The April 26, 1981 earthquake
M5.8Westmorland, California
A magnitude 5.8 earthquake 11.7 miles deep, centred in Imperial County. The 131st strongest in California’s record since 1900, and the strongest within 50 miles since a magnitude 5.8 on October 15, 1979. 80 aftershocks of magnitude 2.5 or more followed within 30 days.
Watch the sequence unfoldMagnitude 5.8 · April 26, 1981
How the ground moved
Every recorded earthquake in the sequence, in order, from the foreshocks to a month after.
The earthquake
- Magnitude
- 5.8
- local magnitude (ml)
- Depth
- 11.7 mi
- 18.9 km below the surface
- Local time
- Sunday, April 26, 1981
- 05:09 PDT; 12:09 UTC
- In California’s record
- 131st
- strongest of 97,065 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event ci514869 (“The 1981 Westmorland, California Earthquake”). 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.
80
Aftershocks in 30 days
4.2
Largest aftershock, Apr 26, 1981
58
On the first day
31
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
- Imperial CountyCA · inside
- San Diego CountyCA · 26.5 mi
Earthquakes around the epicentre
2,796 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 18, 1940M6.9
- October 21, 1942M6.6
- April 8, 1968M6.6
- March 19, 1954M6.4
- October 15, 1979M6.4
- April 18, 1906M6.3
- March 25, 1937M6.0
- June 22, 1915M6.0
- January 1, 1927M6.0
- January 24, 1951M6.0
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.