646 



EXPLORATION GEOPHYSICS 



Fig. 403. — Vertical component moving conductor seismometer. Cover removed show- 

 ing springs and inertia reactor. A, inertia mass; B, spring suspension; C, magnet; D, 

 arm carrying conductor; E, leveling screw. (Courtesy of Hugo Benioff, California Insti- 

 tute of Technology.) 



longitudinal, i.e., in the direction of propagation. In the secondary, or 

 6" waves, the vibrations are at right angles to the direction of propaga- 

 tion, and are termed transverse 

 waves. Although the P and 6" 

 waves traverse the same path, 

 they arrive at a seismological 

 station at different times, be- 

 cause the velocity of the longi- 

 tudinal (P) wave is greater 

 than that of the transverse (6") 

 wave. The complex "surface" 

 or L waves travel at a still 

 slower speed; hence, in gen- 

 eral, they arrive later than the 

 P and 5" waves. 



The earth is continually 

 undergoing slight vibration as 



Fig. 404.— Principle of variable reluctance seismom- is SCCn in the extreme left-hand 

 eter. A, armature carrying coils; B, pole pieces of ^. ^ -r^. /ir»e '-ni 



magnet; M, permanent magnet; C and C, coils. (Court- portlOn Ot i:^ Igure 4U5. 1 he 



esy of Hugo Benioff, California Institute of Tech- c^r^i- ^U^...^ A', .,^^^^^,^^■^^- ^( 



noiogy.) nrst sharp displacement oi 



