The earthquake and tsunami weren't the coupled failures they were talking about. It was the loss of external power and backup generators. This is what they didn't expect, because it is hard to predict the probability of an event big enough to trigger these two things failing at the same time.
Yes, it's indeed hard to predict an earthquake to take out the external power and the subsequent tsunami to take out the backup generators on a coastline facility.
How big of a tsunami was required? How big of a earthquake would be required to generate such a wave? How much water would be needed to reach the facility? How much to damage it? What about damaging backups?
Sarcasm aside, it is easy to predict that the facility would be at risk for an earthquake/tsunami combo. The hard part is to predict how much of one to prepapre for. Remember, even in this neck of the woods, the was a quake of historic proportions.
"The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, or more rarely by meteorites and nuclear tests."
Like the previous gentleman stated. Better advisers?
Are you shitting me? This is Japan. Earthquakes happen very often and it's well known even by common people that they are closely followed by tsunamis. The fact that they didn't go together in any of the scenarios is mindblowing.
[1] http://en.wikipedia.org/wiki/List_of_earthquakes_in_Japan
[2] http://en.wikipedia.org/wiki/Fukushima_I_Nuclear_Power_Plant...