An interesting survey :
Apart from the magnitude of the earthquake and resultant tsunami, one of the key reasons for devastation is Japan's land character. Almost 70 percent of the country's land is covered by mountains, which leaves a very narrow coastal belt. The devastation of tsunami was found to be the largest in two types of land areas. The first is areas with a narrow opening to the sea, like that of Taro in Miyako town. The other is areas of vast, flat lands, like Rikuzentakata (in Iwate prefecture) or Watari, Yamamoto-cho (in Miyagi prefecture).
Taro is famous for its tsunami prevention measures. The town was affected by the 1896 tsunami (known as the Meiji Sanriku earthquake and tsunami), which killed more than 22,000 people. The town lost most of its population in that disaster. In 1933, the town was again hit by another devastating tsunami, following a decision by the town leader to construct a mega dyke to protect its people. The dyke was built in several phases, becoming a 10 meter-by-2.5 kilometer long structure. The latest tsunami wave overflowed this dyke and damaged some areas, but would have been more devastating without the dyke. The importance of infrastructure-based disaster prevention can be highlighted here.
In Kamaishi, Iwate prefecture, an eight-story tsunami evacuation building stood undamaged very close to the shoreline. On the hazard map, distributed by the city government, this building was designated and marked as an evacuation building with clear instruction that people need to evacuate higher than the fourth floor. What is more interesting is that, on March 3 (also the day of the 1933 Showa Sanriku earthquake and tsunami) an evacuation drill was performed with local residents and school children. Therefore, tsunami awareness was rather fresh in their minds and people took shelter in evacuation buildings and on a nearby evacuation road (a pre-designated road on the nearby mountain with access stairs), immediately when they felt the earthquake. This shows the importance of evacuation drills and disaster education.
In contrast, in Rikuzentakata, where there was rather vast land in the coastal area, the tsunami wave entered as far as 4 km inland, caused extensive damage to the local government building, and made it non-operational in the immediate rescue relief phase. A distinct difference in the post-disaster operation can be observed in the cities where the local government office was not affected due to its location on higher ground. In Ofunato in Iwate Prefecture, or in Iwanuma, Yamamoto-cho, in Miyagi Prefecture, the local governments already started their preparations for the short- and medium-term recovery phase, including construction of temporary shelter. In contrast, in Minamisanriku, where the three-story disaster management office was also destroyed, the relief phase has been prolonged.
For early warning systems to be effective, a proper risk communication mechanism, which links both information provider and receiver, is needed. In the March 11 disaster, the tsunami warning and tsunami advisory were issued within three minutes after the event.
The warning was broadcast though the Japan Meteorological Agency webpage, television, radio, social networking media, and also through announcements from the town and city offices. However, in several places, initially, people underestimated the height and severity of tsunami, and started evacuating after the first wave had arrived. What makes people take immediate action for evacuation? An easy-to-understand early warning (with information on potential tsunami height), evacuation orders and repeated evacuation drills make a difference. In some cases, people had a ''feel safe'' misperception, where neighbors' and children's roles became important.
What is an ideal tsunami prevention measure? There is possibly not a single formula applicable to every place. It needs to be customized based on local geographic and topographic conditions. A combination of early warning systems, infrastructure measures like coastal dykes, tsunami evacuation centers, and awareness and education campaigns including evacuation drills and disaster education is required.
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