644 EXPLORATION GEOPHYSICS 



the corresponding amplitude of the earth's motion. In some installations, 

 where electrical amplification is employed, the magnification may be as 

 great as 100,000 times. 



Fig. 400. — Vertical component variable reluctance electromag- 

 netic seismometer. A, inertia mass containing spring suspension; 

 B, transducer; C, adjusting nuts; D, leveling screw. (Courtesy of 

 Hugo Benioff, California Institute of Technology.) 



Figure 405 is a schematic representation of an earthquake record or 

 seismogram. Some of the more prominent waves or "phases," as they 

 are usually called, have been designated on the records by the letters P, 

 S, L, and M. The various types of waves, i.e., the various "phases," are 

 propagated with different velocities, depending upon their mode of vibra- 

 tion and the character of the medium through which they travel. 



In the primary or P waves, the vibrations of the earth particles are 



