340 



GEOLOGY 



rude first approximation to the location of the focus (point, line, 

 or plane), and all estimates made in this way are subject to im- 

 portant corrections. 1 



26 25 24 23 



21 20 19 18 17 10 



14 13 12 11 



Fig. 273. Seismograph of earthquake in Punjab, India, April 4, 1905, show- 

 ing the actual amount of movement. (Montessus de Ballore.) 



The amplitude of the vibrations. From the disastrous effects 

 of earthquakes it might be inferred that the vibrations have large 

 amplitudes; but it is chiefly their suddenness that makes them 



Fig. 274. A fissure on East Street, San Francisco, near the water front, 

 in "made ground." (Lindgren, U. S. Geol. Surv.) 



1 These corrections are due to the decrease in the elasticity, temperature, 

 density, and continuity of the rock as the surface is approached. See the 

 authors' larger work, Vol. I, p. 528 et seq. 



