The offshore region is the site of the Mendocino Triple Junction, where the Gorda, Pacific and North American tectonic plates meet just north of the terminus of the San Andreas Fault.

In April 1992, a 7.2-magnitude quake, followed by 6.5 and 6.7 shocks, violently shook the coast 30 miles southwest of Eureka, causing more than 100 injuries and severe damage in several towns, including Ferndale and Petrolia.

In November 1980, a 7.2-magnitude quake centered just off the coast caused widespread damage around Eureka, including the partial collapse of a freeway overpass south of Eureka.

Mendocino Triple JunctionMendocino Triple Junction

6.8 Quake Shakes Northern California Coast; No Tsunami Threat