I think those areas you are speaking about are subduction areas - we don't have subduction (currently) along our coast so the possibility of us sinking is pretty remote - there are some other causes of subsidence like between 2 strike-slip faults the area between can be stretched/widened and subsequently subside (Salton sea area is a good example) - or like in Long Beach's case when too much oil is pumped out and the ground sinks - or the central valley when too much water is pumped out and it sank.

But we currently don't have subduction going on so its unlikely we will 'fall into the ocean' - we will have norhtern california neighbors someday :-)

Canie