The Japanese New Year started with an M7.0 earthquake centered at an island 600km south of Tokyo, but the quake was still strong enough to shake a very widespread area of northern Japan including Fukushima to a Level 4 of the Japanese local intensity scale of 7 levels.
Come January 2, Fukushima Prefecture’s official radiation monitoring system showed an unusual increase in cesium fallout from an ND (not detected) on January 1 to 432MBq/km2 on January 2. http://www.pref.fukushima.jp/j/koukabutsu9.pdf
This caught many radiation watchers’ attention so they started to tweet about it, and some of them contacted Professor Takeda, a nuclear scientist of Chubu University, who took the matter seriously and started to study about the general trend and possible causes. Although getting involved with researching the situation, Professor Takeda has said that he will give more details a few days later (this info as of January 7).
Especially on January 5 and 6 the Japanese portion of Twitter was buzzing with traffic on this subject. An Arnie Gundersen video advicing people to flee in case Dai-ichi Reactor 4 collapses was retweeted, and some people were saying that they were so worried that they did not feel like going to work. The information that Iwaki residents recently received new iodine tablets because the shelf dates of earlier distributed tablets had expired, was also taken out of context to mean that some new nuclear event was possibly unfolding.
Cesium fallout was also recorded in Chiba: http://www.jcac.or.jp/lib/senryo_lib/taiki_kouka.pdf
Even in Tokyo a minute amount of cesium was detected by a monitoring post in Koto Ward on January 5: http://www.sangyo-rodo.metro.tokyo.jp/whats-new/keisoku-0103.pdf
At TEPCO’s press conference on January 6 spokesperson Matsumoto said he has not been informed of the monitoring data in question, and that there was nothing unusual happening at Fukushima Dai-ichi. He said it was probably strong wind blowing up radioactive materials. Professor Nojiri also thinks it could be the wind stirring up the cesium, however Professor Makino says the amounts are larger than than the wind would be able to stir up, although the wind velocity reached max. 17.7m/s on Jan. 2~3.
The following data was compiled by Professor Okumura of Mie University from the monitoring posts around the Fukushima Dai-ichi and Dai-ni. The radiation levels were higher at several posts on January 2, but they do not indicate any emergency: http://oku.edu.mie-u.ac.jp/rad/
The following map shows where each monitoring post is located: http://www.atom-moc.pref.fukushima.jp/dynamic/C0008-PC.html
Professor Hayakawa of Gunma University commented that he thinks there is an element of panic in this particular instance.
It has come to my attention that on September 26, 2011 Fukushima Prefecture revised their official fallout data in the period from June 6, 2011 to July 30, 2011. The originally published fallout data was extremely low, while the revised fallout data shows a much higher level with large daily fluctuations.
The leftmost column of the following table shows the dates and timespan of the collection of fallout data. The middle column shows the published fallout data prior to revision, and the rightmost column shows the fallout data after revision: http://radioactivity.mext.go.jp/ja/monitoring_by_prefecture_fallout/2…
What I am implying here is that the recent furore of a “fallout spike” around January 2 may to some extent have been caused by the fact that many people had only watched the Fukushima Prefecture fallout data published prior to September 26.
The revised data shows wide fluctuations from less than 20MBq/km2 to 1340MBq/km2. When seen in this context the “fallout spike” on January 2, 2012 was not extraordinarily large.
Nevertheless. I feel that the recent situation should be watched and monitored to see if there could be an underlying longer-term cause of the recent increase in cesium fallout.
Note: For further fallout data by prefecture from March through December 2011, take a look at the following link: http://radioactivity.mext.go.jp/ja/monitoring_by_prefecture_fallout/index.html