magnitude of the tsunami signature in Figure i+9c. The degree of accuracy 

 of Figure 27 limits an explanation of this kind to little more than sug- 

 gestion, but one aspect that is possibly substantiative concerns what 

 happened on either side of Crescent City. Thus at Victoria, Canada 

 (Figure it8d) and at San Francisco, California (Figure 50c), the leading 

 modulation has been shortened by an interference effect, yielding a 

 short intermediate beat not found in the tsunami signatures north of 

 Victoria, nor even in the signatures south of Rincon Island, California 

 (compare Figures 51c and 53c). 



Causes for the high waves at Crescent City have been sought by others, 

 notably Foley ( 196^1 ), Tudor (196U), Roberts and Chien (1965), Wiegel (1965), 

 Kent (1965) and Raudio (1965), but with no positive conclusions. Roberts 

 and Chien impute the concentration of wave energy on Crescent City to the 

 refractive effect of a distant sea mount in deep water. We are not con- 

 vinced of this argument because of the small size of these topographical 

 features, relative to the great length and period of the tsunami. Never- 

 theless, the caustic formations envisioned by Roberts and Chien would at 

 least enhance any larger caustic accumulation of energy coming from the 

 source. 



The possibility that continental-shelf resonance amplified the wave 

 effect at Crescent City will be discussed later. However, Crescent City 

 has been peculiarly subject to high wave effects from numerous great 

 tsunamis (Magoon, 1962; Wiegel, I965; Raudio, I965), though this tsunami 

 was the greatest of them all. 



The wave rays of Figure 27 indicate that the energy distributed 

 along the South American coastline originated from a very small sector 

 of the southwest extremity of the source region. Nevertheless, Figure 

 53c for Talcahuano, Chile, shows waves k feet high of 1.75 hours period 

 in a fish-shaped beat; the largest amplitude is carried by the second 

 trough, and 8 waves occur in the beat. At Corral, Chile, about I80 

 nautical miles south, the primary waves were 2 feet high and about 

 1.9 hours in period; 9 waves are found in a similar fish-shaped beat 

 (Figure 5^c). 



The effect of the East Pacific Rise on the tsunami is apparent in 

 Figure 27 by the refraction of the wave fronts and the focusing of wave 

 energy toward the southern tip of South America. At Ushuaia, Tierra del 

 Fuego, Argentina, the tsunami signature is still characteristically a 

 beat of long waves 1 foot high with a period of about 1.9 hours (Figure 

 55c), but the highest waves are now further removed from the front. 



The natxoral refractive process allows little wave energy leakage 

 through the Drake Passage, which forms a window to the South Atlantic 

 Ocean (Figixre 27), while considerable spreading of energy also occurs 

 along most of the Antarctic continental boundary to the Pacific Ocean. 

 Despite this, enough energy reached Palmer Peninsula in Antarctica to 

 register the tsimami signature and a variety of superimposed oscillations 

 (Figure 56c) . 



94 



