M7.4 earthquake 265 km WSW of Adak, Alaska

Thursday, February 4, 1965, 08:40:39 UTC · 51.436°N, 179.592°E

A magnitude 7.4 earthquake struck 265 km WSW of Adak, Alaska on Thursday, February 4, 1965, 08:40:39 UTC, at a depth of 9.0 km (shallow). It is the strongest earthquake within 300 km since an M8.7 on February 4, 1965.

Magnitude: 7.4; Major · mw
Depth: 9 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 earthquakeDashed circle: 200 km aftershock search area

In context

How big was it, and why here?

Energy released

1.8 megatons of TNT

That is about 122 times the Hiroshima bomb. It released about 3,846 times the energy of a magnitude 5.0.

Tectonic setting

100 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

9 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 200 km

USGS lists 7 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M5.8 on February 18, 1965. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 183 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

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. The most severe:

1965M8.7
Aleutian Islands: Rat Islands
4 Feb 1965 · 64 km away · intensity VI
Under $1 million damagetsunami
1906M8.3
Aleutian Islands: Rat Islands
17 Aug 1906 · 108 km away
1905M7.9
Andreanof Islands
14 Feb 1905 · 152 km away
1965M7.6
Aleutian Islands: Rat Islands
30 Mar 1965 · 170 km away
tsunami
1940M7.4
Aleutian Islands: Rat Islands
14 Jul 1940 · 115 km away

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

Nearby trackers