MULTIPLE REFLECTED WAVES 



81 



of the corresponding properties of the reflecting boundaries by using multiple 

 waves. Conversely, we can determine the arrival direction at the beginning 

 of the path from the arrival directions of waves mukiplied an even and 

 an odd number of times. A more comphcated phase inversion may occur 

 in the propagation of partially multiplied waves because both the lower 

 and the upper reflecting boundaries may be dissimilar as to the direction 



28 



32->^ 



34 



36- 



4 



Fig. 4. Records of multiple reflections obtained by modelling. 



in which wave resistance alters as the waves pass through them. In such 

 a case one must consider only the number of reflections from boundaries 

 where wave resistance decreases as the wave passes through, and allow for 

 the difference in arrival direction at the beginning and at the end of the 

 path after an odd number of reflections from such boundaries. 



Some investigators attribute the change in arrival direction which accom- 

 panies a change in the number of multiples to interference reflected from 

 the base and top of a thin layer with a thickness less than half the principal 

 wave length. 



Applied geophysics 6 



