Reviewed by USGSAlaska52y ago
M4.2 earthquake 203 km SE of Attu Station, Alaska
Friday, February 21, 1975, 01:26:41 UTC · 51.564°N, 175.299°E
A magnitude 4.2 earthquake struck 203 km SE of Attu Station, Alaska on Friday, February 21, 1975, 01:26:41 UTC, at a depth of 52.0 km (shallow).
- Magnitude
- 4.2
- Light · mb
- Depth
- 52 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
30 tons of TNT
That is about 1/500 of the Hiroshima bomb. A magnitude 5.0 releases about 16 times more energy.
Tectonic setting
41 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
52 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 50 km
USGS has not published any M2.5+ earthquake within 50 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 216 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.71965 Western Aleutian Islands (Hawadax/Rat Islands) EarthquakeFebruary 4, 1965 · 239 km E of this epicenter
- 8.31906 Western Aleutian Islands (Hawadax/Rat Islands) EarthquakeAugust 17, 1906 · 201 km E of this epicenter
- 7.993 km NW of Attu Station, AlaskaDecember 17, 1929 · 296 km NW of this epicenter
- 7.6Rat Islands, Aleutian Islands, AlaskaMarch 30, 1965 · 230 km SE of this epicenter
- 7.636 km NE of Attu Station, AlaskaFebruary 2, 1975 · 211 km NW of this epicenter
- 7.4265 km WSW of Adak, AlaskaFebruary 4, 1965 · 297 km E of this epicenter
- 7.4151 km S of Attu Station, AlaskaSeptember 2, 1907 · 172 km W of this epicenter
- 7.2238 km SSE of Attu Station, AlaskaSeptember 8, 1939 · 67 km S 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. The most severe:
- 1975M7.6
Aleutian Islands: Near Islands
2 Feb 1975 · 211 km away · intensity IX
Moderate damage ($1–5M)
- 1965M8.7
Aleutian Islands: Rat Islands
4 Feb 1965 · 239 km away · intensity VI
Under $1 million damagetsunami
- 1906M8.3
Aleutian Islands: Rat Islands
17 Aug 1906 · 201 km away
- 1909M7.8
Aleutian Islands
10 Apr 1909 · 53 km away
- 1929M7.8
Aleutian Islands: Near Islands
17 Dec 1929 · 280 km away
- 1898M7.6
Aleutian Islands: Near Islands
29 Jun 1898 · 232 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.