The April 8, 1961 earthquake
M5.9near Tres Pinos, California
A magnitude 5.9 earthquake 7.5 miles deep, centred in San Benito County. The 100th strongest in California’s record since 1900, and the strongest within 50 miles since a magnitude 6.5 on July 1, 1911. 1 aftershock of magnitude 2.5 or more followed within 30 days.
The earthquake
- Magnitude
- 5.9
- moment magnitude (mw)
- Depth
- 7.5 mi
- 12.0 km below the surface
- Local time
- Saturday, April 8, 1961
- 23:23 PST; 07:23 UTC on Apr 9, 1961
- In California’s record
- 100th
- strongest of 97,065 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event iscgem876374 (“10 km SE of Tres Pinos, California”). 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.
1
Aftershocks in 30 days
5.5
Largest aftershock, Apr 9, 1961 · its page
1
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
- San Benito CountyCA · inside
- Merced CountyCA · 8.5 mi
- Monterey CountyCA · 9.2 mi
- Santa Clara CountyCA · 15.8 mi
- Fresno CountyCA · 16.8 mi
- Santa Cruz CountyCA · 23.0 mi
- Stanislaus CountyCA · 27.8 mi
- Madera CountyCA · 42.6 mi
Cities, largest first
- SalinasCA · 23.0 mi
- Santa CruzCA · 48.0 mi
- GilroyCA · 27.6 mi
- WatsonvilleCA · 33.2 mi
- Los BanosCA · 31.1 mi
- HollisterCA · 13.0 mi
- Morgan HillCA · 36.1 mi
- SeasideCA · 33.8 mi
- MontereyCA · 37.7 mi
- SoledadCA · 21.2 mi
- MarinaCA · 31.6 mi
- GreenfieldCA · 28.2 mi
Earthquakes around the epicentre
2,783 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
- July 1, 1911M6.5
- May 25, 1905M6.1
- June 11, 1903M6.1
- July 25, 1926M5.8
- March 10, 1910M5.8
- August 6, 1916M5.8
- December 31, 1910M5.7
- June 24, 1939M5.5
- March 2, 1959M5.3
- April 25, 1954M5.3
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.