be encouraged, is by use of velocimeters lowered from the 

 surface. In the future, a promising field of research may- 

 be concerned with the microvelocity structure in the water 

 a few meters and tens of meters above the sea floor. In 

 situ measurements from deep-diving research submersibles 

 hold much promise for such studies. * 



Temperature gradients within the sea floor vary 

 enough from place to place to affect the vertical variations 

 of sound speed; this value must be known in order to esti- 

 mate vertical sound-velocity gradients. 9 Such data can be 

 obtained for general regions (and some particular regions) 

 from the heat-flow measurements currently being taken by 

 geophysicists in ocean basins. 



It is known that sediment overburden pressures affect 

 sound speed and other elastic properties in several ways -- 

 for example, by reduction of porosity, by pressure- 

 chemical effects (inducing more "cementation"), and by 

 inducing a more rigid sediment structure through grain-to- 

 grain pressure. 



Anywhere an oil-well type of hole is drilled into the 

 sea floor, an attempt should be made to determine the 

 vertical sound-velocity gradients by well-logging, a standard 

 technique in the oil exploration industry. This was tried, 

 but not accomplished, in the preliminary Mohole drilling 

 operations at the Guadalupe site. Production of more valid 

 geoacoustic models of the sea floor is certainly one by- 

 product to be expected from future holes drilled by the 

 Mohole Project. 



LaFond, Mackenzie; personal communication. 



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