CRUSTAL MOVEMENTS 197 



Frequency. Earthquakes are very common, though fortunately 

 those which are violent enough to be destructive are rare. From 

 1889 to 1899, an average of 36 per year were recorded in California 

 alone, but most of them were so slight as to do no damage. In 



Fig. 195. Deformed railway, Seventh and Mission Streets, San Francisco. 



Japan, earthquakes have been recorded at the rate of several a day 

 for many years, but many of them are very slight, and only a few 

 violent enough to be destructive. 



The Isthmus of Panama and its surroundings were under care- 

 ful observation with reference to earthquakes for a few years, 

 because the frequency and violence of earthquakes had a bearing 

 on the site which should be chosen for the canal which is to join 

 the Atlantic and Pacific. In 40 months, January, 1901, to April, 

 1904, 169 earthquakes were recorded at San Jose, near the eastern 

 end of the proposed Nicarauguan route. Of these, 43 were mere 

 tremors, 91 slight shocks, and 35 strong shocks. During the same 

 period, 6 tremors and 4 slight shocks were recorded at Panama, 

 near the site of the route along which the canal is being dug. 



In view of what is now known of earthquakes and earth tremors, 

 it has been said that some part of the earth's surface is probably 



