THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS 
TRANS. SOCIETY PETROLEUM GEOPHYSICISTS, VOL. V (MARCH, 1935), PP. 117-120, 1 FIG. 
A FORMULA FOR WEATHERING CORRECTION! 
H. M. RUTHERFORD? 
Pittsburgh, Pennsylvania 
It is a well known fact that practically everywhere the outer por- 
tion of the Earth’s crust is composed of weathered material. The 
thickness of this weathered zone may vary from zero to 50, or more, 
feet within short distances. The velocity of seismic waves in this ma- 
terial is not uniform but varies in a very marked manner from top to 
bottom, as is readily seen on the weathered-zone time-distance chart. 
As a consequence, it has been found necessary in seismic reflection- 
work to base all calculations from the bottom of the weathered zone. 
An average velocity can be used below the weathered zone, since the 
velocity becomes more uniform in this part of the section. 
It is common practice, however, to calibrate an average velocity 
for the weathered zone itself due, perhaps, to the fact that no better 
method has been presented. It is at once apparent, however, that 
such a calibrated weathered-zone velocity is not actually valid and 
may lead to serious errors in determining the amount of time to be 
subtracted for the weathered zone, as well as its thickness. It is the 
purpose of this paper to present a formula whereby the thickness of 
the weathered zone may be calculated, and thus the proper time-cor- 
rection applied. The usual method for the calculation of depths by the 
seismic reflection-method has been given by the author in a previous 
paper.® 
It is necessary, in order to calculate the thickness of the weathered 
zone, to know in what manner the velocity of propagation varies with 
the depth of penetration. A method for doing this was first presented 
by Ewing.‘ Ewing found that the penetration is given by the formula, 
P(D) = (fx) f [cosh-*V (D)/V (x) |dx. 
+ Reprinted from The National Research Council of The National Academy of 
Sciences, Trans. Amer. Geophysical Union (June, 1934), pp. 78-80, with the permission 
of the general secretary of The American Geophysical Union and the author. 
2 Seismograph Station, University of Pittsburgh. 
3H. M. Rutherford, ‘‘Reflection-Methods in Seismic Prospectiny,”’ Amer. Inst. 
Min. Eng., Tech. Pub. 486. 
4M. Ewing and L. D. Leet, ‘‘Comparison of Two Methods for Interpretation of 
Seismic Time-Distance Graphs Which Are Smooth Curves,”’ Trans. Amer. Inst. Min. 
Eng., Geophysical Prospecting, 1932, pp. 263-270. 
II 
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