ASYMMETRY OF SOUND VELOCITY 
IN STRATIFIED FORMATIONS 
By Burton McCouuvum anp F. A. SNELL 
McCo.ium ExpLoraTIon Company, Houston, TExas 
(Received February 23, 1932) 
ABSTRACT 
In the course of explorations of subsurface geology by the seismograph the authors 
have frequently observed the pronounced effect of stratification on the velocity of 
seismic waves in shales, and this effect has often been utilized in practical seismogra- 
phy. Recently an opportunity was afforded for securing additional quantitative data 
on the velocity normal to and parallel to the bedding planes. The paper points out 
that the velocity parallel to the planes of stratification is, in some instances, as much 
as fifty percent higher than the velocity in a direcvion normal to the bedding planes. 
It is shown also that inclined stratified beds exhibit a higher apparent point-to-point 
velocity when sound travels in an up-dip direction than when traveling down-dip. The 
paper describes a procedure whereby this effect may be utilized for determining the 
direction and approximate magnitude of the dip in such stratified deposits. The 
method has proved to be of considerable practical importance where the stratified 
formations are obscured by overlying deposits. 
GENERAL OUTLINE 
NE of the earliest applications of the seismograph was its use in profiling 
salt domes, limestone horizons, or other high velocity rock formations 
buried beneath sands, clays, or shales of lower velocity. In this method of 
profiling, the portion of the sound wave utilized travels substantially along 
the path shown diagrammatically in Fig. 1. As is well understood, the time 
interval between the arrival of the wave at two stations some distance apart 
Detectors 






ye 
High Velocity Rock + 
= -_ 
gh 2 tee oe - + 
v2 8 Nos er Coat Fa re 
es 
Fig. 1. Characteristic geology for diffraction profiling. 
along the line of propagation of the wave will be dependent on whether the 
wave is being propagated upslope or downslope. By measuring this velocity 
asymmetry the direction and magnitude of the slope of the high velocity bed 
can be determined. 
Commonly spoken of as diffraction or refraction shooting, this method 
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