96 S. D. Shushakov 



where y' is a fictitious angle of incidence computed from the section con- 

 structed. 



After this formula (1) can be used to calculate the depth H^ along the 

 normal to this boundary and to construct the cross-section for the boundary. 

 For different multiple waves and under different seismic and geological 

 conditions, there may be a different answer to the problem of interpretation. 

 Accuracy may vary and may more or less satisfy practical requirements, 

 just as in the case of single waves. 



In elaborating methods for using multiple reflections a problem which 

 may arise is how to use these waves to separate, in the cross -section, the reflec- 

 ting boundaries which have the highest reflection coefficients, with the result 

 that multiple waves are reflected from these boundaries. The identification 

 of such boundaries can help to improve the geological interpretation of 

 seismic observations. 



For this purpose we can use the determination of effective velocities 

 from the hodographs of certain multiple reflections, such as the hodo- 

 graphs of the most distinct full-path echoes. In order to use these velo- 

 cities we must determine the kind of boundaries these waves are reflected 

 from. 



For purposes of geological interpretation, it is possible to use the relationship 

 ^lescribed in the foregoing sections, between the directivity of vibrations 

 with different numbers of multiples and the combination of properties in 

 the boundaries from which they are reflected; we can also use the shape 

 characteristics of the graphs representing the variation in intensity or form 

 of the record for multiple waves with distance from the source and with 

 increase in the number of multiples. 



PRINCIPAL CONCLUSIONS 



Multiple reflections can interfere considerably with the recognition and 

 tracing of single reflections and — under certain conditions — refracted 

 waves. This is particularly true when the interfaces from which these waves 

 are reflected are at shallow depths. Moreover, they can be taken for single 

 reflections and so give rise to errors in interpretation. 



At the same time, under certain conditions multiple reflections can be 

 used in seismic prospecting, especially in regions where these waves 

 predominate over single waves which have nearly the same travel times as 

 their own. 



So far, however, insufficient work has been done on elaborating methods 

 for recognizing multiple reflections, Recognition by kinematic indications 



