140 F. GOLDSTONE 
completely eliminated by such means as a wave filter. Common prac- 
tice is to use from four to six seismometers spaced from 50 to 200 feet 
apart. Shot points are normally located at intervals of about half a 
mile, but this spacing is determined by the complexity of the structure 
problem and also by the quality of the records obtained. The dyna- 
mite charges range from less than a pound to over 50 pounds, about 
one pound of 60% gelatin dynamite being a normal charge. The dyna- 
mite is usually loaded in machine-dug holes 20 to 100 feet or more in 
depth, the depth being governed by experience in a particular area. 
METHODS OF INTERPRETATION 
The method of interpretation used in Oklahoma is that of “‘cor- 
relation,”’ which implies that the same events can be recognised on all 
seismograms and correlated one with another over considerable dis- 

600 fee! Sersmometer 
spread 
“\ Difference in depth available scofert Difference m depth svsilable? 
for measuremen for measurement 
Fic. 4.—‘‘Correlation”’ and “‘dip”’ methods of procedure. 
tances. In areas where limestone members are continuous and where 
correlation of well logs by lithology is possible this method of inter- 
pretation is also possible. In fact, we may look upon a reflexion seismo- 
gram as a derivative of the lithological log of the stratigraphical 
column being penetrated by the reflected waves. In areas where litho- 
logical correlation cannot be carried over complete structures the same 
limitations will pertain to the interpretation of reflexion shooting data. 
For such areas the technique of ‘‘dip”’ shooting has been developed. 
This involves the very accurate determination of the running time of 
events reflected from adjacent points on a reflecting surface. Figure 4 
will assist in visualising the differences of these methods, and to those 
familiar with core drilling the analogy between core-drill mapping 
where a recognisable marker is available and mapping by dips meas- 
ured on core samples gives a fair representation of the relative power 
of tne two methods of attack. 
MAPPING BY CORRELATION 
Experience has shown that where events on seismograms can be 
correlated with certainty, all other processes of the method can be 
800 
