DIFFRACTED SEISMIC WAVES 119 



the interface and the distance h from the "tapering stratum" to the inter- 

 face. 



Figure 11 shows two theoretical seismograms of the horizontal and vertical 

 displacements of a diffracted wave in a case where a wave incident on the 

 edge of a "tapering stratum" has the shape of a smooth alternating pvdse. 

 The same values have been taken for all the characteristics of the medium 

 as were taken in calculating the dynamic hodographs. The shape of the 

 diffracted wave can be seen on each trace. The dominant period of this 

 wave {Tp = 0.04 sec) is greater than that of the incident wave {T = 0.03 sec). 

 Moreover, with the given shape of the incident wave, both its extremal 

 values — the first and second— are identical. The value of the first extreme 

 for the diffracted wave, however, is greater than that of the second, so that 

 in the given case this wave is characterized by a less symmetrica] vibration 

 shape. 



SUMMARY 



Comparison of the experimental and theoretical findings set out above 

 yields the following conclusions. 



1. Minima on the direct and inverse hodographs of a diffracted wave 

 correspond to one and the same marker on the profile. 



2. The amplitudes of the diffracted wave increase along the profile as this 

 wave approaches its point of contact with a refracted Avave. 



3. The diffracted wave suffers phase inversion in the neighbourhood of 

 this point of contact. 



REFERENCES 



1. I. S. Berzon, Some problems in the kinematics of propagation of diifracted seismic 



waves. Tr. geofiz. in-ta Akad. Nauk SSSR, No. 9 (1950). 



2. G. A. Gamburtsev, et al. The Refracted Wave Correlation Method. Izd. Akad. Nauk 



SSSR (1952). 



3. A. M. Yepinat'yeva, Some types of diffracted waves recorded in the course of seismic 



observations. Izv. Akad. Nauk SSSR, ser. geogr. i geofiz., 14, 1 (1950). 



4. T. I. Oblogina, a local representation of a system consisting of a head wave and 



a sliding wave. Vestn. MGU {Univ. Moscow), No. 1, (1956). 



5. V. I. Smirnov and S. L. Sobolev, Tr. Seistnol. in-ta No. 20, Izd. Akad. Nauk SSSR 



(1932). 



6. P. T. SoKOLOV, Physical and Theoretical Foundations for the Seismic Method of 



Geophysical Prospecting, GONTI (1933). 



7. S. L. Sobolev, Tr. Seismol. in-ta. No. 41, Izd. Akad. Nauk SSSR (1934). 



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Tr. Tbilisskogo geofiz. in-ta, 2 (1937). 



