Tuesday, 11 November 2014


If you're on a coast adjacent to a subduction zone and you experience prolonged or intense shaking, the sensible thing to do is to evacuate in case the earthquake is followed by a tsunami. High ground provides the safest place to evacuate to, but if you're on a wide, flat coastal plain, you may not have time to reach the closest slope. Particularly in areas close to the fault, where you may only have a few minutes before the first wave hits (perhaps 5-15 minutes in the case of some of the south central Japanese coast), high ground will take too long for many people to reach. 

One solution is vertical evacuation. Particularly following the Tohoku earthquake in 2011, tsunami evacuation towers have been built in vulnerable locations along the Enshunada coast. The concept is simple - build a tall tower capable of withstanding both intense shaking and the tsunami wave and evacuate vertically in the event of an earthquake. The photos here are from the Otagawa lowlands, approximately 30km east of Lake Hamana.

Tsunami evacuation tower seen from the ground level. The top is at approximately 15m above sea level.
The view to the west from the top of the evacuation tower. The coastal plain stretches for more than 30km in this direction. QRN team members in the foreground.
The main space for evacuation. The top floor can hold 180 people and the entire structure can hold 400. Solar panels provide an electrical supply.
Yokoyama-san investigates the contents of an emergency supply box on the top of the evacuation tower.

Building retrofitted with external steps for tsunami evacuation
The concept of vertical evacuation up artificial mounds in response to extreme waves is not new. Here QuakeRecNankai team member stand in front of an artificial mound built in 1680 for evacuation during typhoons. It was last used 30 years ago.
The life-saving hill at Minato
Artificial mounds continue to be created alongside evacuation towers.
While tsunami evacuation towers and mounds are clearly essential for saving lives in vulnerable regions with flat coastal topography, in densely populated areas, the capacity of vertical evacuation structures may be insufficient and other solutions must also be found. 

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