110 



T. I. Oblogina 



the impression, that in the vicinity of this point the detectors are 

 connected to the -wTong poles (Fig. 6). In Fig. 7, a and 6, we show 

 a seismogram on which a refracted wave is followed in the first onsets and 

 a diffracted wave in the last. As can be seen, a phase inversion occurs in the 

 region of markers 70.96-70.45. The smaller the spread, the more marked 

 is the phase inversion near the point of tangentionality. 



2-2 



2-1 



2-0 



UXLi 



0-2 0-4 0-6 0-8 1-0 1-2 



K, km 



Fig. 8. Observed dyuamic hodographs of a diffracLed wave along longitudinal profiles. 



Dynamic hodographs were constructed for the diffracted waves observed. 

 An example is given in Fig. 8. Here, as usual, distances from the shot point 

 are plotted along the .%-axis and time along the 3'--axis. The amplitudes of 

 the diffracted wave were plotted from the points of the ordinary Idnematic 

 hodograph t = t{x). The dynamic hodographs show that the intensity of the 

 diffracted wave increases as the wave approaches the point of tangentionality 

 we have referred to, and that phase inversion occurs in the neighbourhood 

 of this point. 



THE DYNAMIC PROBLEM OF DIFFRACTION FROM THE 

 EDGE OF A "TAPERING STRATUM" 



Formulation of the Problem — • Let us take two media made up of two 

 elastic liquids separated by a plane boundary. The upper medium is 

 characterized by the velocity l/a^ = ]/ (Aq/^q), and the lower one by 

 I/cq = y (^i/^i), where 2.q and /Ij are the elastic constants and ^q, q^ 

 the densities of the media. We shall assume that the velocity in the 

 upper medium is lower than in the medium which is underneath it. 



