There seems to be some confusion here. Subduction occurs in a compressional regime where two plates collide. The land does not sink; the oceanic crust is pushed down under it. You do not get anything falling into the sea.

Subsidence happens in an extensional regime. One can get localised subsidence and extension in areas which are being heavily weighted by sedimentation; the Nile delta is one example, the North Sea is another closer to (my) home. This subsidence can be aseismic as well as seismic.

You are not getting any such activity offshore California so far as I'm aware.