In my opinion the only way to make your home more earthquake proof is a better foundation, and that's not feasible after the fact. If you have a well built foundation, your home won't flex as much. My house was built on a bare-minimum foundation, and now I have a few doors that stick, and there are visible cracks in the paint in a few places. Several years ago we had a 6.0 earthquake about 30 miles away, and that's when our bathroom door started sticking.
The construction codes in Oklahoma are barely above dirt shack construction. We have a fair amount of vertical heave in our soil, we have near constant mild earthquakes, and our foundation requirements are minimal. We have the worst hail and our roofing code is bare minimum. There's no requirement for storm shelter, but people have been talking about adding it to the code.