When I lived in SD, I had a neighbor that worked for the US Geological Service. He did an assessment of my home (tanks and furniture) compared to the direction of the local fault lines and calculated directions of tremors if and when they occur. He told me how to reinforce/anchor my tall furniture, aquarium stands, etc. He suggested that I caddy-corner my 90 show tank so tremors wouldn't rock the tank over. I didn't get to it before a tremor (after the Northgate quake) nearly tipped the tank over. My roommate saw the tank rocking and held it until the tremor passed. We made quick work of draining and turning the tank 45 degrees, bracing the stand legs to the floor slab, and adding metal brackets from the top of the stand to the wall studs.
I've since always had a survey done at any new address in CA. I'd recommend doing so. If it's not affordable, at the very least, brace all tank stands to make them safer in the event of a quake. Bracing all tall furniture (book cases, china cabinets, large TV stands, display cabinets, etc.) would also make good sense.