r - The Hong Kong Polytechnic University

INADEQUACY OF TSUNAMI MITIGATION STRATEGIES
Tsunami Barriers
Although the 2011 Tohoku tsunami is not the first tsunami occurred in this region, the tsunami hazard along the
coastline of Iwate and Miyagi Prefectures is clearly underestimated and inadequate mitigation strategies had
been employed. According to the records compiled by the Japan Meteorological Agency, tsunami induced by
submarine earthquake in the “Off Miyagi” and “Off Sanriku” sources (source zone of the 2011 Tohoku
earthquake) had caused fatality of 1,000 in 869 (M~8.3), 50 in 1,611 (M~ 8.1), 44 in 1973 (M~8.2), 27,122 in
1861 (M~7.4), 3,000 in 1915 (M~7.5), and 28 in 1936 (M~7.4). In 1896, a M ~7.6 earthquake had created
tsunami waves as high as 38 m, killing 22,000. In 1933, a massive earthquake of M ~ 8.6 produced tsunami
waves as high as 29 m on the Sanriku coast and caused more than 3,000 deaths. Yet, the countermeasures
against tsunami are clearly not enough. For example, all tsunami barriers built along the coastline of Miyagi
and Iwate Prefecture were not high enough to stop the tsunami surges and thus actually provided a false sense of
security along the coastal cities. For example, Figure 4 shows the tsunami barrier built along the coastline of
Miyako City which is clearly not high enough in stopping the tsunami. Another example is the tsunami barrier
shown on the left of Figure 5 at Taro, Miyagi Prefecture. The devastation in the Taro City after the tsunami is
shown on the right of Figure 5.
Figure 4 Over flowing of the tsunami surges over the barrier wall at Miyako City.
Figure 5 Tsunami barrier at Taro and devastation at the city after the 2011 Tohoku tsunami
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