SPATIAL PROBLEMS IN GEOMETRICAL SEISMICS 



59 



(c) Construction of the trace of the intersection between the observation 

 plane and the ray surface after reflection. For this purpose we plot on the 

 plan projections of the reflected rays according to their known azimuths 

 (these are shown in Fig. 4 by the lines 5). As can be seen from the illustration 

 the direction of the projection of the incident ray coincides with the direction 

 of the projection of the reflected ray only along two azimuths (0° and 90°)^'^\ 

 In neither case is there any azimuthal deviation; in all the remaining cases 

 azimuthal deviations are observed and the projections of the rays are not 

 straight lines but are broken lines consisting of two parts. 



At the point of reflection then the ray suffers an azimuthal deviation 

 which is easily visible when we project the ray onto the horizontal plane 



340 



350 10 



330 



320. 



310^ 



300^ 

 290/ 

 280 J 



20 



30 



40 



.50 



,60 



JO 



270 



2601 



250> 



9«- 



6A 



I 



<J8- 



,80 



90 



100 



240' 



230^ 



220 



210 



200 



120 



130 



140 



150 



160 



190 



180 l"^0 



o -2 

 * -3 



Fig. 7. Determination of the direction of the rays after reflection by means of a Wulff net. 



1 — direction of incident rays with azimuths 0-90° at every 10°; 2 — direction of 



reflected rays; 3 — direction of the normal to the interface at the point of incidence 



of the corresponding ray. 



