1B. Research on Tsunami Disaster Prevention and Mitigation

Background and Objectives

  • Japan has suffered repeated damage by tsunamis, and further massive tsunamis are expected to be caused by mega-thrust earthquakes such as the Tokai, Tonankai, and Nankai earthquakes. Therefore, PARI and other institutions have conducted research on the prevention and mitigation of tsunami disasters. Research in this field has made great progress since the 2004 Indian Ocean Tsunami, and disaster-prevention measures have been implemented in various regions. However, the 2011 Great East Japan Earthquake and tsunami caused unprecedented damage. When considering the possibility of giant tsunamis in the future such as those in 2011, further research and development are needed to save people’s lives, reduce economic losses, and facilitate early restoration and reconstruction.
  • This research theme therefore involves engineering-oriented research and development on tsunami propagation and inundation, stability of structures against tsunamis, combined earthquake/tsunami disasters, etc.

Research topics

 Concerning this research theme, we are conducting the following research, which is focused on tsunami disaster mitigation and early recovery.

  1. Research on earthquake-tsunami compound disaster
     Regarding combined earthquake/tsunami disasters caused by a large mega-thrust earthquake, we are investigating disaster mechanisms on the basis of laboratory experiments and developing numerical models for disaster prediction. The experimental studies involve developing facilities that combine a geotechnical centrifuge and a tsunami flume.
  2. Research on structural and nonstructural tsunami countermeasures
     We are developing countermeasures to control the damage to structures caused by tsunamis exceeding the design parameters, performance verification methods to predict the displacement of structures, and hardware technologies to reduce tsunami energy.
  3. Research on tsunami disaster scenarios
     In addition to a real-time tsunami hazard mapping technology, we are developing an evacuation simulator to assist early evacuation. We are also exploring ship motions induced by tsunamis, and considering safer procedures for ship evacuation. Moreover, we are reviewing techniques for creating scenarios including early recovery of orts, and promoting the practical use of such scenarios.

Activities in FY 2014

  • We proposed a method for examining the overflow over overing blocks behind widened levees. We also proposed  formula for predicting overflow scouring and a formula or calculating the tsunami force that affects breast walls, pright tide embankments, and the like. These results ere reflected in the "Guideline for Tsunami-Resistant esign of Breakwaters" and utilized for measures against sunamis by means of breakwaters and tide embankments. he results are also planned to be reflected in the Technical Standards for Port and Harbour Facilities," hich are now under revision.


Photograph 1.1.1.1 Scenes of experiments on overflow over covering locks behind widened levees

  • We investigated the damage to 23 ships moored in Kashima ort at the time of the Great East Japan Earthquake and identified the relation between drifting ships and the damage to port facilities. We also clarified that 100,000 ton-class large ships had an impact speed of 2 m/s even nine hours after the earthquake; the breakdown of drift types was Parallel: 37%, Oblique: 21%, and Rotated: 21%, the breakdown of collision portions was Bow/Stern: 54% and Side: 29%, and there is less possibility of collision because of slow flow at the shallow inner part of the port.
    These research results are expected to help improve the safety of ships against tsunamis.

 

Figure 1.1.1.3 Wakes and points of collision of drifting ships and the maximum flow velocity

 

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