110 km W of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 115 km NE of this epicenter
- 6.873 km SW of Sand Point, AlaskaJuly 2, 1922 · 198 km W of this epicenter
- 6.768 km SSE of King Cove, AlaskaApril 29, 1937 · 242 km W of this epicenter
- 6.6128 km SE of Chignik, AlaskaJuly 28, 1934 · 104 km NE of this epicenter
- 6.6291 km S of Sand Point, AlaskaMay 13, 1910 · 288 km S of this epicenter
- 6.672 km SE of Sand Point, AlaskaOctober 16, 1932 · 95 km W of this epicenter
- 6.5Bristol Bay, AlaskaAugust 22, 1907 · 268 km NW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 4 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1938M8.2
Alaska
10 Nov 1938 · 36 km away · intensity VI
tsunami
- 1788M8.0
Alaska Peninsula
6 Aug 1788 · 180 km away
tsunami
- 1868
Alaska Peninsula
15 May 1868 · 180 km away
tsunami
- 1880
Alaska Peninsula
29 Sep 1880 · 177 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.