Misunderstood Lessons From the 2011 Great East-Japan Earthquake Tsunami Disaster

Abstract eng:
At 14:46 (local time) on March 11th, 2011, an earthquake with moment magnitude 9.0 occurred off the shore of the Sanriku area in the Tohoku (North-East) Region of Japan. It was followed by a “Mega Tsunami” which hit deeply indented coastal areas and brought extensive and devastating damage to many cities, towns and villages. These areas have been historically attacked by large tsunamis, such as the 1896 Meiji-Sanriku, 1933 Showa-Sanriku, and 1960 Chili Earthquake Tsunamis and based on these experiences, people in affected areas have been promoting preparation of both structural and non-structural countermeasures against tsunami. It had been reported that this area had literally the highest tsunami disaster countermeasures in the world. The breakwater constructed at the mouth of Kamaishi Port, which was reported in the World Guinness Records and the tsunami levee with 10 m elevation called Taro’s great wall were typical examples of such structural countermeasures. However, the 2011 Tsunami exceeded the height of these structures and attacked inland, and caused devastating damage including over 18 thousand fatalities. Mass media have reported that tsunami disaster countermeasures had limited effects and could not reduce the damage despite the fact that these measures were prepared by spending a lot of money and time, and many people believed such reports. In this paper, I will prove such reports by mass media and lessons that many people believed to have learned from the disaster were not correct based on the quantitative analysis. And I will introduce positive and negative effects of both structural and non-structural measures. Following is one of the examples that is misunderstood by the general public. At the time of the earthquake, there were approximately 620 thousand people were in all areas inundated by the 2011 Tsunami. Among them, 18 thousand were killed which is 3 % of the total population. While it is important to verify the cause of fatalities and find solutions for them, it is also important to acknowledge that 97% of the people who were in the tsunami inundated areas were saved by the pre-event countermeasures that were in place. Survivors’ ratio of 97 % is very high compared to that of other massive tsunami disasters in the past worldwide. Unless we emphasize the importance and effects of pre-event countermeasures, the general public may underestimate their effects and easily forget their importance. The highest ratio of fatalities in only tsunami inundated area was 12.8 % of Rikuzen-takata City and that in whole municipality area was 9.46 % of Onagawa Town. These ratios are much smaller compared to the values in the past in areas that did not have well established countermeasures. For example, the fatality ratio was 32.7 % in Unosuma Village, 53.9 % in Kamaishi Ttown, and 66.4 % in Toni Village in case of the 1896 Meiji-Sanriku Tsunami disaster when the population of Japan was 42 million, one third of the current population and 22 thousand people were killed. The fatality ratios of Taro when compared among three disasters in 1896, 1933 Showa-Sanriku, and 2011 Great East-Japan Tsunami disasters, were 83.1%, 32.5 %, and 3.9 %, respectively. This is a proof that people could reduce the damage drastically by well-established pre-event countermeasures.

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