The March 11, 2011 earthquake and tsunami caused massive destruction in Japan. Six nuclear reactors at the Fukushima Dai'ichi power plant became a significant cause for concern in the aftermath as the plant lost power and reactor cores started melting down. Both the earthquake and tsunami were much larger than predicted and caught everyone, including nuclear power plant designers, by surprise. How could the geologists who predicted these events have been so wrong?
The reactors had been designed to withstand an earthquake of magnitude 7.9. After all, in the entire 20th century, the maximum earthquake experienced in the region was magnitude 7.8. The Tohoku earthquake on March 11 was magnitude 9.0, releasing 45 times more energy than the reactor was designed to withstand. The tsunami wave height was also significantly underestimated. The Fukushima plant was designed to withstand a tsunami of 5.7 m height. Recent estimates put the Tohoku tsunami wave height at 14 m.
In the nuclear field, policy makers often demand predictions about Earth behavior: What's the largest earthquake that will occur at the site of a nuclear power plant? Will the nearby fault move? Is this a reasonably safe location to site a geologic repository for high- level radioactive waste? The advantage of these predictions is that they provide simple and straightforward parameters for policy decision-making. The disadvantage, as we now know, is that they can't be made with the necessary accuracy.