and 



l/2(V p /V s ) 2 -l 

 ° (V p /V s )2-1 



K = p(V p 2 - (4/3)V s 2 ) 



Ud = pv s 2 



E d = 2y d (l+o) 



The above relationships between elastic moduli and compressional and 

 shear wave velocities are not entirelv valid for marine sediments since 

 they are not truly elastic. However, if it is desirable to determine the 

 dynamic elastic properties of the material at the frequency of the seismic 

 wave, as in the vibratory testing of foundations for machinery or runways, 

 the above equations are precise (Meidav, 1962). 



When long-term static loading of unconsolidated material must be con- 

 sidered, the rheological effects of creep and flow must be taken into 

 account if the response of the body to stresses is to be completely speci- 

 fied (Meidav, 1962; 1960). This would require the inclusion of one or 

 more viscosity coefficients describing the behavior of the material under 

 low frequency or static conditions. 



This frequency effect upon the rigiditv coefficient is similar to 

 the response of water to shear waves. At low frequencies, shear waves 

 will not pass through the water because of near zero rigidity: however, at 

 megacycle frequencies, shear waves do propagate because of a finite, 

 discernible rigiditv. 



Meidav (1960; 1962) considers the standard linear solid a better 

 model of the stress-strain relations in the earth, i.e., 



°+T f -Uo<«*Tl£) (24) 



where o = stress 



e = strain 



T Q ,T]_ = relaxation time 



u = operator dependent upon the type of wave 

 used 



The ratio of phase velocities in a standard linear solid/elastic is 

 given by (Meidav, 1962) 



16 



