Earthquake predictions and statistics: A 98 percent chance within 30 years and a 70 percent chance within four years mean the same thing
Jan 30, 2012 9:10pm
This puts the recent news that there is a 70% chance of a magnitude 7 earthquake hitting Tokyo within the next 4 years into perspective. (parts from Mainichi Japan) Last week Tokyoites were shocked by news indicating there was a 70 percent chance of a magnitude 7-level earthquake hitting the capital within four years. The news caused a stir because it was based on projections by the authoritative Earthquake Research Institute (ERI) at the University of Tokyo. The facts behind the report are very interesting. The initial report on the likelihood of a major quake appeared in The Yomiuri Shimbun's Jan. 23 morning editions. In a front-page exclusive, the daily reported the news with the banner headline: "70% chance of magnitude-7 level Tokyo earthquake within 4 yrs.'' The Nikkei, The Tokyo Shimbun and the Mainichi Shimbun followed suit in their evening editions and The Asahi Shimbun and The Sankei Shimbun caught up with them in their Jan. 24 editions. All trailing dailies had almost identical headlines. TV stations quickly reported the news through their news departments as well as in other programs. Overwhelmed by a barrage of reports by news organizations, the ERI published a special explanation online to account for the reasons behind the Yomiuri report. The fact is, the ERI's study team had reported its predictions at an open forum last fall, and they were covered by the mass media. Looking back, the Mainichi Shimbun reported in its Sept. 17, 2011 editions that there was a 98 percent chance of a magnitude 7-level earthquake striking the metropolitan region within 30 years. According to the ERI, a 98 percent chance within 30 years and a 70 percent chance within four years mean the same thing. But human beings, as they are, take the 30-year span lightly and are surprised by the four-year timeline. The Yomiuri keenly restructured the publicized data and emphasized the period "within four years," causing a big public reaction and forcing other news outlets to follow suit. Currently there is a run on earthquake preparedness goods. Also, it should be pointed out that a magnitude-7 quake's energy is one thousandth of the magnitude-9 Great East Japan Earthquake last March 11. Info from: http://mdn.mainichi.jp/perspectives/news/20120130p2a00m0na002000c.html
