THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS 
TRANS. SOCIETY PETROLEUM GEOPHYSICISTS, VOL. V (MARCH, 1935), PP. 154-160, 7 FIGS. 
STUDY OF EMERGENCE ANGLE AND PROPAGATION 
PATHS OF SEISMIC WAVES! 
MAURICE EWING anp A. P. CRARY? 
Bethlehem, Pennsylvania 
SUMMARY 
Travel-time curves are given for elastic waves through the earth in a regionin 
which the velocity increases continuously with depth. These time-distance curves have 
been approximated by an equation of the form X =a7?-+-bT from which the velocity 
depth relation has been deduced. A new method for measurement of the emergence 
angle has been used and the values obtained agree reasonably well with those deduced 
from theoretical treatment of the time-distance curve. Formulas for the travel-time 
between any two points in the medium under consideration are derived. These formulas 
agree closely with two sets of direct measurements. In one of these the seismograph was 
placed at various distances directly beneath the explosion. In the second case it was 
placed at a fixed depth beneath the surface and the explosion was located on the surface 
at various distances. The approximate depth to bed rock is obtained from the time- 
distance curves by use of the formulas mentioned above. 
The theory of the propagation of elastic waves through the earth 
in a region in which the velocity increases with depth in such a fashion 
that the observed time-distance curve may be represented by the 
equation 
X = aT*+ b6T (1) 
has been treated by Ewing and Leet.? The present paper includes an 
extension of the theory and an experimental investigation of many 
points in connection therewith. The data used were taken near Green 
Pond, Northampton County, Pennsylvania. The material at the sur- 
face was a fine grained alluvial deposit, which was underlain by lime- 
stone. The surface of the limestone was probably quite irregular. 
TIME-DISTANCE DATA AND VELOCITY-DEPTH DETERMINATION 
The time-distance data are shown in Figure 1. The curved lines 
drawn represent Eq. (1) with 
a = 29,600 ft./sec.?, b = 752.9 ft./sec. 
1 Reprinted from Physics, Vol. 5, No. 10 (October, 1934), pp. 317-20, with the 
permission of the editor of The American Physical Society and the authors. Manuscript 
received by Physics, May 24, 1934. 
2 Lehigh University. 
814 154 
