• Continuous reflection profiling and associated measurements with expendable 

 sonobuoys furnish data critical to underwater acoustics in two categories (for a given area 

 or, in the general case, for prediction): (a) the form and true thicknesses of sediment and 

 rock layers, and (b) the presence and values of velocity gradients. Specifically, data are 

 furnished for several areas in the Northeast Indian Ocean. 



• Statistical studies of velocity gradients in silt-clay sediments will allow pre- 

 diction of sound velocity versus depth in the sea floor and the presence and values of 

 velocity gradients in similar sediments in the world's oceans. Specifically, data in 17 

 areas of the world's oceans were averaged and a regression equation furnished for the 

 velocity gradient, a, given one-way travel time, t (a = 1.316 - 1.1 17t)(see Figure 6, p. 34). 



• Results of studies of the attenuation of sound were as follows: 



1 . Twenty-six new published values of the attenuation of compressional 

 (sound) waves in marine sediments complement and supplement older data and support 

 the conclusion that sound attenuation is approximately dependent on the first power of 

 frequency. 



2. New data support the conclusion that relations between sound attenua- 

 tion and sediment properties allow prediction of attenuation when mean grain size or 

 porosity are known. 



3. A special study of sound attenuation versus depth in sands, silt-clays, 

 sedimentary rocks, and basalts should allow generalized predictions of attenuation in 

 these various layers in the sea floor. 



• Results of studies of variations of sediment density and porosity versus depth 

 in the sea floor were as follows: 



1 . Data from the Deep Sea Drilling Project were combined with other 

 information to produce diagrams, curves, and regression equations of laboratory values 

 of density and porosity versus depth in the sea floor for common sediment types. 



2. The amount of volume increase (elastic rebound) from borehole to 

 laboratory, caused by release from sediment overburden pressure, was estimated from 

 soil mechanics tests. Maximum values of such rebound are about nine percent in silt- 

 clays from depths of 600 meters. Rebound is less in other sediment types. 



3. When percent rebound in porosity is deducted from laboratory porosity, 

 an estimate of the in situ porosity (and density) is determined. 



4. These data allow generalized curves and regression equations for density 

 as a function of depth in the sea floor from which predictions can be made. 



• Results of studies of shear wave velocities versus depth in marine sediments 

 were as follows: 



1 . Twenty-nine in situ measurements of shear wave velocities in sands to 

 12 meter depths indicate (in these sands) that Vg = 1 280^-28; where Vg is shear wave 

 velocity in m/s, and D is depth in meters. 



