Washington’s Blog 
February 16, 2012
We have extensively documented the fact that engineers knew that Fukushima was built in an area which was highly-susceptible to giant earthquakes, and that it would fail in a large earthquake .
Unfortunately, Pandora’s Box may now have been opened.
Specifically, Japanese scientists have published a scientific paper  in European Geosciences Union’s journalSolid Earth  saying that the 9.0 earthquake last March has apparently “awakened” the Fukushima earthquake fault, making it likely that a large earthquake will occur this year right near the stricken nuclear complex.
Scientists studying readings from Japanese seismic sensors have determined that there have been 20 times more quakes in the 6 months after March 2011 than in previous 9 years.
As AFP notes :
The picture points to a low-activity fault that was jolted furiously into life by the big quake.
The seismic tomography also says that after March 11, the Iwaki fault suffered a dramatic change in the direction of stress from the overriding Okhotsk plate.
A shock change in horizontal thrust, helped by the weakening effect of the ascending fluids [which act like a lubricant], are what made this previously untroublesome fault to rip open, they theorise.
The worry is that something similar could happen at Fukushima because it shares a similar subterranean topography, although such an event is impossible to pinpoint in time, they say.
“There are a few active faults in the nuclear power plant area, and our results show the existence of similar structural anomalies under both the Iwaki and the Fukushima Daiichi areas,” Zhao said in a press release.
“Given that a large earthquake occurred in Iwaki not long ago, we think it is possible for a similarly strong earthquake to happen in Fukushima.”
Here is a graphic from the report:
The study area is indicated by a black box. The purple star shows the epicenter of the March 2011 earthquake, the red star the epicenter of the recent 7.0 Iwaki earthquake, the red square shows the Fukushima nuclear complex, and the black triangles indicate active volcanoes.
Scientists say that there is a 70% chance  of a magnitude 7.0 earthquake hitting Fukushima this year, and a 98% chance within the next 3 years.
The Biggest Danger: The Collapse of the Fuel Pools at Reactor 4
Given that nuclear expert Arnie Gundersen says that an earthquake of 7.0 or larger  could cause the entire fuel pool structure collapse, it is urgent that everything humanly possible is done to stabilize the structure housing the fuel pools at reactor number 4.
Tepco is doing some construction at the building … it is a race against time under very difficult circumstances, and hopefully Tepco will win.
As AP points out :
The structural integrity of the damaged Unit 4 reactor building has long been a major concern among experts because a collapse of its spent fuel cooling pool could cause a disaster worse than the three reactor meltdowns.
See this  for background on why the fuel pools are so dangerous.
Gundersen (who used to build spent fuel pools) explains that there is no protection surrounding the radioactive fuel in the pools. He warns that – if the fuel pools at reactor 4 collapse due to an earthquake – people should get out of Japan, and residents of the West Coast of America and Canada should shut all of their windows and stay inside for a while.