Here is a list of major earthquakes, in order of magnitude, that have struck California this century.
Today's earthquake near Los Angeles registered an estimated 6.0 on the Richter scale, a quake capable of causing severe damage. An earthquake measuring 7.0 on the Richter scale is a major quake, capable of widespread heavy damage; 8 is a great quake, capable of tremendous damage.
The Richter scale is a measure of ground motion as recorded on seismographs. Every increase of one number means a tenfold increase in magnitude. Thus a reading of 7.5 reflects an earthquake 10 times stronger than one of 6.5.
1906--San Francisco, 8.3.
1927--Offshore San Luis Obispo, 7.7.
1923--North Coast, 7.2.
1940--Imperial Valley, 6.7.