392 



THE NATIONAL GEOGRAPHIC MAGAZINE 



VIEW ALONG QUAY IN MUSSINA SHOWING A DISPLACEMENT CAUSED BY LOCAL 



LAND-SLIPPING 



of one and two stories were much less 

 damaged than those of three and four 

 stories, and that many houses were trav- 

 ersed by cracks running north and south. 



To determine the character cf the con- 

 struction to be employed, the engineers 

 have the reports on the San Francisco, the 

 Japanese, and other earthquakes, which 

 discuss fully the effect of an earthquake 

 on all the varied types of structure. 

 With these and their present knowledge 

 of the structures in Messina there is 

 every reason to believe that they will de- 

 cide upon an individual type especially 

 adapted to this region that will give great 

 resistance to earthquake shocks. To the 

 government will fall the duty of enforc- 

 ing the use of this type of structure. 

 With buildings properly constructed the 

 destruction by earthquakes to life and 

 property will be minimized, so that cities 

 and towns along the straits will be much 

 safer to live in. 



WHAT EARTHQUAKES ARE 



Earthquakes are tremors or shakings 

 of the ground naturally produced. They 

 are superficial phenomena resulting from 

 a subterranean shock which is trans- 

 mitted as an elastic wave through the 

 material of the earth's crust. From 

 points of initial disturbance these waves 

 pass out in all directions. They are 

 caused by volcanic explosions and ac- 

 company the development of mountain 

 structure. With the contraction of the 

 earth's crust and adjustment of land' 

 masses powerful strains, consisting of 

 terrestrial pressure or tension, are de- 

 veloped, and wherever and whenever such 

 strains suffice to overcome the elasticity 

 of the rocks involved, either viscous flex- 

 ure or rupture must result. A disloca- 

 tion or tectonic earthquake, therefore, is 

 simply the jolt or jar produced by a sud- 

 den movement of the crust along a fault 



