240 Long Waves in Canals and Standing Waves in Closed Basins 



4 5 



Hours (April 2 ) , G.C.T. 



Fig. 101. Tide gauge record at Valparaiso following the earthquake of 1 April 1946. 



station, however, the period decreases slowly with time, e.g. in Valparaiso 

 from 17 to 7-5min. The increase of the wave period with increasing distance 

 from the origin appears to be a general phenomenon. Munk (1947, p. 198) 

 has solved the problem from a theoretical viewpoint. 



If a wave with a wave length A and a period T travels with a wave 

 velocity c along the +.r-axis, its wave length X changes according to the 

 relation 



dk _8X 8X 



dt ~dt^ C dx % 



(VI. 148) 



This change can also be found from the rate at which the wave "stretches' 

 due to the difference in velocity of two adjoining crests. This gives 



dX __ .dc 

 di~ dx 



If we add the identity I = cT, 



dt dx 



(VI. 149) 



(VI. 150) 



