96 EARTHQUAKES. 



CHAPTER VI. 



EFFECTS PRODUCED BY EARTHQUAKES UPON BUILDINGS. 



The destruction of buildings is not irregular — Cracks in buildings — 

 Buildings in Tokio — Relation of destruction to earthquake motion — 

 Measurement of relative motion of parts of a building shaken by an 

 earthquake — Prevention of cracks — Direction of cracks — The pitch 

 of roofs — Relative position of openings in a wall — The last house 

 in a row — The swing of buildings — Principle of relative vibrational 

 periods. 



The subject of this chapter is, from a practical point of 

 view, one of the most important with which a seismologist 

 has to deal. We cannot prevent the occurrence of earth- 

 quakes, and unless we avoid earthquake-shaken regions, 

 we have not the means of escaping from them. What we 

 can do, however, is in some degree to protect ourselves. 

 By studying the effects produced by earthquakes upon 

 buildings of different construction and variously situated, 

 we are taught how to avoid or at least to mitigate calamities 

 which, in certain regions of the world, are continually 

 repeated. The subject is an extensive one, and what is 

 here said about it must be regarded only as a contribution 

 to the work of future writers who may give it the atten- 

 tion it deservedly requires. 



The Destruction produced by Earthquakes is not 

 irregular. — If we were suddenly placed amongst the 

 ruins of a large city which had been shattered by an 

 earthquake, it is doubtful whether we should at once 



