NOTE ON THE THEORY OF SEISMIC PROSPECTING* 
Ce HDi 
Geophysics Department, Humble Oil and Refining Company 
INTRODUCTION 
As is well known, the field procedure in refraction prospecting 
consists of the establishment of shot points, i.e., sources of elastic dis- 
turbances, and seismic detector locations. The impulse is started ata 
shot point by setting off an explosive. The impulse energy spreads 
in all directions. These impulses travel along various paths to the 
detector locations. What is recorded is the time required for the im- 
pulse to travel from the:shot point to each detector location. 
The only character of wave transmission that is used is the trans- 
mission velocity. Fortunately for prospectors, the velocities usually 
increase with depth. Again fortunately the velocity of propagation 
in any given stratum usually does not vary very much as one moves 
over an area being surveyed. 
Although we do not consider anything below the bottom of the 
first stratum in this paper, still the general method adopted here can 
be profitably applied to deeper layers. 
The theory of refraction prospecting is well worked out for the 
case where the detectors are on lines through the shot point. According 
to this theory if one graphs the travel time as ordinate and the distance 
as abscissa for such a set of detector locations the graph is a polygonal 
line through the origin. Starting from the origin the graph is straight 
until at a certain critical distance we meet the first corner. Then the 
graph proceeds again until at another critical distance we meet an- 
other corner. At each corner the slope is diminished in numerical 
value. 
Imagine a single shot point S and, instead of locating detectors 
on just one line through S, locate detectors on all lines through S. 
For each direction through S there is a time-distance graph. Select 
any value of the travel-time, say J». Then for each direction through 
S there is a distant point, So, such that the travel-time from S to So 
is To. If we hold S and 7) constant and vary the direction of the line 
through SS, So will trace a path on the surface of the earth which we 
* Published by permission of the Board of Directors of Humble Oil and Refining 
Company. 
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