 The Mendocino Fault is seismically active with mostly small and moderate earthquakes , but the largest event that was unequivocally associated with the fault was the M6.9 earthquake on September 1 , 1994 at 125 @.@ 8 W longitude . Aftershocks of that event with corresponding dextral strike @-@ slip focal mechanisms occurred farther to the east and close to the Mendocino Triple Junction . Another large event ( 7 @.@ 3 – 7 @.@ 6 ) occurred on January 31 , 1922 ( with an aftershock of M7 + the next day ) but the sources of these shocks could not be determined with any precision as the first seismographs did not arrive in the area until 1932 . Due to their offshore epicenters all of these events caused little damage though were felt across a broad area . Previous Gorda plate events include the July 13 and August 17 , 1991 shocks of 6 @.@ 8 and 7 @.@ 1 and the M7.3 event on November 10 , 1980 west of Arcata . 
