A "Big One" has happened on numerous occasions over the last few decades and century......and Cali is still there standing there as prosperous as ever
Earthquakes are so common there EQ proof building codes are severely enforced and architects and engineers have advanced building and civil infrastructure design to the point that those hoping for another SF 1906 type disaster will ALWAYS be disappointed.
Of course ANYTHING can happen as no one controls mother nature.
NYC, Philly, D.C. and Boston can be hit by a Hurricane. Phoenix can be buried in a dust storm, New Orleans can disappear completely under flood waters....and there's the always popular giant dinosaur killing meteor striking again...
Odds are that you'll be struck by lightning ...before Cali disappears or is badly crippled by an earthquake ...or Any of those other "It could happen"
type earth shattering natural disasters happen that TV documentaries try to use to scare you with.
You want something to fear that is really going to happen? Fear Global warming.
That is the real developing global disaster that will with 100% certainty wreak havoc worldwide like you or your children have never seen before.
I'm not going to argue with anyone about it ...because you'd have to be an idiot to ignore the facts of its existence...and I don't argue with idiots.
For some ungodly reason it's been politicized ....on an issue that even the Oil Companies agree is happening....now that to me is amazing
So believe whatever you want ....but know this ...your beliefs won't change the facts