There is an area of Long Beach that is notorious for subsidence - I think it was because the area was used as a dump some time back in history - lots of methane too - it's near the coastal area you talk about...Los Cerritos wetlands - it has nothing to do with tectonics...

and then there was all the oil being pumped out of the neighborhood... that also caused lots of land movement..

On Long Beach subsidence: http://cms.longbeach.gov/oil/subsidence.html

Canie