30 V. P. G6RBATOVA 



(a) the influence of the velocities at which transverse waves are propagated 

 on the intensity of longitudinal primary waves; 



• (b) the effect of adding an ith. layer, and changing the longitudinal velocity 

 in it, on the intensity of the head waves excited in layers of greater depth; 



(c) the effect of a sharp principal refracting boundary on the intensity 

 of a head wave excited in it; 



(d) the damping of the head waves with distance and the influence of the 

 bedding depth of the main refracting boundary on the intensity of these 

 waves. 



We shall examine all these questions in order. 



(a) Formula (2) is used to determine the intensity of the head waves 

 excited in multi -layer media. As has been shown above the multipHer Co as 

 well as the coefficients of refraction (P,Pj.j.j) (P,-^jPj) at all the intermediate 

 interfaces depend only slightly on the parameters y and A, that is on the 

 values of the transverse velocities in the covering layer. The intensity of the 

 the head waves is consequently also only slightly dependent on them. It 

 follows that ignorance or inaccurate knowledge of the transverse velocity 

 values in the covering layer is not an obstacle in the way of calculating 

 the intensities of the longitudinal head waves excited in deep boundaries. 

 In drawing this conclusion we are assuming that the covering layer is charac- 

 terized by the parameters indicated in the introduction. 



The transverse velocity values in layers directly adjacent to the principal 

 refracting boundary, on the other hand, may well exert a considerable influence 

 on the hitensity of a head wave excited at this interface. The curves in Fig. 4 

 show at a glance the possible variation in the theoretical intensity of a head 

 wave according to the assumptions we make about the ratio between the 

 transverse and the longitudinal velocities in the adjacent layers, on the 

 boundary of which the primary wave under consideration is formed. 



It can be seen from the curves that the wave intensity increases in inverse 

 proportion to the parameter A and in direct proportion to the parameter y, 

 which characterize the adjacent layers on the boundary of which the head 

 wave forms. 



This means that in order to calculate the intensity of the head waves, 

 we must have information about the densities and the values of transverse 

 and longitudinal velocity on both sides of the interface where the head 

 wave is excited, and that we must also know the values of velocity for the 

 longitudinal waves and the densities throughout the covering layer. 



(b) We shall now see how the intensity of the refracted waves varies if 

 the longitudinal valocity value changes in one of the upper layers, other 

 than the topmost, which is not directly adjacent to the interface at which 



