PACIFIC SUBMARINE PROVINCES 



531 



tween Japan and the equator is rotating clockwise. The evidence lies in 

 the study of several great earthquakes in the region and in the geology 

 of known faults in the Philippines and Japan. 



Whether or not the entire Pacific is moving counterclockwise, the 

 problem arises along the North American margin: What is the relation of 

 the dextral Pacific movement to the fracture zones? In a personal com- 

 munication on the subject Dr. Benioff comments as follows: 



I assume as a working hypothesis that the radial movements at the continental 

 margins are expressions of growth of the continents by accretion of material 

 from below by unknown processes. As the continents rise, the margins are 

 driven over the adjacent oceanic masses by gravity as mentioned in my paper 

 on the fault origin of oceanic deeps (Benioff, 1954). In general, the movement 



is thus normal to the trend of the coastline. On this basis the curvature ot the 

 San Andreas system and the existence of the Garlock Fault are the result of 

 differential expansion of the continent at the Pacific margin — with the northern 

 portion expanding faster. 



The movement along the Garlock Fault is sinestral, whereas the movement 

 on the Murray fracture, given by Mason's magnetic surveys, is dextral. More- 

 over the Mendocino fracture appears to have no expression within the conti- 

 nent east of the San Andreas Fault. I am inclined therefore to the opinion that 

 these oceanic fracture systems are unrelated to the systems shown in my figure 

 [Fig. 32.19, this book]. They are probably older — or at least no longer active 

 since they have no earthquake activity of consequence except in those portions 

 adjacent to the continental margins where it is probably induced bv the move- 

 ments going on there. It would seem to me that if the oceanic fracture svstems 

 were closely related to the present radial flux pattern they should be active 

 seismically over most of their lengths. 



