SECT. 1] 



THE TTN CONSOLIDATED SEDIMENTS 



79 



reflection curves as would be the case if they are associated with the same 

 interface. Certainly it is possible that two interfaces are present ; the upper 

 one producing reflections but no refractions and the lower one producing 

 refractions but no reflections, but this seems an unlikely interpretation. In 

 order for the extension of the refraction lines to be tangent to the Rn curve, 

 they would have to curve downward in the manner indicated by the dashed 

 lines, indicating a gradient below the 2-3 interface. The fact that the outer 







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Fig. 5. Seismic records showing critical angle reflections for Rn- Rm arrivals are from 

 base of low-velocity sediments. Water depth = 3.75 km. Thickness of low-velocity 

 sediments ~ 4 km . 



portions of the G2 lines are observed as straight lines indicates that at 

 some depth below the 2-3 interface, the velocity becomes constant or nearly 

 so. 



The 2-3 interface is judged to be a discontinuity with the higher velocity 

 below on the basis of the observation of a critical angle for reflections from it. 



