632 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



presented by Benioff and depicted in Chapter 32, the Denali fault is 

 presumed to be of right-lateral strike-slip movement, and to have trans- 

 lated rocks 150 miles along the fault. 



The principal evidence for right-lateral slip, other than the possibility 

 of the existence of a great fault with smooth arcuate curvature is that of 

 first motion seismograms, and these, according to St. Amand, "indicate 

 that the north Pacific Basin, from Baja California to the Kurile Islands at 



least, is and has been for a long time, rotating counter-clockwise." 



Not much can be said to resolve the problem. St. Amand's interpreta- 

 tion may serve to evoke careful observation of the fault features by those 

 who work in the field along them, and eventually it may be said either 

 that horizontal motion has or has not been appreciable. It may be noted 

 that the other great fault zones of the system were not recognized by St. 

 Amand. 



