A magnitude 6.5 quake has struck offshore of northern California, about 25 miles offshore of Ferndale and Eureka, at 4:27 PST. It was apparently felt widely across the northern part of the state. Seven aftershocks in the range of 30-4.5 magnitude have followed the main shock so far. This area is quite close to the Triple Junction where three plates, the Gorda, Pacific and North American come together. The fault motions were primarily horizontal so a tsunami is not considered likely (and it would have hit onshore by now anyway). Andrew Alden at About.com:Geology provides a nice perspective of the quake, the biggest in the lower 48 states in a couple of years.
Update, 1/10: 23 aftershocks thus far, including three that exceeded magnitude 4. Some minor damage reports, in the form of fallen chimneys and broken windows. A nice history of seismicity in the region by the Berkeley Seismological Laboratory can be seen here.