APPLICATION OF SEISMOGRAPHY TO 
GEOLOGICAL PROBLEMS: 
EUGENE McDERMOTT? 
Dallas, Texas 
ABSTRACT 
This paper contains an outline of the principles and methods of applied seismog- 
raphy. The science of seismography is predicated on the elastic properties of earth 
materials. The refraction and reflection of elastic waves and the conditions governing 
these are considered. These two phenomena are closely related. The application of 
the seismic method to salt-dome exploration on the Gulf Coast and the development 
of the refraction method for general structure determination is followed by an expla- 
nation of the reflection method. Several actual reflection records indicate the method 
of identifying reflections. 
INTRODUCTION 
The purpose of the writer is to present to the geologist rather than 
the practicing geophysicist the theory and method of applied seismog- 
raphy. The science of seismography derives its value from the fact that 
earth materials are elastic and this elasticity has extensive variations. 
The term seismography as used herein applies to the science which util- 
izes elastic waves that are generated artificially, as by an explosive charge. 
GENERAL THEORY 
In general, all materials are elastic, but in varying degrees. By 
elasticity is meant the resistance a material offers to changing its volume 
or form when subjected to stress. When stressed a material yields. This 
yield or change in volume or form is known asa strain. Elasticity may 
now be defined more accurately as the ratio of this stress to the resulting 
strain. This strain is propagated through the material with a definite 
velocity which is a function only of the elasticity and density of the 
material. This wave of strain is propagated in all directions in a straight 
line if the material is homogeneous or, more accurately stated, the wave 
front is spherical. If the material is not homogeneous the path is curved, 
that is, the wave is gently refracted, and the wave front is no longer 
*Read before the Association at the San Antonio meeting, March 20, 1931. Man- 
uscript received, June 4, 1931. 
2Geophysical Service, Inc., 1311 Republic Bank Building. 
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