SOLUTION: 



, . , 30+60+90+120+150 nn .. . 



(a) h = = 90 centimeters 



avg 5 



(h ) 2 = 8,100 square centimeters [8.72 square feet) 



(b) (h 2 ) 



*■ avg 



30 2 + 60 2 + 90 2 + 120 2 + 150 2 



(h 2 ) = — = 9,900 square centimeters (10.66 square feet) 



(c) From equation (16), 



(h 2 ) 

 E- pgA 2H£ 



2 



E = (1.0252)(980.7)(5)(2.3 x 10 12 ) 9,90 ° 



2 



E = 5.72 x io 19 gram-square centimeters per second squared 

 = 5.72 x 10 19 ergs (4.22 x 10 12 foot-pounds) 



************************************* 



The horizontal motion along a rupture line may contribute very little 

 to tsunami generation. The maximum energy input from the horizontal 

 motion would occur when the rupture line is normal to the continental 

 slope. The motion along the rupture line, in that instance, would be 

 equivalent to a wedge moving a short distance through the water (see Fig. 

 7). Berg, et al . (1970) show that for a motion equivalent in magnitude 

 to that of the 1964 Alaskan earthquake, and acting normal to the continen- 

 tal slope, the potential energy input to the resulting tsunami would have 

 been 3.12 x io 2u ergs (2.3 x io 13 foot-pounds). This is less than 1.5 

 percent of the energy input from the vertical uplifting, and seems to 

 confirm Iida's (1970) analysis which showed that major tsunamis are asso- 

 ciated with the dip-slip fault type. In fact, the rupture line of the 

 1964 Alaskan earthquake was almost parallel to the continental slope, and 

 the energy input from the horizontal motion would have been negligible in 

 this case. In other cases, the contribution of horizontal motion may be 

 greater. 



2. Initial Wave Formation . 



Because of their long periods and corresponding long wavelengths, 

 the train of waves forming a tsunami is taken to be shallow-water waves 

 at their origin, and propagates across the ocean as shallow-water waves. 

 The actual form of the wave train is determined by the initial generating 

 mechanism, i.e., the area of the uplifted sea bottom, the height of and 



34 



