Incident Wave Crest 

 (time 0). 



Figure 36. 1960 tsunami refraction, Hilo, 



Hawaii (after Palmer, Mulvihill, 

 and Funasaki, 1965). 



Applying Snell's Law where the wave moves through some incremental 

 distance, with an incremental change in water depth d, and assuming 

 that there is a shallow-water wave so that the celerity C is given by 



C = (gd) 1/2 

 then the incremental refraction of a wave ray is defined by 



(225) 



sin(ct + da) _ / d + dd \ 

 sin a \ d / 



1/2 



(226) 



or, squaring both sides of equation (226) , 



sin 2 (a + da) _ (d + dd) 

 sin 2 a d 



(227) 



109 



