TSUNAMI ENGINEERING 



by 

 Frederick E. Cornfield 



I . INTRODUCTION 



The term tsunami is derived from two Japanese words: "tsu," meaning 

 harbor, and "nami," meaning wave. Tsunamis, or seismic sea waves, have 

 very long periods and are not easily dissipated. The waves may create 

 large surges or oscillations in bays or harbors which are not responsive 

 to the action of normal sea waves. In the original definition, the term 

 tsunami was applied to all large waves, including storm surges. However, 

 recent definitions have limited its application to waves generated by 

 tectonic or volcanic activity. Western literature previously referred 

 to these waves as tidal waves or seismic sea waves, but those terms have 

 generally been replaced by the term tsunami. 



Tsunamis are primarily created by disturbances in the crust of the 

 Earth underlying bodies of water, and the resulting uplifting of the 

 water surface over a large area which forms a train of very long-period 

 waves. The waves may have periods exceeding 1 hour, in contrast to nor- 

 mally occurring wind-generated sea waves which have periods less than 1 

 minute. When tsunamis are generated by volcanic activity or landslides, 

 the wave energy tends to spread along the wave crests and the tsunamis 

 affect mainly the areas near their source. Tsunami waves generated by 

 tectonic uplifting may travel across an ocean basin, causing great 

 destruction at locations far from their source. 



Because of the potential destructive effects of tsunamis, it is 

 necessary to understand the mechanisms of their generation and propaga- 

 tion, and to be able to predict the extent of flooding and the effect of 

 wave forces in coastal areas subject to tsunami attack. Proper control * 

 must be exercised over the use of such areas, and in designing structures 

 to be placed in these areas. Also, sufficient warning of a tsunami 

 attack must be given to people located in these areas, and procedures 

 must be established for an orderly evacuation when necessary. 



This report discusses the prediction of tsunami effects in coastal 

 areas and attempts to provide guidance in determining the flooding 

 and wave forces at any particular location. The present knowledge of 

 tsunamis and the deficiencies in this knowledge are summarized. 



1. Nature and Origin of Tsunamis . 



Areas of seismic activity which could potentially generate tsunamis 

 are shown in Figure 1. The major part of this activity occurs along the 

 boundaries of the Pacific Ocean, with other regions of strong activity 

 primarily concentrated in the Caribbean and Mediterranean areas. Van Dorn 

 (1965) indicates that the Japan Trench radiates detectable tsunamis at the 

 rate of about one per year. Lesser amounts of activity occur elsewhere. 



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