EARTHQUAKES AND SEAQUAKES 89 



which is supported by the loose braid because of the large range 

 or amplitude of movement that is imparted to the pan. The 

 " elastic " braid, because of these large vibrations of which it is 

 susceptible, may represent the loose materials when an earthquake 

 wave passes into them. In the case of the steel support, the 

 energy of the blow, instead of being dissipated in local swingings 

 of the pan, is to a large extent transmitted through the elastic 

 metal to materials beyond. The steel thus resembles in its high 

 elasticity the firmer rock basement, which receives and transmits 

 the earthquake shocks, but except when ruptured in a fault is 

 subject to vibrations of small amplitude only. 



Construction in earthquake regions. Wherever earthquakes 

 have been felt, they are certain to occur again; and wherever 

 mountains are growing or changes of level are in progress, there 

 no record of past earthquakes is required in order to forecast the 

 future seismic history. Although the future earthquakes may be 

 predicted, the time of their coming is, fortunately or unfortunately, 

 still hidden from us. If one's lot is to be cast in an earthquake 

 country, the only sane course to pursue is to build with due regard 

 to future contingencies. 



The danger from destructive fires may to-day be largely met 

 by methods of construction which levy an additional burden of 

 cost. Though the danger from seismic disturbances can hardly 

 be met as fully as that from fire, yet it is true that buildings may 

 be so constructed as to withstand all save those heaviest shocks 

 in the immediate vicinity of the lines of large displacement. Here, 

 also, a considerable additional expense is involved in the method 

 of construction, in the case of residences particularly. 



From what has been said, it is obvious that much of the danger 

 from earthquakes can be met by a choice of site away from lines 

 of important fracture and from areas of relatively loose foundation. 

 The choice of building materials is next of importance. Those 

 buildings which succumb to earthquakes are in most cases racked 

 or shaken apart, and thus they become a prey to their own inherent 

 properties of inertia. Each part of a structure may be regarded 

 as a weight which is balanced upon a stiff rod and pivoted upon 

 the ground. When shocks arrive, each part tends to be thrown 

 into vibration after the manner of an inverted pendulum. In 

 proportion, therefore, as the weights are large and rest upon long 



