Molten Salt Thorium Reactors are earthquake safe. Thorium reactors have a very simple and compact design where gravity is the only thing needed to stop the nuclear reaction. Conventional nuclear reactors depend on external power to shut down after a SCRAM, where poison rods fall down to halt the reaction. The next figure shows the concept of a Thorium reactor.
The idea is to empty the fissile U-233 core through gravity alone. All that is needed is a melt-plug that is constantly cooled by cold air. In an earthquake or complete electric failure the cold air flow automatically shuts off, and since the fuel is already molten, it will melt the plug, and the molten fluid will run down into channels like pig-iron into heat exchangers that absorb the residual heat.
As we can see the reactor hardened structure is compact, and can be completely earthquake and tsunami proof. What can be sheared off are the steam pipes and external power, but even then the reactor shutdown will be complete safe without any additional power.
One of the advantages of the LFTR reactor is that the fissile compartment is always kept just above critical point for needed power delivery. This means, once it starts draining, the fission process ends immediately. The only nuclear reaction remaining is that the Protactinium generated in the fertile blanket and separator gets converted to U-233 over time, but the amounts are so small that it is always in the safe range.
Len Bilén's blog, a blog about faith, politics and the environment. 