6.3 Earthquake off coast of San Diego


Tectonic Summary

The December 14, 2012 M 6.3 earthquake 250 km southwest of Avalon, California occurred as a result of shallow normal faulting within the oceanic lithosphere of the Pacific plate.

This event is located some 400-450 km west-southwest of the plate boundary between the Pacific and North America plates – the San Andreas fault system in southern California – and is not associated with that fault system.

Instead, this earthquake represents intraplate faulting along northeast-southwest trending normal faults within the crust of the Pacific plate, just to the west of California’s continental shelf.

The causative fault is not known at this time.


At the location of this event, the Pacific plate moves to the northwest with respect to the North America plate at a velocity of approximately 54 mm/yr.While the broad region surrounding the December 14, 2012 event experiences frequent earthquakes along the San Andreas and associated faults in southern California, the area offshore and within 250 km of this earthquake has not hosted any events greater than M 6 over the past 40 years.


The largest nearby earthquake was a M 5.1 event 200 km to the northeast in June of 2004, 80 km west of the border between the US and Baja California. A M 3.3 earthquake struck approximately 35 km to the northeast in April 1981, representing the closest event in the USGS earthquake catalog.