Vol.5 No.4 2013

Research paper : Reconstruction of the 869 Jogan tsunami and lessons from the 2011 Tohoku earthquake (Y. Okamura)−246−Synthesiology - English edition Vol.5 No.4 (2013) accuracy of tsunami magnitude prediction can be improved by applying this result of tsunami deposit research in other ocean areas.The Tohoku-oki Earthquake proved that the tsunami deposits were highly reliable evidences of the past giant tsunamis, and these deposits must be taken as important warnings from nature. On the other hand, there were some problems for estimation of tsunami magnitude.6 Announcing the earthquake study to societyThere was a common preconception that earthquakes would not strike the Kansai district before the 1995 Kobe Earthquake, but active fault researchers clarified that Mt. Rokko had been uplifting due to fault activity and that there was a possibility of a major earthquake in Kobe. The knowledge of such researchers were not utilized in the regional disaster prevention. To utilize the research results of earthquake research in the earthquake disaster prevention in society, it was determined that the government must evaluate the research results objectively and then provide this information to society as reliable crucial information important for disaster prevention. The Earthquake Headquarters was established to achieve this mission (Fig. 9).After the 1995 Kobe Earthquake, the danger of active faults became widely known, the research to clarify the activity history was conducted, and the active fault evaluation was published by the Earthquake Headquarters. The subduction zone earthquakes were evaluated based mainly on historical records. Through such evaluation and publication of the dangers of earthquake by the Earthquake Headquarters, the local governments and society became aware of the danger and had to take action for disaster mitigation.The research results of the Jogan Earthquake discussed earlier were submitted by AIST to the Earthquake Headquarters in the spring of 2010, and the headquarters conducted evaluations for about one year, for earthquakes along the entire Japan Trench. If the Tohoku-oki Earthquake did not occur, the evaluation of the Jogan Earthquake would have been announced in April 2011. Since it would take some time to prepare for the disaster prevention measures, it is unknown how it could have helped the disaster mitigation. At least it would have been an opportunity for many people to know the possibility that a giant tsunami might strike the Ishinomaki, Sendai, and the Fukushima coasts.We are regrettable that the research results were not announced from the Earthquake Headquarters before the earthquake, and we are still thinking that the information might have mitigated the damage to some degree. At the same time, we had been trying to inform others of our research Fig. 6 Example of calculation of the inundation area based on the Jogan tsunami source model (edited from References [17] and [18])The inundation zones of Ishinomaki Plain (top) and Sendai Plain (bottom) based on models 5, 6, 10, and 11 of Fig. 5. Ultimately model 10 (second from right) was selected as the Jogan model.Mw8.3Mw8.3Mw8.4Mw8.4Mw8.4Mw8.4Mw8.3Mw8.3Sendai PlainIshinomaki PlainSlip 5 mMw8.3Slip 7 mMw8.4Model 5:d15L200W100u5Model 6:d31L200W100u5Model 10:d15L200W100u7Model 11:d31L200W100u7


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