Reviewed by USGSAlaska70y ago
M6.8 earthquake 167 km W of Nikolski, Alaska
Thursday, February 21, 1957, 14:30:10 UTC · 52.925°N, 171.345°W
A magnitude 6.8 earthquake struck 167 km W of Nikolski, Alaska on Thursday, February 21, 1957, 14:30:10 UTC, at a depth of 104.1 km (intermediate). It is the strongest earthquake within 300 km since an M6.8 on November 1, 1946.
- Magnitude
- 6.8
- Strong · mw
- Depth
- 104 km
- Intermediate
- 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: 100 km aftershock search area
In context
How big was it, and why here?
Energy released
284 kilotons of TNT
That is about 19 times the Hiroshima bomb. It released about 596 times the energy of a magnitude 5.0.
Tectonic setting
180 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: intermediate
104 km
Intermediate-depth earthquakes usually break inside a plate that is sinking into the mantle. Shaking spreads over a wide area but is gentler at the epicenter than a shallow quake of the same size.
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 lists 1 M2.5+ earthquake within 100 km in the following 30 days; the largest was M6.0 on March 18, 1957. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 72 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.8234 km SSW of Nikolski, AlaskaMarch 7, 1929 · 249 km SE of this epicenter
- 7.4133 km WNW of Nikolski, AlaskaApril 18, 1916 · 73 km NE of this epicenter
- 6.9182 km SSE of Atka, AlaskaJanuary 27, 1906 · 255 km SW of this epicenter
- 6.977 km SSW of Nikolski, AlaskaJanuary 23, 1935 · 145 km SE of this epicenter
- 6.857 km SSW of Atka, AlaskaNovember 1, 1946 · 250 km SW of this epicenter
- 6.881 km ENE of Nikolski, AlaskaJanuary 13, 1955 · 245 km E of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 8 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1901M7.8
Aleutian Islands: Fox Islands
31 Dec 1901 · 166 km away
Limited damage (under $1M)tsunami
- 1917M7.9
Alaska Peninsula
31 May 1917 · 254 km away · intensity V
- 1902M7.8
Aleutian Islands: Fox Islands
1 Jan 1902 · 266 km away
- 1907M7.8
Aleutian Islands
2 Sep 1907 · 115 km away
- 1929M7.8
Aleutian Islands: Fox Islands
7 Mar 1929 · 233 km away · intensity V
tsunami
- 1916M7.5
Aleutian Islands: Fox Islands
18 Apr 1916 · 99 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.