QuakeScout
Magnitude5.5

Reviewed by USGSAlaska62y ago

M5.5 earthquake 237 km ESE of Attu Station, Alaska

Thursday, April 22, 1965, 18:36:01 UTC · 51.719°N, 176.150°E

A magnitude 5.5 earthquake struck 237 km ESE of Attu Station, Alaska on Thursday, April 22, 1965, 18:36:01 UTC, at a depth of 27.6 km (shallow). It is the strongest earthquake within 300 km since an M5.8 on April 20, 1965.

Magnitude
5.5
Moderate · mw
Depth
28 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

3 kilotons of TNT

That is about 1/5 of the Hiroshima bomb. It released about 6 times the energy of a magnitude 5.0.

Tectonic setting

76 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

28 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 75 km

USGS has not published any M2.5+ earthquake within 75 km in the 30 days after this event.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 149 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

  1. 8.71965 Western Aleutian Islands (Hawadax/Rat Islands) EarthquakeFebruary 4, 1965 · 185 km E of this epicenter
  2. 8.31906 Western Aleutian Islands (Hawadax/Rat Islands) EarthquakeAugust 17, 1906 · 140 km E of this epicenter
  3. 7.6Rat Islands, Aleutian Islands, AlaskaMarch 30, 1965 · 200 km SE of this epicenter
  4. 7.4265 km WSW of Adak, AlaskaFebruary 4, 1965 · 240 km E of this epicenter
  5. 7.4151 km S of Attu Station, AlaskaSeptember 2, 1907 · 232 km W of this epicenter
  6. 7.2238 km SSE of Attu Station, AlaskaSeptember 8, 1939 · 115 km SW of this epicenter
  7. 7.2238 km WSW of Adak, AlaskaMarch 22, 1905 · 284 km E of this epicenter
  8. 7.0Rat Islands, Aleutian Islands, AlaskaFebruary 6, 1916 · 226 km SE of this epicenter

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 6 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

  1. 1965M8.7

    Aleutian Islands: Rat Islands

    4 Feb 1965 · 185 km away · intensity VI

    Under $1 million damagetsunami

  2. 1906M8.3

    Aleutian Islands: Rat Islands

    17 Aug 1906 · 140 km away

  3. 1909M7.8

    Aleutian Islands

    10 Apr 1909 · 85 km away

  4. 1898M7.6

    Aleutian Islands: Near Islands

    29 Jun 1898 · 287 km away

  5. 1965M7.6

    Aleutian Islands: Rat Islands

    30 Mar 1965 · 199 km away

    tsunami

  6. 1940M7.4

    Aleutian Islands: Rat Islands

    14 Jul 1940 · 144 km away

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

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