Vol.5 No.4 2013

Research paper : Reconstruction of the 869 Jogan tsunami and lessons from the 2011 Tohoku earthquake (Y. Okamura)−248−Synthesiology - English edition Vol.5 No.4 (2013) we took considerable time in conducting tsunami deposit research carefully. We estimated the minimum magnitude of the tsunami by the Jogan earthquake based on the detailed tsunami deposit research. Our study will lose reliability if we estimated too large an earthquake and tsunami without convincing evidences. After the 2011 earthquake, there was a period where we wondered whether this policy was correct. However, if we had announced a large tsunami prediction without presenting clear evidence to society before the earthquake, we think that our model would have been neglected. We believe our research policy was not wrong.The concern for earthquakes immediately rose after the tsunami devastated the coastal area of Tohoku on March 11, 2011. While the government and the local governments used to be reluctant to assume large earthquakes without sufficient evidence before the 2011 earthquake, they changed the policy to assume the worst possible earthquake and tsunami.[20] Under this policy, assumption of the worst possible earthquake and tsunami that may happen have been adopted, rather than an earthquake which had been confirmed in the past. The earthquake researches are demanded to determine the magnitude of the largest earthquake. It is not too much to say that the demand for earthquake research changed around 180 degrees. Unfortunately, current earth science cannot determine the largest earthquake reasonably. As a result, there are possibilities that unnecessarily large earthquakes and tsunamis may be assumed. The research to determine the appropriate maximum earthquakes is necessary.8 Future issuesThe Japanese society will be unable to recover from the shock of Tohoku-oki Earthquake for a while. Whatever size of earthquake and tsunami will be assumed in the future, we will not be freed from the fear of earthquakes and tsunamis. The disaster prevention measures to mitigate the damages from earthquakes and tsunamis must be steadily conducted to decrease the fear, but it is not easy to determine the appropriate measures against the large tsunamis. The sense of crisis over natural disaster must be sustained even after the disaster prevention measures are taken. Considering the role of the geology fields at AIST (Geological Survey of Japan), the most important missions are to conduct careful research of the past earthquakes, to clarify what earthquake occurred in which area, and to continue providing this information to society. In addition, it is necessary to show what is known and unknown about ancient earthquakes based on the current level of natural sciences. It is then necessary to consider how the measures should be taken as a society as a whole.For the research results of AIST to be utilized widely in society, I mentioned that we need a system in which the results are reevaluated and announced by the Earthquake Headquarters as an official organization. However, this alone does not ensure sufficient dissemination of information to the regional communities, and the process usually takes time. It is considered that AIST must directly provide detailed information to the local governments and communities about the information on which the evaluation of the Earthquake Headquarters is based and what are the issues, and at the same time actively exchange information. Moreover, we may consider information provision to local governments before the announcement of the Earthquake Headquarters. To conduct such information exchange, it is necessary to establish mutual trust by holding meetings with the prefectural and other local governments regularly.At the same time, it is necessary to design land use plans in Japan based upon an understanding of nature and the evaluation of various disasters. For better land use, comprehensive knowledge about the geological characteristics of the Japanese Archipelago needs to be provided. The Japanese have experienced various damages from natural disasters and have overcome them and built the prosperity today. For example, the technology of earthquake resistant structures of Japan is the most advanced in the world. However, it must be said that society as a whole is becoming vulnerable to natural disasters. One of the reasons may be that the people are becoming less knowledgeable about nature. By understanding the crustal movement in the Japanese Archipelago that occurred in the past tens of thousands of years based on geology, I hope people will become prepared against natural disasters. The mission of the geology field of AIST is to provide such information to society.AcknowledgementThe research of the Jogan Earthquake was conducted through the collaboration of the following researchers: Masanori Shishikura, Yuki Sawai, and Yuichi Namegaya, researchers Fig. 9 Role of the Earthquake HeadquartersThe Earthquake Headquarters or the Headquarters for Earthquake Research Promotion, MEXT, gathers information from the survey and research institutes for earthquakes, reevaluates the information, and announces the scale and probability of the earthquakes that may occur in the future.Announcement of the evaluationSubcommittee for Long-term Evaluation 2010Announcement in April 2011?Disaster prevention measures of Government, regional area, and societyUniversities, research institutes, etc.Master planSurvey & measurement planSurvey & measurement dataResearch productEarthquake Research CommitteePolicy CommitteeResearch project on Miyagi-oki Earthquake 2005-2009Earthquake Headquarters, MEXTResearchEvaluation by governmentPublicity


page 24