APPENDIX D 



THE FLOW AND FORCE FIELD OF TSUNAMI WAVES 



By Basil W. Wilson 



Recognizing that tsunami waves are of very great length and period 

 .n shallow water and also of considerable aiTiplitude, in relation to the 

 iepth, by the time they reach the coast, we are led to enquire into tlie 

 lature of the water velocities and the forces which these waves can bring 

 ;o bear against obstacles of any kind. 



Most records of tsunami waves (as, for example, Figs. 43 to 66) 

 show that they have little resemblance to cnoidal or solitary waves, but 

 3n the contrary are strongly sinusoidal, as also are the much longer period 

 istronomical tidal waves. The existence of what are effectively Airy waves 

 .n such shallow water (very small values of H/T^ and d/T^) poses a 

 Droblem which the writer has not at present resolved; since the dictates of 

 shallow-water wave theories seem to prescribe otherwise. 



The periods of waves found to occur as a result of the Alaskan earth- 

 quake cover the range from about Z mins. to 5 hours. The relative capacity 

 Df these waves to produce damage is a matter of prime interest. Because 

 Df the above mentioned observation of the apparent sinusoidal character of 

 the waves, we resort to the finite -amplitude wave theory of Lamb (1932 Edn. , 

 pp. 278-280) which uses the Method of Characteristics to show that a long 

 wave of elevation tj above water level of depth d propagates at the velocity 



/"gd" '_ 3(1 + -nld)^'^ -2 ] (D-1) 



D-1 



