Hey Pomp,
Just to throw in my $2 (things are more expensive in Cali, so I hear), maybe you need to go another route than X10 on this one. How often does "the big one" affect the power?
The gang here has come up with lots of neat actuators for the "Pomprocker Earthquake Dectection System", why not put a couple of these on some self contained battery lights for safety's sake. Keep the HA system too, just make it a little redundant.
Just a thought.
(I've never lived through a major quake, but we do get tornadoes. I might just build some of these myself, as I'm not sure that if my house landed in Oz, the power grid would be 120/240, 60Hz.)