[Orion78]

It is not that far fetched to suggest that movement of either the North American Plate or the Pacific Plate could result in both increased earthquake along the San Andreas and movement of magma to the surface in the Cascades. Both volcanoes and earthquakes are a result of tectonic activity.

[MineralMan]

"It is not that far fetched to suggest that movement of either the North American Plate or the Pacific Plate could result in both increased earthquake along the San Andreas and movement of magma to the surface in the Cascades. Both volcanoes and earthquakes are a result of tectonic activity."

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The plates are always in motion. You aren't quite getting this. There's no connection between the faults in SoCal and the Cascades, other than them being on the same continent. They're seismically not related. You can look all this stuff up on the web. I don't have time to dig it up for you.

[MineralMan]

Here's a graphic for you: Notice that the plate off Oregon and Washington is neither the Pacific or North American plate. The Juan de Fuca plate is the remnant of a larger plate, and is being pushed UNDER the North American plate. It's not really influenced that much by the San Andreas fault system. Subduction is not taking place at this time along the California junction of the Pacific and North American plates. What happens in California has virtually no effect on anything in the Cascades, which is a volcanic zone due to the subduction of the Juan de Fuca plate.

[MineralMan]

Here's another graphic, which shows the relative motions of the west coast of the US. Note that the boundary between the Pacific Plate and the North American plate is not a subduction area. The San Andreas Fault is a transform fault, meaning that the boundary of the two plates is a zone where one plate is sliding against the other. North of Mendocino, you find the subduction of the Juan de Fuca plate, which leads to the formation of the Cascades, extending down clear to Mt. Lassen in CA. The Los Angeles area is actually atop the Pacific Plate, while the rest of CA is on the North American plate. For a very, very long time, the Pacific Plate has been moving northwards, which is why CA can't fall off the map. I hope this helps.