The September 4, 1989 earthquake

M7.0near Chignik, Alaska

A magnitude 7.0 earthquake 6.8 miles deep, 41.7 miles off Kodiak Island Borough. The 55th strongest in Alaska’s record since 1900, and the strongest within 50 miles since a magnitude 7.0 on May 4, 1923. 1 aftershock of magnitude 2.5 or more followed within 30 days.

The earthquake

Magnitude: 7.0; moment magnitude (mw)
Depth: 6.8 mi; 11.0 km below the surface
Local time: Monday, September 4, 1989; 05:14 AKDT; 13:14 UTC
Epicentre: 55.32°N, 156.43°W; 41.7 mi from Kodiak Island Borough
In Alaska’s record: 55th; strongest of 124,625 since 1900
Within 50 miles: 1; county; more on this date

USGS ANSS Comprehensive Earthquake Catalog, event ak989bcpkhdo (“164 km SE of Chignik, Alaska”). The USGS event page carries the ShakeMap, felt reports and the official summary.

Aftershocks

Earthquakes of magnitude 2.5 or more within 25 miles of the epicentre in the 30 days after.

Aftershocks in 30 days

4.0

Largest aftershock, Sep 6, 1989

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

Kodiak Island BoroughAK · 41.7 mi

Earthquakes around the epicentre

255 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

May 4, 1923M7.0
February 13, 1951M6.9
February 6, 1964M6.9
February 12, 1979M6.7
July 28, 1934M6.6
March 16, 1940M6.1
November 15, 1955M6.1
November 15, 1938M6.0
November 7, 1928M6.0
February 6, 1964M5.9

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