Section IX. SUMMARIZED CONCLUSIONS 



It seems desirable to set out in succinct form the broad conclusions 

 and immediately useful information which appear to emerge from this study. 

 For convenience these are listed by categories. 



1. Earthquake and Tsunami Generation Characteristics 



a. The tectonic earth movement of the Alaskan earthquake giving 

 rise to the main tsunami, was a dipole (crest-trough) ver- 

 tical deformation over the Continental Shelf of the Gulf of 

 Alaska, accompanied by a differential horizontal thrust of 

 the land seaward. 



b. The earth deformation apparently occurred as result of a 

 differential dislocation along a low-angle fault-plane 

 and possibly also, a near-vertical buried fault-plane, 

 extending over a distance of 800 kilometers. 



c. This fault length confirms an empirical-statistical result 

 (Equation (2), p. 28), based on world data, which permits 

 approximate prediction of fault length from earthquake 

 magnitude . 



d. The frequency of occurrence of earthquakes in Alaska, as 

 a function of magnitude, follows the trend of world data 

 and of independent Japanese data. The probability of 

 occurrence of an earthquake of the magnitude (8.5) of the 

 Alaskan earthquake in the Alaska-Aleutian Island region 

 is about 1 in 30 years. 



e. The maximum resultant earth deformation confirms an em- 

 pirical statistical trend of world data (Figure IT) which 

 permits approximate prediction of expected maximum tectonic 

 deformation in terms of earthquake magnitude. 



f . Defined by backward refraction of the waves from recording 

 stations around the Pacific Ocean, the tsunami source region 

 occupies the Continental Shelf of the Gulf of Alaska, out 

 to the Aleutian Trench over a distance of 800 kilometers . 



g. The equivalent diameter of this source region (S = i+25 

 kilometers) confirms an empirical-statistical result 

 (Equation (3), p. 38) based on Japanese data, which permits 

 approximate prediction of tsunami source size in terms of 

 earthquake magnitude. 



h. The initial deformation of the sea surface over the Conti- 

 nental Shelf during the earthquake was probably a smoothed 

 replica of the vertical earth deformation, and comprised a 

 dipole wave with a probable crest height varying perhaps 

 from 30 to 60 feet. 



373 



