Lessons Learned from the 2011 Great East Japan Tsunami: Performance of Tsunami Countermeasures, Coastal Buildings, and Tsunami Evacuation in Japan
0
Department of Civil Engineering, Ocean Engineering Research Center, Middle East Technical University
, Ankara,
Turkey
1
International Research Institute of Disaster Science, Tohoku University
, Sendai,
Japan
In 2011, Japan was hit by a tsunami that was generated by the greatest earthquake in its history. The first tsunami warning was announced 3 min after the earthquake, as is normal, but failed to estimate the actual tsunami height. Most of the structural countermeasures were not designed for the huge tsunami that was generated by the magnitude M = 9.0 earthquake; as a result, many were destroyed and did not stop the tsunami. These structures included breakwaters, seawalls, water gates, and control forests. In this paper we discuss the performance of these countermeasures, and the mechanisms by which they were damaged; we also discuss damage to residential houses, commercial and public buildings, and evacuation buildings. Some topics regarding tsunami awareness and mitigation are discussed. The failures of structural defenses are a reminder that structural (hard) measures alone were not sufficient to protect people and buildings from a major disaster such as this. These defenses might be able to reduce the impact but should be designed so that they can survive even if the tsunami flows over them. Coastal residents should also understand the function and limit of the hard measures. For this purpose, nonstructural (soft) measures, for example experience and awareness, are very important for promoting rapid evacuation in the event of a tsunami. An adequate communication system for tsunami warning messages and more evacuation shelters with evacuation routes in good condition might support a safe evacuation process. The combination of both hard and soft measures is very important for reducing the loss caused by a major tsunami. This tsunami has taught us that natural disasters can occur repeatedly and that their scale is sometimes larger than expected.
1. Introduction
On 11 March 2011, a strong earthquake of
magnitude M = 9.0 (JMA, 2011) occurred in East Japan,
generating a devastating tsunami. No one was
expecting an earthquake of this magnitude in Japan.
Japan is well known as a leading tsunami disaster
prevention country, because it has countermeasures
and evacuation plans set in place. Along the Sanriku
ria coast, where V-shape coastlines can cause a
tsunami wave to accumulate inside the bay, tsunamis can
easily be amplified to heights exceeding 10 m.
Therefore, many structural and non-structural tsunami
countermeasures were constructed along the Sanriku
coast (ABE and IMAMURA, 2010). Nevertheless, the
600 km Sanriku coast, which extends northwards
from Sendai and covers the Miyagi, Iwate, and
Aomori prefectures, was heavily damaged by the 2011
tsunami. Some of the damage was observed during
primary damage field surveys in Miyagi (SUPPASRI
et al., 2012a) and Iwate prefectures (YALCINER et al.,
2012). In this paper, the effectiveness of these
countermeasures during the 2011 tsunami, and the
mechanisms by which they were damaged, are
discussed briefly; examples of breakwaters in Kamaishi
and Ofunato; tsunami gates in Fudai and
MinamiSanriku; seawalls in Taro, Yamada, and Ishinomaki;
and control forests in Rikuzentakata and Natori are
discussed. The damage to houses in relation to the
materials that were used and number of stories is also
discussed; overturned reinforced concrete buildings in
Onagawa are presented as examples. Similar to the
lessons learned from the 2004 Indian Ocean tsunami
(SANTOS et al., 2007; SUPPASRI et al., 2012c), the
lessons learned from this tsunami, including those
regarding the effects of the tsunami on a highland
residence in Toni-Hongo, the Namiwake shrine in
Sendai, and damage data from historical tsunamis in
the Sanriku area, are discussed. Examples of
successful evacuations, for example the Miracles of
Kamaishi and Inamura no Hi, the tsunami festival
in the Wakayama province are provided.
2. Historical Tsunamis that have Affected
the Sanriku Coast and Sendai Plain Areas
The Sanriku coast is often hit by giant tsunamis. If
we limit our discussion to tsunamis generated by
earthquakes over M8.0, the first historical tsunami is
the Jogan tsunami in 869, followed by the
KeichoSanriku tsunami in 1611, the Meiji-Sanriku tsunami
in 1896, the Showa-Sanriku tsunami in 1933, the
farfield tsunami from Chile in 1960, and the Great East
Japan tsunami in 2011 (Fig. 1; Table 1). The 1896
tsunami caused nearly 22,000 deaths (YAMASHITA,
2008a), the highest number of deaths caused by a
tsunami in Japanese history. In fact, large earthquakes
such as that which generated the Jogan-type tsunami
occurs, on average, every 8001,100 years (MINOURA
et al., 2001). More than 1,100 years have passed
since the Jogan tsunami, so there was a high
probability that a large earthquake and tsunami would
occur. However, with only one historical record of
the Jogan tsunami and the limited Jogan tsunami
depos (...truncated)