REFRACTED AND REFLECTED LONGITUDINAL WAVES 41 



(b) the influence of the overall depth of the reflecting boundary and the 

 ratio between the thicknesses of the different layers on the intensity of re- 

 flected waves over a shot point; 



(c) comparison of the intensities of single and double echoes above a shot 

 point. 



We shall take these problems in the order given. 



(a) The intensity of reflected waves in multi-layered media is determined 

 from formula (3) and above a shot point from formula (11). Formula (11) —and 

 so also the intensity of reflected waves above a shot point — do not depend 

 on the transverse velocities in the media under consideration. In formula (3) 

 only one coefficient of reflection depends on the transverse velocity values. 

 When the reflection is from an interface with high acoustic rigidity, it 

 depends mainly on the ratio of transverse to longitudinal velocities in the 

 layer from which the reflection takes place; when the reflection is from an 

 interface with lower acoustic rigidity the coefficient of reflection depends 

 on the transverse velocity values on both sides of the reflecting boundary. 



The curves (see Figs. 5, 6 and 7) show the dependence of the coefficient 

 of reflection (and therefore also the intensity of the echoes) on the trans- 

 verse velocity value at the reflecting boundary. The echoes are more in- 

 tense the smaller the parameter A at the reflecting boundaries, while for 

 waves reflected from media with low travel velocity the intensity of the 

 waves increases (when A is fixed) with increase of v. The influence of the 

 transverse velocities on the intensity of the echoes is greater for multiple 

 echoes. 



It is becoming clear that to determine the intensities of echoes in multi- 

 layered media we need information only about the values of the transverse 

 velocities at the actual reflecting boundary. If the refle tion occurs from 

 a high velocity layer we must take the value of transverse velocity in the 

 layer under the reflecting horizon; but if reflection takes place from a wea- 

 thered layer we need to know the transverse velocity on both sides of the 

 reflecting boundary. What has been said holds true for media with the 

 above-mentioned parameters when the angles at which the waves strike 

 the reflecting boundaries are lying within the limits indicated. 



(b) The intensity of reflected waves above a shot point is determined 

 from formula (11). From this formula it is clear that if the depth of the 

 reflecting boundary increases or diminishes n times the thickness ratio for 

 the different layers, and h^^ remaining as before, then the intensity of the 

 echoes above the shot point -will diminish or increase n times. If the velo- 

 city and density-structure of the medium are unchanged and the depth 

 of the reflecting boundary is also unchanged, the intensity of the waves 



