The February 6, 1964 earthquake
M6.9near Akhiok, Alaska
A magnitude 6.9 earthquake 16.0 miles deep, 6.0 miles off Kodiak Island Borough. The 72nd strongest in Alaska’s record since 1900, and the strongest within 50 miles since a magnitude 6.9 on February 13, 1951. 1 aftershock of magnitude 2.5 or more followed within 30 days.
The earthquake
- Magnitude
- 6.9
- moment magnitude (mw)
- Depth
- 16.0 mi
- 25.7 km below the surface
- Local time
- Thursday, February 6, 1964
- 03:07 AST; 13:07 UTC
- In Alaska’s record
- 72nd
- strongest of 124,625 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event iscgem870409 (“171 km SW of Akhiok, Alaska”). The USGS event page carries the ShakeMap, felt reports and the official summary.
Aftershocks
Earthquakes of magnitude 2.5 or more within 22 miles of the epicentre in the 30 days after.
1
Aftershocks in 30 days
5.9
Largest aftershock, Feb 6, 1964
1
On the first day
0
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
- Kodiak Island BoroughAK · 6.0 mi
Earthquakes around the epicentre
387 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
- July 28, 1934M6.6
- February 25, 1953M6.3
- May 8, 1939M6.2
- November 10, 1944M6.2
- March 16, 1940M6.1
- September 12, 1911M6.1
- November 15, 1955M6.1
- June 27, 1948M6.0
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.