90 EARTH FEATURES AND THEIR MEANING 



supports, the danger of overthrow and of tearing apart is increased. 

 In general, structures are best constructed of light materials whose 

 weight is concentrated near the ground. Masonry structures, 

 and especially high ones, are, therefore, the least suited for resisting 

 earthquakes, of which the late complete destruction of the city 

 of Messina is a grewsome reminder. Despite repeated warnings 

 in the past, the buildings of that stricken city were generally con- 

 structed of heavy rubble, which in addition had been poorly ce- 

 mented (Fig. 49, p. 67). Such structures are usually first ruptured 

 at the edges and corners, since here the vibrations which tend to 



FIG. 85. House wrecked in San Francisco earthquake of 1906 because the floors 

 and partitions were not securely fastened to the walls (after R. L. Humphrey) . 



tear the building asunder are resisted by no supports and are 

 reenforced from neighboring walls. 



An advantage of the first importance is evidently secured if the 

 rods of the pendulum, of which the building is conceived to be com- 

 posed, have sufficient elasticity to be considerably distorted with- 

 out rupture and to again recover their original position. This is 

 the supreme advantage of structural steel for all large buildings, 

 which is coupled, however, with the disadvantage that the 

 riveted fastenings are apt to be quickly sheered off under the 

 vibrations. Large and high buildings, when sufficiently elastic, 

 have fortunately the property of destroying the earth waves 

 by interference before they have traveled above the lower 

 stories. 



For large structures in which wood cannot be used, strongly 



