274 



HEKZKN AND MENARD 



[chap. 12 



-lOOO FATHOMS 

 -1500 



1500 



2000 



~ 2500 



2000 



- 2500 



1500 



2000 



I I I I I M I I I I I I I I I I I I I I I I 



. 30 40 



I I I I H I I I I I I I M I I I I I |l I I I [ I I I I I I I I I I I I I I I I I I I I I I I I I 



~_60_ , 70 80 90 100 



„,, ,30 40 50 60 70 80 90 100 " 



' I ■ ' ' ' ' ' I I I I I I I I ' ' ' I " ' I I I I ■ ■ I ' ■ " I " ' ' I ' ■ ■ ' I ' I ' I ^ ' ' ■ ' I ■ " I ! " ' . I ■ I ' ■ I I ' ■ . ^. . . ' I ■ . I_ 



< 1400 



>2000 FM 



•.-.EARTHQUAKES 



Fig. 35. Mifl-ocoanic ridge and rift valley in the southwest Indian Ocean. (After Ewing 

 and Heezen, 1960.) 



ocean basin has a median line in addition to the one for the whole basin. The 

 great curve bounded by New Guinea, the Philippines and Japan is an example of 

 such a convexity in the Pacific. This method of geometrical construction shows 

 that the crest of the " East Pacific " Rise (part of which is also known as the 

 Easter Island Ridge) lies near the median line between New Zealand and Antarc- 



