88 



RAITT 



[chap. 6 



the Cambridge University Department of Geodesy and Geophysics (Gaskell, 

 Hill and Swallow, 1958). It illustrates a very clear-cut example of the second 

 layer at a Pacific station which is more conspicuous than the average station 

 because of the thin sediment, 0.05 km, and the unusually thick Layer 2, 

 2.7 km. Layer 3 is well observed, but penetration to Layer 4 was not achieved. 



20n-r 



['III' 



Profile 2; 1956 cruise 



M I I I I I I I I I I I I I i 



M { I I I I I 1 i I I I 



I I I I I I I I I 



Beor 

 N 



10 15 20 25 30 



Direct water wave time (sec) 



I ' I I I ^ I I I I I I I ill I I I J_i I I 



35 40 45 



Atlantis 

 S 



9 17,000 

 ^ 18,000 

 g- 19,000 



Q 



"Atlantis 



10,000 - 



- 20,000 



Q. 



Q 30,000 



40,000 



10 



20 



— I \ r- 



30 40 



Distance (km) 



Ocean 



177 



5 96 



693 



7.93 



50 



— 1 1 1 



60 70 



Q. 

 Q 



10 



15 



50,000'-- 



Fig. 5. Travel-time plot of Atlantifi Bear profile 2, 1956 cruise. Laj'er 2 velocity = 5.96 

 km/sec; Layer 3 velocity = 6.93 kin/sec; Layer 4 velocity = 7.93 km/sec. (After 

 Oflicer et al., 1959.) 



Fig. 3 represents another station of the Cambridge group, this one also 

 taken by H.M.S. Challenger in the Atlantic. It also gives a good example of 

 Layer 2 because of its fairly great thickness, 2.3 km. The length of the Layer 3 

 segment is shorter than in Fig. 2 but long enough to give a good demonstration 

 of the Layer 3 velocity, 7.10 km/sec, and to determine the Layer 2 thickness. 



