Chapter 3 



MULTIPLE REFLECTED WAVES 



S. D. Shushakov 



In seismic prospecting, the separation and tracing of useful waves may be 

 made difficult by interference from multiple reflected waves. These can also 

 be mistaken for single waves and so give rise to errors in interpretation. 



Although much has been written on the study of multiple waves the 

 difficulties of recognizing them remained, and in the course of a seismic 

 prospecting operation they are sometimes mistaken for single waves. 



The present article describes the results obtained fronr modelling multiple 

 reflected waves and gives a number of theoretical calculations performed 

 according to the contour integrals method. The main topic is a description 

 of the longitudinal waves which are commonly encountered in seismic 

 prospecting work. Certain features of multiple reflected waves are noted and 

 practical suggestions are put forward. 



Multiple reflected waves of one intensity or another probably occur in 

 all, or nearly all regions. In discussing the problems connected with multiple 

 waves the term is frequently applied to those waves which are clearly 

 <listinguishable and consequently possess an intensity commensurate with 

 that of single reflected waves wdtli approximately the same transmission 

 times as the multiple waves. Reviewing the seismological conditions which 

 prevail in regions w"here multiple waves of such intensity are observed, 

 we may conclude that the follo^ving special conditions which favour the 

 formation of such waves are found in these regions: 



(1) a small number of interfaces characterized by comparatively high 

 reflection coefficients; 



(2) comparatively poor damping of the waves between these interfaces. 

 In the region Leningrad Station of the Krasnodar district, for example, 



there is a layer of highly wave -resistant Cretaceous deposits wdiich is a re- 

 flecting horizon for multiple waves. In the outer zone of the Cis-Carpathian 

 depression, a gyp svun -anhydrite horizon from which multiple waves are 

 reflected can be distinguished by its wave resistance. In north-western Ger- 

 many the lower boundary is formed sometimes by the Cretaceous cover, 

 sometimes by a combination of this with one of the intermediate boundaries 

 which has a high coefficient of reflection'^^'. In other regions such bound- 



