The June 28, 1991 earthquake
M5.8Sierra Madre, California
A magnitude 5.8 earthquake 5.0 miles deep, centred in Los Angeles County. The 108th strongest in California’s record since 1900, and the strongest within 50 miles since a magnitude 5.9 on October 1, 1987. 13 aftershocks of magnitude 2.5 or more followed within 30 days.
Watch the sequence unfoldMagnitude 5.8 · June 28, 1991
How the ground moved
Every recorded earthquake in the sequence, in order, through the month after.
The earthquake
- Magnitude
- 5.8
- moment magnitude (mw)
- Depth
- 5.0 mi
- 8.0 km below the surface
- Local time
- Friday, June 28, 1991
- 07:43 PDT; 14:43 UTC
- In California’s record
- 108th
- strongest of 97,065 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event ci2021449 (“The 1991 Sierra Madre, 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.
13
Aftershocks in 30 days
4.3
Largest aftershock, Jun 28, 1991
11
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.
Counties and cities within 50 miles
Distance from the epicentre to each county boundary (zero when inside) and to each city centre.
Counties
- Los Angeles CountyCA · inside
- San Bernardino CountyCA · 19.8 mi
- Orange CountyCA · 22.4 mi
- Riverside CountyCA · 29.7 mi
- Ventura CountyCA · 36.6 mi
- Kern CountyCA · 43.3 mi
Cities, largest first
- Los AngelesCA · 29.5 mi
- Long BeachCA · 35.3 mi
- AnaheimCA · 31.6 mi
- RiversideCA · 41.3 mi
- IrvineCA · 42.8 mi
- Santa AnaCA · 37.4 mi
- Santa ClaritaCA · 30.7 mi
- San BernardinoCA · 40.9 mi
- FontanaCA · 32.3 mi
- Huntington BeachCA · 39.5 mi
- GlendaleCA · 15.7 mi
- OntarioCA · 27.4 mi
Earthquakes around the epicentre
1,241 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
- February 9, 1971M6.6
- March 10, 1933M6.4
- July 22, 1923M6.2
- October 1, 1987M5.9
- February 9, 1971M5.8
- February 9, 1971M5.8
- February 28, 1990M5.5
- February 9, 1971M5.3
- August 4, 1927M5.3
- March 10, 1933M5.3
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.