Very early in the morning of Oct 26th, a rather big earth quake has occurred in the Pacific ocean off Fukushima. The magnitude was 7.1. The quake has waken me up with the Richter scale rated 4 here. I could not fall asleep for a while even after a long lasting quake, reminding me of the big earthquake, had gone. An alarm for tsunami was published by an authority then. It seemed there had been a small tsunami observed near to the center of the earthquake.
The news told it had been caused by a mechanism of the outerrise. The ocean plate was freed from the friction with the continental plate by the big earthquake 2 years ago, so that the former could be lacerated pretty easily with the force pulling it under the continental plate. It is not negligible that a big earthquake of this type would occur in the near future.
The problem with this type of eathquake is that it could cause tsunami. The Pacific ocean off Fukushima is believed to be a center of such an earthquake. If a big tsunami would hit the damaged nuclear plant in Fukushima, there could be a further serious damage on it. The main concern is on the used fuels pooled at the 4th reactor. It still has a enormous amount of used/not used fuels. The pool is high in the damaged building. It could be very vulnerable to such a tsunami or an earthquake.
At present, they are struggling with the contaminated water and the influx of underground water into the reactors. They have not taken any measure against further tsunami to the damaged structures and/or the cooling system. If any big tsunami destroys them, the contamination of radioactivity would spreads all over Kanto plain including the metropolis of Tokyo. It is a matter of possibility. No one knows if it could happen or not. But the government should prepare for such a disaster. They should have learned that almost impossible thing could become possible from the disaster 2 years ago.