Here, in Mississippi, we occasionally get small, localized quakes, but in the event my general area gets hit by a major earthquake, it will likely be from the New Madrid fault, and I suspect our aquariums would be far down our list of worries if that happens. The last time it slipped--centered near the Mississippi River a bit north of Memphis--it is said that it caused church bells to ring in Boston, Massachusetts, and opened a hole so large that the Mississippi River flowed backwards for two whole days in filling it up! large parcels of land were raised or lowered ~100 feet and rivers changed course within seconds (one woman was in her outhouse at the time, and when she came out, there was a small river between her and her house, which had previously been on the same side of the river! lol). All this is well documented, and the recorded anecdotes are a very interesting read. The only reason there wasn't a major loss of life (people-wise, anyway) is because the area was so sparsely populated (not many heavily constructed, "modern" buildings, anyway). Yeah, I don't think our aquariums are going to be our biggest problem around these parts if and when "The Big One" hits here.
However, they are always discovering previously unknown faults here--only due to the "surprise" earthquakes--and seismology isn't really very focused on the southeast USA region, so who knows what can happen? Especially if they start "fracking" around here, like they're doing in Oklahoma, and causing earthquakes.
If you live in an earthquake-prone zone, I guess the best you could do would be to anchor the stand to the floor and/or wall. Smaller tanks would be at more of a risk, because their center of gravity is not supported by a larger footprint like it is with a bigger tank; think of the ease at which a 10 gallon on a stand can be tipped over in comparison to a 55 gallon or, better yet, a tank with an 18" depth (front to back). The weight of the water has to be shifted sideways (or more easily front-to-back) to tip the setup, and smaller tanks have a shorter distance for the water to travel to reach the tipping point, Waves would likely be induced by a side-shifting earthquake, but by anchoring the stand to the floor, you shorten the pivot-point (and thus the leverage of the weight shift) from the distance between the tank's center of gravity and the floor (typically 30"+), to the distance between the tank's center of gravity and the top of the stand (5" to 12", usually), so the whole setup is less likely to tip over. Of course, this assumes that the stand itself is sturdily built to begin with and wouldn't collapse under the sideways shift of weight.
However, I hope none of us ever have to deal with the actual reality and aftermath of an earthquake.
"May the Fish be with you."