I also live in Cali and was somewhat concerned about earthquakes as well, to the point I was thinking about bracing the tank to the wall or whatnot.
I have a 46gal glass bowfront, and after filling it up, tried moving it around a bit to see how easily the tank would slide off the stand, how much shear force would be necessary to jostle it enough to really push it over, and came to this conclusion:
If an earthquake were to occur, I'd undoubtedly have water all over the place from the sloshing around. It would have to be a pretty big quake (and not one of the rolling ones, but the sharp jerky ones) to displace the tank enough so that it would crash onto the floor. Big enough, that I think I'd be concerned with a lot more in my apartment (big TV, structural integrity of the building, etc.) than with potentially losing a tank and a bunch of water seeping into the carpet (which again, would happen anyways, just not as much water).
Lastly, looking at glass vs. acrylic... If the tank fell down, you'd likely lose everything (fish, water, etc) anyways, the tank itself is pretty cheap to replace. Go with what you like best in terms of asthetics, cleanability, etc.