h. Height Characteristics of the Main Tsunami 



Table III lists maximum envelope heights Hi and average periods 

 T]_ of the first three waves in the leading beat of the primary wave 

 systems. It also gives heights and periods of secondary wave systems. 

 Travel times t are based on arrival times of the waves from Figures k3 

 through 66, In many cases these differ somewhat from the arrival times 

 of Spaeth and Berkman (1968), see Figure 27. For the first six stations 

 in the table the distance r is the length of the refracted wave ray 

 connecting the source and the station as evolved in Figure 27. For 

 all other stations, the distance r is the great circle distance of 

 wave travel given by Spaeth and Berkman. 



Equation {k) is invoked to calculate the mean depth along the total 

 distance to each station from the relationship 



d = (r/t)2 /g (12) 



Relative distance is then the ratio r/d. 



An assumed wave height H^ at the source has been adopted according 

 to the arguments presented in Figures 3^, 36, and 37. Because of the 

 finding of von Huene, et al (1967), that a very high center of strain 

 release existed near the southwest end of the inferred tsunami source 

 region, we have adopted Hq = 60 feet for all stations beyond the first 

 six. Figure 27 suggests that nearby stations received most of the wave 

 energy spread laterally from the source length, whereas the distant 

 stations received wave energy predominantly from the radial expansion 

 of the southwest end disturbance. These wave heights at the sources, 

 although speculative, provide a comparative basis for investigating 

 some properties of wave decay. 



The inference seems clear that the tsunami that traversed the 

 Pacific Ocean comprised packets of extremely long waves with periods of 

 about 1.8 hours. At insular and continental shelves, some of the energy 

 of the waves was reflected and scattered and some transferred to high 

 frequencies so that the residual energy remaining to the fundamental 

 waves, as represented in the height Hj, has in many cases been much 

 depleted. Nevertheless, even the height Hj is nominally greater than 

 the height H the long waves would have at the shelf-edge, because of 

 the height enhancement from shoaling. Rating this enhancement as 50% 

 on average, the deepwater height ratio H/Hq is taken as 2/3 (Hi/Hq). 



Values of H/Hq have been plotted against relative distance r/d in 

 Figure 70. The range of values of r/d from all these data is limited 

 so that it is difficult to establish trends. However, if we assume that 

 for a value of r/d = 1, the ratio of H/Hq would have to be unity, we may 

 perhaps draw some conclusions. We are assuming that r/d = 1 effectively 

 represents the fringe of the initial wave at the source, at or near the 

 continental slope of the Aleutian Trench. 



98 



