Don't skim on a quality glass tank (forget the Petco off-the-shelf specials) and well-crossbraced stand with a sturdy bottom rim, and you will withstand most earthquakes. Securing your rock carefully (drill and use acrylic rods, etc.) will prevent many accidents.
Even a "medium" earthquake like Northridge took out a lot of glass tanks where acrylic survived. But also plenty of folks with glass made it through okay, for various reasons up to and including well-built stands with heavy sumps under them to minimize the top-heaviness.
Carefully shielding your electrical and using GFCIs is more important, because electricity happens all the time and earthquakes rarely do. A small backup generator or a big beefy backup battery are critical for those rare emergency occasions, and I'm afraid electricity is not so reliable as it used to be here.
Of course, I went with acrylic anyway. I'm paranoid. It doesn't take much to bust a glass tank seam.