The February 1, 1975 earthquake

M7.6near Attu Station, Alaska

A magnitude 7.6 earthquake 6.2 miles deep, 15.3 miles off Aleutians West Census Area. The 17th strongest in Alaska’s record since 1900, and the strongest within 50 miles in the catalogue, which runs from 1900. 4 aftershocks of magnitude 2.5 or more followed within 30 days.

The earthquake

Magnitude: 7.6; surface-wave magnitude (ms)
Depth: 6.2 mi; 10.0 km below the surface
Local time: Saturday, February 1, 1975; 21:43 BST; 08:43 UTC on Feb 2, 1975
Epicentre: 53.11°N, 173.50°E; 15.3 mi from Aleutians West Census Area
In Alaska’s record: 17th; strongest of 124,625 since 1900
Within 50 miles: 1; county; more on this date

USGS ANSS Comprehensive Earthquake Catalog, event usp00009ry (“36 km NE of Attu Station, Alaska”). The USGS event page carries the ShakeMap, felt reports and the official summary.

Aftershocks

Earthquakes of magnitude 2.5 or more within 66 miles of the epicentre in the 30 days after.

Aftershocks in 30 days

5.4

Largest aftershock, Feb 9, 1975

On the first day

In the 7 days before

The search radius is the surface rupture length expected for an earthquake of this magnitude (Wells and Coppersmith, 1994), at least 20 and at most 600 miles, so a great earthquake's sequence is counted along its whole fault.

Counties and cities within 50 miles

Distance from the epicentre to each county boundary (zero when inside) and to each city centre.

Counties

Aleutians West Census AreaAK · 15.3 mi

Earthquakes around the epicentre

133 earthquakes of magnitude 3 or more within 50 miles of this epicentre since 1973.

Earlier earthquakes of magnitude 5 or more within 50 miles, strongest first

April 15, 1940M7.0
October 18, 1912M6.7
February 1, 1975M5.9
March 19, 1973M5.8
May 30, 1931M5.8
February 5, 1965M5.7
December 17, 1929M5.7
February 3, 1965M5.7
November 21, 1972M5.6
March 27, 1973M5.6

USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.