Despite their weight, aquariums are not earthquake-proof. Water sloshing back and forth can bring an entire tank down to the floor, flooding the space and scattering broken glass, not to mention putting your fish in imminent peril. You can reduce -- but not eliminate -- the risk of earthquake damage to aquariums.
Secure the Stand
Securing an aquarium stand may not keep the fixture from falling apart during an earthquake, but doing so will prevent it from moving if it does not disintegrate. Securing the stand requires similar tools and techniques to securing any large piece of furniture. Get nylon moving straps or earthquake straps, washers or grommets and screws at least 2 inches long. Find a stud in the wall behind the stand. Drill pilot holes into both the stud and the back of the aquarium stand. Then, using either a drill or a screwdriver, affix the straps to both the stand and the stud, with 1 inch of play to accommodate shaking without snapping the straps. Use two straps to distribute the weight. Also, use either a washer or a grommet around your screws to avoid tearing the straps.
Securing the Tank
You have two ways to secure an aquarium. You can secure it to the stand or to the studs of the wall where it sits on the secured stand. Use a stand with a larger footprint than the tank itself. Using screw-in clips, you can secure the base of the aquarium against its stand. To secure the tank to the wall, secure Velcro earthquake straps to studs, then wipe the back of the aquarium with rubbing alcohol and allow it to air dry. Then affix industrial Velcro strips to the back of the tank. Use two Velcro-secured earthquake straps to distribute the weight, and allow an inch of give.
Tank Materials
Some aquarium materials better resist stress than others. For example, glass aquariums are prone to cracking or shattering when subjected to stress. Acrylic better resists structural stress but has drawbacks. An acrylic tank typically costs more, and it is easier to scratch when cleaning. However, acrylic's better resistance to breaking makes it the right choice in an earthquake zone.
Positioning the Tank
You can position a fish tank to mitigate risk of earthquake damage. The California Emergency Management Agency suggests positioning aquariums away from doors and exit paths. Additionally, placing aquarium on the floor instead of on a stand greatly reduces the chance of earthquake damage. However, this does make it harder to look at your fish and makes maintenance more difficult since it is harder to get a siphon started the lower the tank sits.