e. It follows from (d) that certain coastal areas vill always 

 "be peculiarly susceptible to large damaging waves from 

 great tsunamis whose energy content is high in keeping with 

 large earthquake magnitudes; (Port Alberni, Canada; Crescent 

 City, San Francisco, and Santa Monica, California; Hilo and 

 Kahului, Hawaii; and Lyttelton, New Zealand, are cases in 

 point ) . 



f. Generally, tsunami wave height decays with distance from 

 the source; in one-dimensional propagation, as the inverse 

 1/3 or 1/2 power of the distance, and in two-dimensional 

 (radial) propagation as the inverse 2/3 or 5/6 power of 

 distance, respectively, near the front of the waves and 



in the body of the waves. 



g. There would appear to be a natural tendency for dynamic 

 amplification of the height of tsunami waves reaching a 

 straight coastline over a uniformly sloping Continental 

 Shelf. This is indicated by theory, but is as yet 

 unconfirmed by experiment. 



h. Some evidence exists to show that the Alaskan earthquake 

 produced waves of from 3 to 5 hours period, possibly 

 resulting from the seaward thrust of the coastal landmass, 

 or developing as nonlinear subharmonic responses to the 

 ocean boundaries. 



3. Features of Tsunami Damage 



a. Tsunami waves from the Alaskan earthquake had their most 

 damaging effects when they occurred on the high spring 

 tide. 



b. The possibility of relationship of earthquakes of large 

 magnitude with times of high spring tides predicates a 

 design criterion that concurrence of high spring tide with 

 maximum tsunami wave height should always be considered. 



c. At Seward, Valdez and Whittier, heavy tsunami damage was 

 caused by submarine slide-generated waves of about 3 to 

 5 minutes period and 30- to l40-foot height. These waves 

 broke with bore effect on the coastlines and displaced or 

 smashed objects in their path. 



d. At Kodiak, Alberni, and Crescent City, as also at Seward 

 and Valdez, the main tsunami waves, with or without over- 

 riding harmonics or local seiche waves, acted as fast- 

 rising and ebbing tides, without bore formation (except in 

 the narrow Wear Island channel at Kodiak). They buoyed 

 objects and moved them with massive and sustained stream 

 effect against nonmoving objects. 



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