MOVEMENTS AND DEFORMATIONS 



343 



of origin are the most irregular, and the stronger vibrations gener- 

 ally have greater speed than the weaker ones. The vibrations 



The two epwentral 

 isoseismal curves; the heavy line being the index. 

 SCALE OF MILES 



BORUAY ENS. CO., 



Fig. 277. Epicentral tracts of the Charleston earthquake, with isoseismal 

 lines. (Button, U. S. Geol. Surv.) 



propagated to great distances through and around the earth are 

 more uniform in rate, being about 1.85 miles (3 km.) per second 

 for those which follow the surface, about 5.7 miles (9.17 km.) 

 per second for the speedier set that goes through the earth, and 



