Van Corn's interpretation of the tsunami -generation mechanism is 

 additionally based on the initial wave types arriving at recording 

 stations around the Gulf of Alaska and on a long-practiced Japanese 

 technique of establishing the tsunami source by refracting waves back- 

 ward from the stations out to deeper water over travel times equivalent 

 to the intervals between the time of occurrence of the earthquake and 

 the arrivals of first waves at each station (Figure 25a). In Figure 25b 

 Van Dorn has reconstructed possible initial wave fronts which accord with 

 the previous figure. He hypothesizes that the extent of surface uplift of 

 the seabed reached as far as the Aleutian Trench with a ridge of maximum 

 uplift along an arc extension of the uplift crest through Montague Island, 

 roughly parallel to the hinge line of zero ground elevation. This concept 

 is generally supported by Plafker and Mayo (1965), whose picturization 

 is shown in Figure 26a. Pararas-Carayannis (1965), in a wave refraction 

 study somewhat similar to Van Dorn's, arrives at the tsunami source region 

 shown in Figure 26b. 



Figures 25 and 26 agree in the main, although Pararas-Carayannis' 

 initial wave front is a considerable distance landward of the Aleutian 

 Trench axis and thus differs from Van Dorn's interpretation. A possible 

 weakness of both investigations lies in attempting to define the major 

 wave front on the open sea side from such oblique station data. Also, it 

 seems that no consideration has been given to the fact (largely because 

 it was not then known to the authors) that the entire Continental Shelf 

 suffered a horizontal thrust in a south and south- southwest direction 

 (Figures 15 and I6). 



The initial velocity communicated to the water from this thrust 

 woiild help to throw a great deal more energy toward the southwest than 

 might otherwise be the case. It would also promote more rapid elevation 

 of the tsunami crest seaward of the ridge of maximum crustal uplift. It 

 would not otherwise affect the speed of tsunami propagation. 



We have considered it important and desirable to examine the propa- 

 gation of the tsunami across the entire Pacific Ocean and have therefore 

 prepared a plot of the continuous wave fronts at one-hour intervals from 

 their source to their destinations at tide gage stations throughout the 

 Pacific arena (Figure 27). In developing this chart on Mercator projec- 

 tion, the wave fronts have been drawn to be consistent with the arrival 

 times tabulated by Spaeth and Berkman (1968) (see Table B-1, Appendix B) 

 and the travel rates in different depth d of water at the velocity of 

 long waves c = /gd, g being the acceleration due to gravity. The dis- 

 torted scale of Mercator projection causes the map distance-intervals be- 

 tween wave fronts to appear larger at high latitudes than at low latitudes. 

 Nevertheless, a consistent picture is established which accomodates all 

 the observational data and the varying velocity of travel with depth. In a 

 few cases station arrival times in parentheses have been used in preference 

 to those (unbracketed) given by Spaeth and Berkman. These adjustments are 

 based on careful examination of the tide gage records and will be reported 

 in the next section. 



Text resijmes on page 39 



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