178* <70* 168' 160' IBS* 150° 145° 140' 185' 130' 128* >20' 



!„,_ i 1 1 1 r 



jrage"?, 



ALASKA 



Figure 13. Surface elevation contours 13,000 seconds after the 1964 

 Alaska earthquake (from Hwang and Divoky, 1975) . 



The use of equation (125) at the open boundaries results in an error 

 in the computed wave heights at those boundaries. As computations are 

 carried out for the entire computational grid at each time step, the 

 error propagates through the grid at successive time steps. This error 

 will have the appearance of a wave reflected from the open boundary. 

 Shaw (1974, 1975; Shaw, Department of Engineering Science, State Univer- 

 sity of New York, Buffalo, personal communication, 1977) suggests that 

 an outer boundary integral equation method can be used to eliminate the 

 error at the open boundaries . The outer boundary integral equation would 

 be used to determine the wave height, n, and its normal derivatives at 

 the boundary; those values would be used in the finite-difference solu- 

 tions for the interior region. 



6. Nearshore Computer Models . 



For waves in the nearshore region, Peregrine (1967) developed finite- 

 difference equations for the two-dimensional case of a wave shoaling on 

 a beach. Defining 



u, = u(rAx, sAt) (r = l,...,n s = l,...,n) 



I ,b 



n = n(rAx, sAt) 



60 



