EARTHQUAKE MOTION TO GREAT DISTATOBt 



ir, , 



Having thus two forms of wave motion projMigatud throng!) the earth, it is natural 

 to regard them as condensational and distortioiial, and this inference is strengthened 

 if we complete the curves and carry them on to the origin. They then give initial 

 velocities of transmission of about 5 and 3 kiloms. }>or second respectively. 



Little is known of the rate of transmission of elastic waves through rock. Direct 

 experimental determinations, hy measuring the rate of transmission of the disturb- 

 ance set up hy an explosion, give little assistance, as the velocities obtained are much 

 less than should result from the elastic constants of the rock, a difference probably 

 due to the weathered and fissured condition of all rocks near the surface. The only 

 experiments of much value are those of Professor GRAY and MILNK,* who measured 

 the elastic constants of certain rocks, and obtained results from which the following 

 rates of transmission of condensational and distortional waves were deduced : 



The original records of the experiments have been lost, and some doubts attach to 

 the absolute correctness of the results.t but they are prolsibly not seriously in error. 



In Professor KNOTT'S paperj the same experiments are referred to, but the elastic 

 constants differ slightly from those published in the ' Quarterly Journal.' Combining 

 them with the densities as given by Professor MILNE we get 



From the above we may conclude that the rates of transmission of elastic waves 

 through continuous rock such as is met with at a little distance from the surface, 



* ' Quart. Jour. Geol. Soc.,' vol. 39, 1883, p. 140. 



t 'Seismol. Jour.,' Japan, vol. 3, 1894, p. 87. 



J 'Trans. Seismol. Soc.,' Japan, vol. 12, 1888, p. 118. 



