There are 104 licensed Nuclear reactors currently operating in US. Some are located in high risk areas of earthquakes, making them more vulnerable to damage.
If any slight earth quake disturbs the area of the nuclear reactor the chain reaction of nuclear reactor might not be controlled making the surrounding area dangerous for life.
The 10 Us nuclear reactor sites with the highest risk of suffering core damage from earth quake, as accessed by Nuclear Regulatory Commission. the list is based on 2008 geological data, taking to account the design standards used at each plant and type of rock or soil built upon.