The April 15, 1940 earthquake
M7.0near Attu Station, Alaska
A magnitude 7.0 earthquake 18.6 miles deep, 9.4 miles off Aleutians West Census Area. The 52nd 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
- 7.0
- moment magnitude (mw)
- Depth
- 18.6 mi
- 30.0 km below the surface
- Local time
- Monday, April 15, 1940
- 19:07 NST; 06:07 UTC on Apr 16, 1940
- In Alaska’s record
- 52nd
- strongest of 124,625 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event iscgem901282 (“80 km SSE 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 27 miles of the epicentre in the 30 days after.
1
Aftershocks in 30 days
6.4
Largest aftershock, May 11, 1940
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 · 9.4 mi
Earthquakes around the epicentre
258 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
- November 13, 1911M6.8
- February 22, 1935M6.8
- October 18, 1912M6.7
- July 22, 1923M6.5
- May 30, 1931M6.0
- December 17, 1929M5.7
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.