The August 28, 1943 earthquake
M5.3near Big Bear Lake, CA
A magnitude 5.3 earthquake 3.7 miles deep, centred in San Bernardino County. The 294th strongest in California’s record since 1900, and the strongest within 50 miles since a magnitude 5.3 on May 17, 1940. 4 aftershocks of magnitude 2.5 or more followed within 30 days.
The earthquake
- Magnitude
- 5.3
- local magnitude (ml)
- Depth
- 3.7 mi
- 6.0 km below the surface
- Local time
- Saturday, August 28, 1943
- 20:45 PWT; 03:45 UTC on Aug 29, 1943
- In California’s record
- 294th
- strongest of 97,065 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event ci3366373 (“6km WNW of Big Bear Lake, CA”). 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.
4
Aftershocks in 30 days
4.0
Largest aftershock, Aug 29, 1943
2
On the first day
1
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
- San Bernardino CountyCA · inside
- Riverside CountyCA · 16.3 mi
- Los Angeles CountyCA · 38.8 mi
- Orange CountyCA · 48.0 mi
Cities, largest first
- RiversideCA · 33.3 mi
- San BernardinoCA · 20.6 mi
- FontanaCA · 30.3 mi
- Moreno ValleyCA · 27.4 mi
- OntarioCA · 39.8 mi
- Rancho CucamongaCA · 35.5 mi
- CoronaCA · 44.2 mi
- PomonaCA · 47.6 mi
- VictorvilleCA · 28.4 mi
- MenifeeCA · 41.8 mi
- MurrietaCA · 49.7 mi
- Jurupa ValleyCA · 34.0 mi
Earthquakes around the epicentre
3,255 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
- April 21, 1918M6.7
- July 22, 1923M6.2
- May 15, 1910M6.0
- May 17, 1940M5.3
- September 19, 1907M5.3
- January 15, 1930M5.2
- May 17, 1940M5.2
- September 26, 1929M5.1
- January 15, 1930M5.1
- April 10, 1910M5.0
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.