The left-lateral strike-slip earthquake was the largest to occur in California since the 1952 Kern County earthquake . The mainshock ( which was described as a multiple-rupture , with four subevents in the initial 80 seconds ) and its aftershocks occurred on a northeast-trending fault that extended from near the Mendocino Fault to a point northwest of Eureka . Movement along the fault is due to a north-south compressional regime and the resulting intraplate deformation of the Gorda Plate . Previous events in this area were the January 1922 7.3 and the January 1923 7.2 shocks
1952 Kern County earthquake
1952 Kern County earthquake
1980 Eureka earthquake