The Fort Tejon earthquake occurred at about 8:20 AM (Pacific time) on January 9, 1857. It ruptured the San Andreas Fault for a length of about 225 miles (350 kilometers), between Parkfield and Wrightwood. The average slip along the fault was 4.5 meters (15 feet), and a maximum offset of 9 meters (30 feet) was recorded in the Carrizo Plain area. The amount of fault slip gives this earthquake a moment magnitude of 7.9, comparable to that of the 1906 San Francisco earthquake. Based on the (uncertain) distribution of foreshocks for this earthquake, it is assumed that the beginning of the fault rupture (the epicenter) was in the area between Parkfield and Cholame, about 60 miles northwest. Nevertheless, it is usually called the "Fort Tejon" earthquake because this was the location of the greatest damage, most of the area being unpopulated at the time.
By kkeps @ 2010-01-16 17:15:10