where p = p w n + p s (l-n) 



r = correlation between V and n 



For marine sediments, relationship between sound velocity and porosity 

 has received considerable attention (Hamilton et al. , 1956; Sutton et al. , 

 1957; Nafe and Drake, 1957; Horn et al. , 1969). The general conclusion 

 is that sound velocity increases as porosity decreases. Most researchers 

 agree, however, that porosity in itself may be a first approximation of 

 a number of interrelated physical properties that, when combined, affect 

 the sound velocity in sediment. A typical trend of sound velocity relative 

 to porosity is shown in Figure 4. 



Since moisture content and void ratio of saturated sediments are func- 

 tions of available pore space, the curves of these properties should show 

 trends similar to that of porosity when plotted against sound velocity. 

 Figures 5 and 6, taken from Horn et al. (1968), illustrate these trends. 



Additionally, there is a positive correlation between wet density 

 and sound velocity in water-saturated sediments — sound velocity increases 

 with increasing wet density (Horn et al., 1968; Sutton et al. , 1957; Nafe 

 and Drake, 1957). This correlation is shown in Figure 7. 



There is, therefore, a correlation between the acoustic and some 

 physical properties of marine sediments. The higher the porosity, mois- 

 ture content, and void ratio, the lower is the sound velocity. Increases 

 in wet density are matched by increases in acoustic velocity. There is, 

 however, no readily apparent correlation between sound velocity and dry 

 density, carbonate content or, most unfortunately, shear strength (Horn 

 et al., 1968). 



When sediment shear strength is plotted against sound velocity, the 

 data fall into groups which reflect the mean grain size and sediment 

 origin. Although shear strength is not considered to be a reliable index 

 of the acoustic properties of marine sediments (Horn et al., 1968), there 

 is, generally, an increase in sound velocity as shear strength increases. 



Grain size is the most important physical property in determining the 

 acoustic properties of marine cores (Horn et al. , 1968). For example, 

 turbidites have high velocities, ash layers have intermediate velocities, 

 and muds and clays have low velocities. 



Acoustic compressional velocity data may provide an estimate of the 

 facility with which materials may be excavated, i.e., the rippability 

 (Patterson and Meidav, 1965). Granites, for example, have acoustic 

 velocities higher than limestone, and limestone has velocities higher 

 than those in unconsolidated sediments. 



13 



