Step 1: What an earthquake can do
See how the water heater just falls over?
You might be thinking that if there's a strong enough earthquake to tip over my water heater, I've probably got bigger issues. Perhaps true, but I don't want to add fire from broken gas lines and flood from broken water lines into the mix.
You'll note in the pictures, I've already installed a flexible gas line, and semi-flexible water lines. The water lines are ribbed copper pipes that have some flex to them.
Step 2: Get a strapping kit
Here's the kit: It's essentially some metal straps and fittings.
Step 3: Plan
Step 4: Mount the straps
Step 5: Supports behind the water heater
Step 6: Shove the support in place
Step 7: Tighten straps
Previously my water heater had some play; it now feels rock solid.
Step 8: Just in time!
It wasn't strong enough that the strapping was actually necessary, but made me feel really glad to have it complete.