Earthquakes in California are common occurrences as the state is located on the San Andreas Fault, which cuts across California and forms the tectonic boundary between the Pacific and the North American Plate. There are many thousands of small earthquakes per year, most of them are so small that they are not felt. California’s complex and interesting landscape can be attributed to the network of faulting that runs underneath the state. The earliest reported earthquake in California was felt in 1769 by the Portola expedition about 30 miles southeast of Los Angeles, probably near the San Andreas Fault.
California has hundreds of active faults located throughout the state that are capable of producing large earthquakes. The most active fault is the San Jacinto Fault in Southern California, which has produced large events on a regular basis throughout recent history. The Mendocino Triple Junction located offshore of Northern California is also very active, producing several earthquakes above magnitude 7 throughout history. Northern California is also subject to megathrust earthquakes on the Cascadia subduction zone (extending north from Mendocino), such as the 1700 Cascadia earthquake, magnitude of approximately. The town of Parkfield in central California is located on a section of the San Andreas Fault that produces an earthquake of about magnitude 6 every 20–30 years on average in 1857, 1881, 1901, 1922, 1934, 1966 and 2004.
The largest recorded earthquake in California was the 1857 Fort Tejon earthquake, with an estimated magnitude of 8.0. This earthquake ruptured the San Andreas Fault from Parkfield to Wrightwood, a distance of 225 miles (350 km). The most destructive earthquake to date was the 7.9 magnitude 1906 San Francisco earthquake, in which over 3000 people perished in the earthquake and the fires that followed. The 1906 quake ruptured the northern segment of the San Andreas Fault for 296 miles (477 km), from San Juan Bautista to near Cape Mendocino in the north. More recently, the 1989 Loma Prieta earthquake, which affected the San Francisco bay area and the 1994 Northridge earthquake which hit the Greater Los Angeles area, caused widespread damage and deaths in their respective regions http://www.youtube.com/watch?v=Msgg3dGdmk4