I work in the construction field and asked one of our engineers what would be the best foundation to build a structure on that would be as earthquake proof as possible. His answer:
Your foundation should be at least 3 feet in depth, reinforced with rebar that is placed in a double birdcage formation. This cage should be tied together where the rebar touches. Wrap the entire formation with strips of rebar that extend into holes that are sunk into the ground at a depth of 4'' x 4" by 6 ft. deep filled with more concrete. Use at least 8 holes, more if you want (4 corners and 1 additional at least on each side).
My best way to describe a double birdcage is to cup your hand with fingers gently curled up, do the same with the other hand, put the fingers from one hand into the palm of the other at cross angles and you kind of get the idea. The idea is that this foundation will float along with up and down shaking that comes with earthquakes. He said that in Japan, this is now the required code for all new construction.
Offered by Mary.