Petra,

That bit is ambiguous, they mean the Juan de Fuca plate extends down as far south as Cape Mendicino, not the North American plate.

"Seismic Society of North America" is the SSA, I presume.

I don't know what this means: "You can actually sit here and ride the movement through like on a surf board."

Why they are quoted as being able to predict a big earthquake is also a mystery, they are really saying the chatter can sometimes precede an aseismic slip episode, would could conceivably precede some earthquakes, either large or small.

In fact, the nature of the chatter is not clear. They may mean shallow volcanic harmonic tremor, or perhaps deeper (up to 40 km depth) tremor such as has been interpreted interpreted as moving magma when seen under Japan.

John