Nafe and Drake (1957) compiled indirect information on shear wave 

 velocities in marine sediments from seismic refraction measurements 

 (Figure 8) . 



More recently, Auld et al. (1969) have measured average shear wave 

 velocities of marine sediments off northern California using an ocean 

 bottom seismometer. The resulting values are 0.34-0.40 km/sec for the 

 average shear velocity, results which are consistent with values obtained 

 in earlier studies to explain the dispersion of oceanic surface waves 

 (Sykes and Oliver, 1964; Oliver and Dorman, 1961). 



Swain (1962) , in an engineering site evaluation study for the Ray 

 Area Rapid Transit Tunnel in San Francisco Bay, used seismometers in bore- 

 holes to arrive at in-situ values of shear velocity- The in-situ values 

 differed substantially from the values measured on cores taken at the same 

 locations. 



The shear wave velocity data, therefore, are meager. It is strongly 

 suggested that research into the methods and the feasibility of shear wave 

 velocity measurements in marine sediments be undertaken because of the 

 enormous engineering significance of these data. 



Elastic Moduli and Acoustic Velocities . The relationship between 

 elastic moduli and longitudinal and shear velocities are 



Vr, = 



Ed (l-o) /K +(4/3)y d 



P / p(l+o)(l-2o) /' P (22) 



V„ = 



^d 



2 (1+ ) / p (23) 



where V = compressional wave velocity (cm/sec) 



V = shear wave velocity (cm/sec) 



o = Poisson's ratio 



K = bulk modulus or incompressibility 

 = 1/6 (dynes/cm^) 



8 = compressibility 



Mj = dynamic ridigidy (shear modulus) (dynes/cm^) 



E^ = modulus of elasticity (Young's Modulus) 

 (dynes/cm^) 



p = saturated bulk density (gm/cm ) 



15 



