If historical records had been more complete, and if discrepancies between data had been picked up, we might have been alert to the danger of a magnitude-9 earthquake hitting Tohoku, even though such an event was not foreseen by the Japanese government. In 2002, the Headquarters for Earthquake Research Promotion of the Japanese government released a long-term evaluation of the likelihood of subduction-zone earthquakes in the Tohoku region. It estimated an 80-90% probability that the area would have a large earthquake of magnitude 7.7-8.2 in the next 30 years. But the probability of a magnitude-9 earthquake affecting a 400-500-kilometre area was not specifically mentioned. As a member of the working group involved in the evaluation, it is with great regret that I reflect on the causes of this failure.
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