The sound velocity values thus far determined were direct measurements using 

 an Underwater Systems, Inc., sediment velocimeter, model no. USl-101, on loan 

 from NAVOCEANO. These values will soon be compared with those determined by 

 four sources discussed below. 



a. Direct measurements are being made at the URI laboratory by using a longi- 

 tudinal wave vibration apparatus (Fig. 2) . This device utilizes an air chamber to 

 provide confining pressure, ceramic transducers placed at both ends of the sample, 

 an oscillator, a pulse generator, an amplifier, and an oscilloscope. The wave forms 

 are displayed on the oscilloscope and can thus be measured in time units. The velocity 

 is computed from the time value and the known length of the sample. This apparatus 

 will soon be modified to provide water as the confining medium. 



b. A table of estimated sound velocities was constructed to relate porosity, 

 density, and median grain size to sound velocity. This table is a compilation of pub- 

 lished reports in which the values of all these properties are given, Hamilton, et al. 

 (1956), Laughton (1957), Sutton (1957), and Shumway (1960), and was tabulated irre- 

 spective of physiographic province or soil type. 



c. Using most of this same data, M. McDonald (1965) categorized the source 

 areas into shelf, slope, shelf-slope, deep, and slope-deep provinces. He then 

 ran a regression analysis on the data to determine the significant variables affecting 

 the sound velocity value for a given province. 



d. Sound velocity was computed from laboratory elastic moduli determinations. 

 This technique will be discussed in the following section. 



All these sound velocities will then be used in the mathematical model to note their 

 effect on the impedance layering and consequently on the value of reflection coefficents. 



In order to understand the acoustic properties of the sediment aggregate, the 

 elastic qualities of the mass must also be examined. Therefore, a more intensive 

 treatment of analysis was given to core no. 2 of the TOTO cores as a pilot study, to include 

 the determination of several elastic moduli by various techniques . This experiment will be 

 performed on the remaining core samples and on ensuing samples. 



Elastic Moduli Experiments 



The behavior of soil under seismic forces, vibrations, or dynamic loadings 

 is dependent upon some soil properties and loading conditions. An experimental study 

 on dry Ottawa sand and saturated calcium carbonate clay (core no. 2 of the TOTOcore^ 

 revealed some relationship and some validity to the elastic theory. From this study 

 there is reason to believe that a field soil modulus type of test can be used to deter- 

 mine field sound velocities. 



381 



