The October 31, 1969 earthquake
M6.5near Adak, Alaska
A magnitude 6.5 earthquake 23.4 miles deep, 0.4 miles off Aleutians West Census Area. The 187th strongest in Alaska’s record since 1900, and the strongest within 50 miles since a magnitude 6.7 on September 11, 1969. 1 aftershock of magnitude 2.5 or more followed within 30 days.
The earthquake
- Magnitude
- 6.5
- moment magnitude (mw)
- Depth
- 23.4 mi
- 37.6 km below the surface
- Local time
- Friday, October 31, 1969
- 00:33 BST; 11:33 UTC
- In Alaska’s record
- 187th
- strongest of 124,625 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event iscgem803964 (“175 km WSW of Adak, 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.
1
Aftershocks in 30 days
6.0
Largest aftershock, Nov 6, 1969
0
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
- Aleutians West Census AreaAK · 0.4 mi
Earthquakes around the epicentre
3,932 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
- March 21, 1905M7.2
- March 15, 1957M7.2
- July 5, 1929M7.0
- March 11, 1957M7.0
- May 14, 1969M6.9
- March 30, 1913M6.9
- January 4, 1912M6.8
- October 12, 1926M6.7
- June 1, 1955M6.7
- June 20, 1955M6.7
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.