Source: U.S. Geological Survey
See Richter Magnitude Scale for a description of the impact of various magnitude levels.
Also see:
-- The ShakeOut Scenario - What Could Happen
-- Know What To Do Before, During and After a Major Earthquake
-- Significant Earthquakes Impacting Los Angeles County.
Southern California is Overdue for a Major Earthquake
Geologists warn us that Southern California is overdue for a major and possibly catastrophic earthquake along the San Andreas Fault. At magnitude 7.8 or higher, it will be a beast.