MULTIPLE REFLECTED WAVES 77 



These boundaries are usually denoted as follows: the Earth's surface, or the 

 base of the low-velocity zone, by the index zero*, and other boundaries 

 which reflect the multiple wave by the indices 1, 2, ... m, in order from top 

 to bottom. An interbed echo reflected from some boundary denoted by 2, 

 from the base of a weathered zone and from some intermediate boundary 1, 

 is denoted as 201 ; a fullpath echo reflected n times from a lower boundary 1 

 and 71 — 1 times from the zero boundary is denoted as 10 ... 101. 



Fig. 1. Records of multiple reflections obtained under natural conditions. 



Different types of multiple reflections have certain different kinematic 

 properties. Full-path multiple waves 10 ... 101 appear as single waves 

 reflected from interfaces which lie deeper than the boundary from which 

 they are in fact reflected. Fig. 2 shows a schematic diagram of multiple 

 wave rays, together with the disposition of the actual reflecting boundary 

 .and a number of fictitious boundaries which could be constructed if one 

 mistook these waves for single ones. If the real boundary 1^ is inclined at 

 an angle y to the zero surface, then a double reflected wave will appear as 

 a single wave reflected from the false boundary Ig, which acts as a mirror 

 image of the zero boundary in boundary 1^ and is inclined at an angle of 2^. 



A boundary 1„ is inclined towards the zero boundary at an angle n^. 

 If the depth of the boundary Ij along the normal to it below the shot point 

 is equal to H^, then the depth of a boundary along the normal to it below 

 .the same point is given by 



^ ^ m\y ^ ' 



* Henceforth called the zero surface or boundary. 



