Plafker (1965), on the basis of field observation and qualitative 

 arguments, proposed a low-angle plane with predominantly thrust motion 

 as accountable for the earthquake deformation (see Figure lU). These 

 apparently conflicting results have been discussed further by Savage and 

 Hastie (1966) and by Stauder and Bollinger (1966). The first pair of 

 authors apply the theory of Maruyama (196U) to determine the surface 

 deformation for a dislocation model of thrust faulting. The results of 

 their calculations for three such models are shown in Figure 19b. Model 

 1 tends to be comparable with that obtained by Press and Jackson (1965). 

 Model 3, however, yields results much more akin to the actual surface 

 deformation shown in Figure ik. Savage and Hastie therefore tend to the 

 view that thrust faulting was the more likely cause of the earthquake. 



Stauder and Bollinger proceed to show that fault-plane solutions 

 based on the main shock of the earthquake and numerous subsequent shocks 

 are consistent with both interpretations of thrust faulting and dip-slip 

 faulting. Their equal-area projection of the focal mechanism solution 

 based on seismic P-wave data is shown in Figure 20, and indicates a fault 

 plane with a strike N 66° E and a dip 85° SE, in close agreement with 

 Berg (196U) and Algermissen (1966). Their fault plane solutions based on 

 various aftershocks in the Prince William Sound. and Kodiak Island regions 

 are shown in Figure 21 a and b. Besides the dominant, almost vertical 

 plane lying along the axis of the epicenter belt, these authors found 

 the second plane to have a strike bearing mainly to the northeast and a 

 dip between about 5° to 15° northwest. Such a plane would be consistent 

 with that envisioned by Plafker (1965), Figure 1^. 



Stauder and Bollinger then advanced the work of Savage and Hastie by 

 applying the Maruyama theory to the second (thrust) fault plane on the 

 supposition that a differential slip occurs along it, as shown in Figure 

 22b. Their computed vertical and horizontal deformations of the earth's 

 siorface are in remarkably good accord with some of the latest measured 

 data provided by Plafker (Figure 22a). A refinement of their calculation, 

 allowing for some vertical thrusting at the locations corresponding to 

 the Hanning Bay and Patton Bay faults on Montague Island even simulates 

 the discontinuities of profile found there (Figure 22c). Stauder and 

 Bollinger favor the thrust plane mechanism for the earthquake, so ably 

 argued by Plafker (1965). The present writers concur with this view in 

 the main, particularly insofar as the thrust plane mechanism also offers 

 an explanation for the horizontal displacements already noted in Figure 16. 



However, the tendency of the flow lines of thrust to bear south and 

 southwest (Figure 16) suggests that a degree of strike-slip and dip-slip 

 may also have occurred on a near vertical fault plane and that the total 

 earthquake phenomenon may have been a comptex combination of the mechanisms 

 envisioned by Press and Plafker. 



It should be recorded that Furimoto (1965), using the "directivity 

 function" method of Ben-Menahem (1961) and the data of the seismograph 

 station at Kipapa, Hawaii, arrived at a rupture length of 8OO kilometers 

 for the Alaskan Earthquake, a rupture velocity of 3 kilometers/second. 



27 



