EARTHQUAKE AREAS OF THE EARTH 451 



astrous Lisbon earthquake was also in a non-volcanic area. Likewise, 

 the region of occurrence of the recent Italian earthquake shows that it 

 also is situated in a non-volcanic area. Furthermore, as a general rule 

 ■ — though earthquakes often happen in volcanic regions due to explosive 

 shocks — the most disastrous and most powerful earthquakes occur in 

 non-volcanic areas and are tectonic in their nature. They — the latter — 

 are due to a series of rapid shocks which accompany movements along 

 lines of weakness, such as faults or previously made fissures due to 

 mountain-making movements. The throw of these faults need not be 

 very great in order to produce disastrous results. 



The frequent coincidence in the distribution of earthquakes and 

 volcanoes may be said to be due to their dependence upon a common 

 cause, in the sense that volcanoes may be regarded as incidental to and 

 the result of great earth movements. Such movements evidence either 

 the collapse of large areas of the earth's crust, or crustal uplift — each a 

 warping, and both due to movements of an orogenic or mountain-making 

 character. These crustal crinklings, moreover, which occur on a vast 

 scale, are not confined to one period of the earth's history, but have been 

 experienced by the earth at different times since the very beginning 

 and are likely to continue to the end — which, considering the physics 

 of the earth, and various well-known geological facts, appears to be fully 

 as remote as the genesis of the earth itself. 



