The USGS said that the epicenter of the earthquake was located off the coast of northern California, 12 kilometers (7.5 miles) southwest of the city of Ferndale.
A series of aftershocks of magnitude ranging from 2.5 to 4.6 was recorded in the area from 10:39 to 11:03 GMT, with their epicenter lying at a depth of 15.4 to 24.1 kilometers.
There has been no immediate information about casualties or destruction.