The February 28, 1990 earthquake
M5.5Upland, California
A magnitude 5.5 earthquake 2.0 miles deep, centred in Los Angeles County. The 182nd strongest in California’s record since 1900, and the strongest within 50 miles since a magnitude 5.9 on October 1, 1987. 86 aftershocks of magnitude 2.5 or more followed within 30 days.
Watch the sequence unfoldMagnitude 5.5 · February 28, 1990
How the ground moved
Every recorded earthquake in the sequence, in order, from the foreshocks to a month after.
The earthquake
- Magnitude
- 5.5
- local magnitude (ml)
- Depth
- 2.0 mi
- 3.3 km below the surface
- Local time
- Wednesday, February 28, 1990
- 15:43 PST; 23:43 UTC
- In California’s record
- 182nd
- strongest of 97,065 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event ci1053635 (“The 1990 Upland, 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.
86
Aftershocks in 30 days
4.7
Largest aftershock, Mar 1, 1990
50
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.
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 · 8.7 mi
- Riverside CountyCA · 11.0 mi
- Orange CountyCA · 14.5 mi
- San Diego CountyCA · 45.4 mi
- Kern CountyCA · 47.0 mi
Cities, largest first
- Los AngelesCA · 41.7 mi
- Long BeachCA · 36.9 mi
- AnaheimCA · 20.2 mi
- RiversideCA · 22.5 mi
- IrvineCA · 32.5 mi
- Santa AnaCA · 30.1 mi
- Santa ClaritaCA · 49.6 mi
- San BernardinoCA · 23.0 mi
- FontanaCA · 13.6 mi
- Moreno ValleyCA · 32.0 mi
- Huntington BeachCA · 35.5 mi
- GlendaleCA · 31.5 mi
Earthquakes around the epicentre
1,357 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
- February 9, 1971M6.6
- March 10, 1933M6.4
- July 22, 1923M6.2
- May 15, 1910M6.0
- October 1, 1987M5.9
- February 9, 1971M5.8
- February 9, 1971M5.8
- September 19, 1907M5.3
- August 4, 1927M5.3
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.