REPORT ON OCEANOGRAPHY 65 



detail of water movement accompanying the passage of storm across 

 these basins (FE, 6, 1950, 22-33). 



Tsunamis 



The coastal areas of Japan have frequently been attacked by the 

 storm waves (surges, or Takashio) caused by typhoon and also by tsu- 

 namis caused by submarine earthquakes. To protect the coastal areas 

 from damages due to such high waters, a number of studies has been 

 made on these problems. 



A series of theoretical research was published in the years preced- 

 ing 1950 by R. Takahashi. In 1951, he published a very intensive work 

 on the amount of energy of tsunami waves arriving per unit length 

 of segment along the Pacific coasts of the Japanese islands per century. 

 This research is very useful to anticipate the possible damages by tsu- 

 nami attacking our islands in future, providing the seismic activities 

 remain unaltered for the time being (ERIB, 29, 1951, 76-96). 



T. Ichiye has published another series of papers on tsunami. In 

 1949, he made a model experiment of the tsunami waves entering Osaka 

 Bay from the Pacific Ocean and studied the patterns and characteristics 

 of the oscillations peculiar to several portions of this bay around which 

 are located many important industrial and commercial cities in the 

 heart of Japan. He also attempted to take the effect of viscosity into 

 consideration (KS, 26, 1949). 



Afterward he propounded a theory of tsunami and discussed the re- 

 flection and penetration of tsunami waves as they pass into the shelf 

 taking into account the interrelation between the length and period 

 of tsunami waves and the depth and bottom slope of the shelf, and ob- 

 tained a correction to Green's law of change in amplitude. He also suc- 

 ceeded in computing the reflectivity and permeability of tsunami which 

 attacked Osaka Bay just mentioned from several directions of the Pa- 

 cific. He also took into account the effect of viscosity on the shelf 

 (KS, 27, 1949; OM, 2, 1950). He also established a theory of tsunami 

 caused by a travelling disturbance on the bottom. This theory of tsu- 

 nami produced by a moving source is very helpful in treating the ob- 

 served waves of tsunami. He first computed the tsunami waves when 

 the submarine dislocation moves in a direction and showed that there 

 occurs in a train of waves if the velocity of source is smaller than that 

 of long waves, and a solitary wave is produced when the source moves 

 faster than the long wave (KMOM, 8, 1950). Next, he treated the 

 case where a circular elevation or depression is moving on the bottom. 

 The patterns of oscillations remain the same except that the wave 

 height decreases as the reciprocal of the square of the distance (KMOM, 

 9, 1951). 



