Chap. 12] 



MISCELLANEOUS GEOPHYSICAL METHODS 



925 



distance between the vibrator and a given detector is s, if a surface layer 

 with the wave velocity Vi is underlain by another layer with the velocity 

 V2 at the depth d, and if the assiimption is made that the waves travel 



PHASE SPEED 





S^";'' 



' AMPLITUDE \ 

 DISTANCE CURVES" 



82 



O 



id 



DISTANCE IN FEET 



FiQ. 12-21'. Phase-speed and amplitude-distance curves. 



vertically to and from the second layer, the phase difference between the 

 surface wave and underlayer wave is 



A<p = — + s(-— -), 



Vi \V2 Vi/ 



(12-12) 



