The January 12, 1955 earthquake

M6.8near Nikolski, Alaska

A magnitude 6.8 earthquake 10.9 miles deep, 6.2 miles off Aleutians West Census Area. The 93rd strongest in Alaska’s record since 1900, and the strongest within 50 miles in the catalogue, which runs from 1900. 1 aftershock of magnitude 2.5 or more followed within 30 days.

The earthquake

Magnitude: 6.8; moment magnitude (mw)
Depth: 10.9 mi; 17.6 km below the surface
Local time: Wednesday, January 12, 1955; 16:03 AST; 02:03 UTC on Jan 13, 1955
Epicentre: 53.14°N, 167.70°W; 6.2 mi from Aleutians West Census Area
In Alaska’s record: 93rd; strongest of 124,625 since 1900
Within 50 miles: 1; county; more on this date

USGS ANSS Comprehensive Earthquake Catalog, event iscgem889117 (“81 km ENE of Nikolski, Alaska”). The USGS event page carries the ShakeMap, felt reports and the official summary.

Aftershocks

Earthquakes of magnitude 2.5 or more within 20 miles of the epicentre in the 30 days after.

Aftershocks in 30 days

6.5

Largest aftershock, Jan 13, 1955

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.
Before the modern seismic networks of the 1970s many small aftershocks went unrecorded, so early sequences read short.

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 · 6.2 mi

Earthquakes around the epicentre

1,627 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

January 11, 1907M6.3
January 12, 1952M6.3
September 4, 1942M6.2
January 20, 1952M6.2
July 24, 1938M6.1
April 3, 1935M6.0
September 1, 1942M6.0
August 14, 1931M6.0
August 14, 1931M5.8
September 10, 1939M5.6

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