802 NAFE AND DRAKE [CHAP, 29 



velocities in a sample of Globigerina ooze compressed between porous disks. 

 Shear waves were observed at pressures above 500 kb/cm^ on the initial 

 compression. On decompression shear waves could be identified at pressures as 

 low as 64 kg/cm^. Indirect evidence from seismic refraction measurements for 

 the existence of shear waves in marine sediments has been reported by Nafe and 

 Drake (1957). An excellent measure of an average sedimentary shear-wave 

 velocity is to be found in the dispersion of oceanic Love waves and higher mode 

 Rayleigh waves. The observed periods and low values of group velocity near the 

 group velocity minimum cannot be accounted for without assigning a rigidity 

 to the sedimentary column. According to Oliver and Dorman (Chapter 8) 

 an average shear velocity between 0.25 and 0.60 km/sec is required. 



D. Dispersion Analysis 



Surface waves traveling in a layered half space are, in general, dispersed 

 with phase and group velocity determined by the depth variation of elastic 

 wave velocities and density. Normal mode propagation in shallow water, and 

 Rayleigh and Love waves in the crust and upper mantle of the earth are familar 

 examples of such dispersed wave trains. The dispersion may be computed from 

 an assumed structure. By comparison of observed with computed phase and 

 group velocities the validity of the assumed velocity-density depth variation 

 may be tested. A comprehensive treatment of layered media is to be found in 

 Ewing, Jardetsky and Press (1957). 



There are numerous examples of dispersion studies relating to shallow- 

 water sediments. Pekeris (1948) has computed dispersion for a number of 

 two- and three-layer cases, each layer being assumed liquid and of constant 

 density and velocity. Press and Ewing (1950) and Tolstoy (1954) have treated 

 the case of a liquid over a semi-infinite elastic solid. Tolstoy (1960) and Sato 

 (1959) have considered cases of continuously varying material properties. 



The most detailed dispersion studies involving properties of sediments apply 

 to shallow water. Some work yields information on deep-water sediments. 

 Oliver et al. used the fluid thickness indicated by Rayleigh-wave dispersion 

 across ocean basins to estimate average sediment thickness. Katz and Ewing 

 (1956) identified a constant-frequency arrival occurring on deep-water refrac- 

 tion records at ranges of the order of 60 km as a wave propagating for part of its 

 path in a thin layer just below the water-sediment interface with a velocity 

 lower than that in the water. Much more information on deep-water sediments 

 may be expected in the immediate future as machine computations of dispersion 

 for a wide variety of assumed structures become available for comparison with 

 observations. 



E. Thermal Conductivity 



Thermal conductivity has been measured both by steady-state and transient 

 methods. Ratcliflfe (1960) described apparatus for steady-state measurements 



