638 



WM. HERBERT HOBBS 



ments of bridges have approached each other during earthquakes,^ 

 and it is now proposed to assemble the evidence on which the state- 

 ment was based and to suggest an explanation of the phenomenon. 

 It is to the descriptions of destructive earthquakes of comparatively 

 recent date and in countries of considerable industrial development 

 that we must go for our evidence, since it is the bridges of better con- 

 struction, and the railroad bridges especially, which furnish the 

 most satisfactory evidence. Data are available from the Charles- 

 ton earthquake of 1886, the Japanese earthquakes of 1891 and 1894, 

 the Indian earthquake of 1897, the California earthquake of 1906, 

 the Kingston earthquake of 1907, and probably others. 



THE "CHARLESTON" EARTHQUAKE OF AUGUST 3I, 1886 



A typical illustration is here furnished by the Charleston and 

 Savannah Railway bridge over the Ashley River after the earthquake 

 of August 31, 1886.^ The diagrammatic sketch after Dutton, which is 

 reproduced here in Fig. 2, is especially valuable, since it well illustrates 



a characteristic distortion of 

 the abutments of bridges 

 observed after a destructive 

 earthquake. Of this bridge 

 Dutton says: 



The approach to the bridge 

 is by a long embankment, trav- 

 ersing a marshy flat v/ith an 

 ascending grade, giving place 

 near the bridge to a high trestle. An embankment and trestle lead to the bridge 

 from the opposite side. The draw-bridge was closely jammed by the earth- 

 quake, the immediate cause being the sliding or creeping of both river banks 

 toward the center of the stream, carrying the trestle with them. West of the 

 river the joints of the rails were torn open by tension produced in this sliding 

 motion. (P. 304.) 



The only other railroad bridge within the so-called "epicentral 

 tract" of this earthquake was on the same Hne of railway near Ran- 

 towles Station: 



I Earthquakes, An Introduction to Seismic Geology (D. Appleton & Co.), 1907, 

 p. 230. 



3 C. E. Dutton, "The Charleston Earthquake," gth Annual Report, U. S. Geol. 

 Survey, p. 231. 



Fig. 2. — Bridge over the Ashley River, South 

 Carolina, as it appeared after the earthquake of 

 August 31, 1886 (after Dutton). 



