PreliminaryAlaska Earthquake81y ago
M8.6 earthquake in The 1946 Unimak Island, Alaska Earthquake
Monday, April 1, 1946, 12:29:01 UTC · 53.492°N, 162.832°W
A magnitude 8.6 earthquake struck in The 1946 Unimak Island, Alaska Earthquake on Monday, April 1, 1946, 12:29:01 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
- 8.6
- Great · mw
- Depth
- 15 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
120 megatons of TNT
That is about 7,955 times the Hiroshima bomb. It released about 251,189 times the energy of a magnitude 5.0.
Tectonic setting
23 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 400 km
USGS lists 7 M2.5+ earthquakes within 400 km in the following 30 days; the largest was M6.6 on April 1, 1946. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 6.2184 km SE of Akutan, Alaska81y ago · 54 km SW of this epicenter
- 6.0155 km S of False Pass, Alaska81y ago · 42 km W of this epicenter
- 6.1136 km ESE of Akutan, Alaska81y ago · 76 km W of this epicenter
- 6.2172 km SSE of False Pass, Alaska81y ago · 17 km S of this epicenter
- 6.2136 km S of False Pass, Alaska81y ago · 64 km W of this epicenter
- 6.6146 km ESE of Akutan, Alaska81y ago · 63 km W of this epicenter
- 6.2136 km SE of Akutan, Alaska81y ago · 82 km W of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 38 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 · 254 km NE of this epicenter
- 7.0203 km SSE of Unalaska, AlaskaAugust 22, 1940 · 233 km SW of this epicenter
- 6.873 km SW of Sand Point, AlaskaJuly 2, 1922 · 182 km NE of this epicenter
- 6.768 km SSE of King Cove, AlaskaApril 29, 1937 · 133 km NE of this epicenter
- 6.6291 km S of Sand Point, AlaskaMay 13, 1910 · 222 km E of this epicenter
- 6.672 km SE of Sand Point, AlaskaOctober 16, 1932 · 264 km NE of this epicenter
- 6.559 km ESE of Akutan, AlaskaApril 2, 1922 · 147 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, which together caused about 168 recorded deaths. The most severe:
- 1946M8.6
Unimak Island
1 Apr 1946 · 0 km away · intensity VI
168 deaths$26 million damagetsunami
- 1788M8.0
Alaska Peninsula
6 Aug 1788 · 206 km away
tsunami
- 1820
East Aleutian Islands
1 Mar 1820 · 165 km away
tsunami
- 1868
Alaska Peninsula
15 May 1868 · 206 km away
tsunami
- 1878
East Aleutian Islands
29 Aug 1878 · 236 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.