892 EXPLORATION GEOPHYSICS 



the interpreter of seismic data should keep in mind the possibiHty (and 

 probability) that multiple reflections may be present on the record.f 



There are many examples of multiple reflections in the literature of 

 general earthquake seismology, as refracted waves are reflected once or 

 more by the surface of the earth. Very seldom, however, have illustrations 

 been published of multiple reflections in seismic exploration. Perhaps this 

 is due to the fact that they have not been recognized by the interpreter, or, 

 if recognized, have been discarded as anomalous due to their abnormally 

 steep dips. 



In order to illustrate the general theory, we may consider two simple 

 cases of multiple reflections : ( 1 ) between a shallow reflecting bed and the 

 surface of the earth, and (2) between two reflecting beds. Each of these 

 two cases may be solved by the theory of images. 



\l / 



i 



Fig. 562. — Multiple reflections between surface of the earth and a reflecting horizon. 



Figure 562 illustrates a simple case of a multiple reflection occurring 

 between the surface of the earth A and a reflecting horizon B. The mirror 

 image of A, with respect to B, is the plane A'. In this figure, O represents 

 the origin or shot-point, located on the surface of the earth. Using the 

 theory of images, we can locate the image of 0, which will be O' with 

 respect to the reflecting horizon B. 0" is the image of O with respect to 



t An excellent symposium on n^ultiple reflections is given in Geophysics, Vol. XIII, No. 1, 

 January, 1948, with papers by T. P. Ellsworth, C. H. Johnson, John Sloat, Frank Ittner, Joseph C. 

 Waterman, Beno Gutenberg, C. Y. Fu, C. H. Dix, O. C. Lester, Dean Walling, C. H. Dresbach, 

 and Raul F. Hansen. 



