A Magnitude 6.5 earthquake rattled the northern California coast on Thursday morning, swaying buildings in Humboldt County and releasing enough energy to be detectable in San Francisco. This was a signature earthquake of a part of California that may be as overlooked in earthquake science as it is in popular culture. Though the phrase "California earthquake" brings to mind San Francisco and Los Angeles – and rightly so due to the high seismic hazard in those urban centers – the region offshore Humboldt and Del Norte counties, called the Gorda deformation zone or the Gorda plate for short, is by far the largest producer of moderate and large earthquakes anywhere in California or on the West Coast. California has experienced six earthquakes of magnitude 7.0 or greater in the past 40 years; four of these have come from the Gorda plate and the faults that surround it, as well as several earthquakes of similar size to Thursday's M=6.5 event. Why are there so many earthquakes here The high