A Japanese panel of seismologists knew about the risk of a major tsunami in northeastern Japan before disaster struck on March 11th. The group had put together a report in February and was planning to release it in April. NHK obtained a copy of the report drawn up by the government's Earthquake Research Committee. It focuses on quakes and tsunamis off the Pacific coastline of northeastern Japan.
The document includes the committee's analysis of an earthquake that is known to have struck the region more than 1,140 years ago. Citing recent studies, the report estimates that the ancient earthquake was caused when 3 sections of the seabed shifted simultaneously. It says the quake probably measured around Magnitude 8.3, triggering enormous tsunamis that flooded vast areas of Miyagi and Fukushima prefectures.
...snip...
One of the experts involved in the study says he regrets the committee's failure to warn of the risk as soon as it was discovered -- no matter how low the probability was.
http://www3.nhk.or.jp/daily/english/06_27.html In (probably) related news, the Prime Minister just asked Chubu Electric to shut down Hamaoka reactors #4&5 (1&2 are decomissioned and #3 was already shut down for inspection... #6 is still under construction) because of earthquake risks (it's also along the coast) until additional protections can be put in place.
From NHK - "The reactor complex sits directly above the projected focus of a magnitude-8 class earthquake that experts have long warned of."