AFTER-SHOCKS AND SPACE-DISTRTBUÏION OF SEISÄFIC WAVES. 



Thus the nmount of recovery increased, in the course of 

 about four davs, to more than twice its initial value. 



Frequency of After-Shocks. 



From what has been explained in the above section we know, 

 as a matter of fact, that a piece of rock yields under the constant 

 action of stress, and also that the residual strain surviving the 

 stress diminishes from instant to instant. This last phenomenon 

 must be the prime cause of the after-shocks. Thus, the first step 

 is to find some formula expressing the rate of recovery, or the 

 rate with which the residual varies with time. One form of such 



