Eight foreshocks ( with a maximum magnitude of 3.8 ) preceded the main event . The first motion method was used to determine the focal mechanism of the mainshock . It was found to be dissimilar from the 1906 earthquake , and instead showed oblique movement on a steeply-dipping thrust fault , with the eastern side of the fault rising relative to the western side . The strike-slip component was minimal ; only about half as much as the thrust component
1906 earthquake
1906 San Francisco earthquake
1957 San Francisco earthquake