24 



METHODS OF GEOPHYSICAL EXPLORATION 



[Chap. 2 



the surface. If squares of travel times are plotted against squares of 

 distances, the square of the average velocity follows from the slope of 



Heiland Research Corp. 



Fig. 2-lL Wave paths, record, and arrangement of seismic reflection party. 



such curve. Because of the delay affecting primarily the return ray in 

 the low-velocity surface zone, a "weathered layer" correction must be 

 apphed. Data for this correction are obtained by the refraction procedure 



