Reviewed by USGSAlaska70y ago
M6.8 earthquake 68 km SSW of Unalaska, Alaska
Friday, March 29, 1957, 05:10:33 UTC · 53.312°N, 166.949°W
A magnitude 6.8 earthquake struck 68 km SSW of Unalaska, Alaska on Friday, March 29, 1957, 05:10:33 UTC, at a depth of 25.0 km (shallow). It is the strongest earthquake within 300 km since an M7.1 on March 22, 1957.
- Magnitude
- 6.8
- Strong · mw
- Depth
- 25 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- VI
- Strong (ShakeMap)
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
274 kilotons of TNT
That is about 18 times the Hiroshima bomb. It released about 575 times the energy of a magnitude 5.0.
Tectonic setting
110 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
25 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 85 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.6The 1946 Unimak Island, Alaska EarthquakeApril 1, 1946 · 274 km E of this epicenter
- 7.4133 km WNW of Nikolski, AlaskaApril 18, 1916 · 247 km W of this epicenter
- 7.139 km S of Akutan, AlaskaMarch 22, 1957 · 94 km NE of this epicenter
- 7.135 km SW of Nikolski, AlaskaMarch 11, 1957 · 165 km SW of this epicenter
- 7.0203 km SSE of Unalaska, AlaskaAugust 22, 1940 · 161 km SE of this epicenter
- 6.980 km SW of Nikolski, AlaskaMarch 9, 1957 · 205 km SW of this epicenter
- 6.977 km SSW of Nikolski, AlaskaJanuary 23, 1935 · 199 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 9 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 · 274 km away · intensity VI
168 deaths$26 million damagetsunami
- 1917M7.9
Alaska Peninsula
31 May 1917 · 217 km away · intensity V
- 1902M7.8
Aleutian Islands: Fox Islands
1 Jan 1902 · 108 km away
- 1907M7.8
Aleutian Islands
2 Sep 1907 · 203 km away
- 1916M7.5
Aleutian Islands: Fox Islands
18 Apr 1916 · 203 km away
- 1957M7.5
Aleutian Islands: Fox Islands
22 Mar 1957 · 220 km away · intensity V
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.