Tsunamis are translational long waves created by the seafloor displacement. Here we focus on tsunamis triggered by co-seismic fault rupture. Geophysical time-and-space scales relevant to tsunami phenomenon are discussed, emphasizing its unique natural hazard phenomenon. Characteristics of tsunami generation, propagation, and inundation are also presented.
Then, lessons learned from the 2011 Heisei Tsunami are presented. This 2011 event has altered our traditional concepts on tsunami hazards. Prior to this event, it was understood that reinforced concrete structures could withstand tsunami actions. This concept is no longer the case. Many concrete buildings and coastal protective structures (seawalls and coastal dykes) failed by rotation. Several failure patterns of seawalls and coastal dykes are examined. Flow-induced suction pressures on the crown must play a role in the failure of concrete panels that had covered dyke’s infill. High-speed flows together with high compressing pressures caused the formation of scour at the leeside foot of the dyke. Then, we examine a couple of reinforced concrete buildings that were exposed to similar tsunami loadings, but one was toppled and the other survived. The presence of soil foundation causes a time delay and attenuation of the buoyancy effect on the buildings. The buildings are also stabilized by the weight of water that has flooded the inside. A few directions are discussed for the development of design considerations for buildings and coastal structures to cope with the “beyond-the-design-basis” extreme coastal hazards. At the conclusion, some conceptual strategies to approach such complex problems of extreme natural hazards are presented
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Harry Yeh is a Professor in Civil Engineering at Oregon State University. He received an AB in Economics from Keio Gijuku University (Japan), BS and MS degrees in Agricultural Engineering from Washington State University, and a PhD in Civil Engineering from University of California. He worked for Bechtel Inc. in the late 1970s and early 1980s, primarily analyzing hydrodynamics problems involved in electric power plants. Professor Yeh began his academic career in 1983 at the University of Washington, then joined the faculty of School of Civil and Construction Engineering at Oregon State University in 2003. His primary research interest is in the field of hydrodynamics of tsunamis, focusing on controlled laboratory experiments and theoretical development of nonlinear long-wave theory. Professor Yeh participated in several reconnaissance field surveys for tsunamis – from the 1992 Nicaraguan event to most recent Japanese Tsunami in 2011.
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