Jerry,
Yes, that is my opinion as well. However, the brackets were manufactured and (presumably tested/listed) for this specific purpose, so...
However, the bracket is attached at one point only, which could allow the tank to rotate around that point in an earthquake. It seems to me that this would give the tank leverage over the attachment point, which would be more likely to fail. Straps are anchored in two locations, which if done properly (they rarely are) would limit lateral movement.
Thanks for the response, even if it is from hurricane country and not earthquake country.
