Insurance is they only way really. Depending on the type of earthquake your experiencing, rolling or jarring, your tanks may survive or not. If you have a tank with a wider footprint as oppose to a taller show tank profile it might not topple over. I was standing about 10 feet away from a 10k gal salt water tank during one of the Northridge earthquake after shocks and saw the tank jump about a good 8" up and then settle back down(it had a metal stand) without any major damage. Now even if your aquarium survives the earthquake depending on how you have your tanked plumbed, the bulkhead or pvc could shear off the tank resulting in a major puddle of water. Just remember, that insurance will not cover the livestock you have in the tank.