i8g 5 . THE AFTER-SHOCKS OF EARTHQUAKES. 397 



for January, 1894. In Fig. 2 the curves on the map for 1892 are 

 reproduced as dotted lines. 



It will be obvious from a glance at these curves that the after- 

 shocks were most frequent, not in the Neo Valley, where the great 

 fault-scarp was formed, but in a district to the south-east of it, in the 

 Mino-Owari plain. For some time after the great earthquake the 

 most active centre of after-shocks was situated close to Gifu, probably 

 just to the west of the town. During 1892, as is shown in Fig. 2, 

 there were four axial lines (A-D) radiating from the neighbourhood of 

 Koori, along which after-shocks were more numerous than in other 

 parts of the district. 



In succeeding years the distribution of seismic activity underwent 

 some changes. The curves of equal frequency during 1893 show a 

 diminution along the axial line marked A, while the prominence of 

 shocks along the axial line B almost entirely disappears. The other 

 two lines, however, remain still distinct, and, during January, 1894, 

 are the only representatives of the original number. This is due to 

 the fact that, on the 10th of this month, a severe earthquake occurred, 

 whose origin was situated at the point where these two axial lines 

 intersect. Two other severe earthquakes on January 3 and Sep- 

 tember 7, 1892, also originated in the Mino-Owari plain, one close to 

 Gifu and the other near Katsukawa. All three, therefore, had their 

 centres close to the axial line A C running W.N.W. and E.S.E. 



The interpretation of these facts seems to be, as Mr. Omori 

 suggests, that a prominent fracture or series of fractures exists 

 beneath the Neo Valley, and that by the great earthquake the stress 

 in this district was almost completely removed. The axial lines 

 radiating from Koori probably indicate the existence of four slighter or 

 deeper fractures, along which the crust is still gradually settling down 

 into equilibrium, that condition not being yet attained. The centre 

 of after-shocks, Mr. Omori concludes, may still further change its 

 position ; but he considers it more probable that it will recede from, 

 rather than approach, the Neo Valley. 



REFERENCES. 



1. Koto, B. — "The Cause of the great Earthquake in Central Japan, 1891." 



Joum. Coll. Sci. Imp. Univ. Japan, vol. v., pt. iv., 1893, pp. 295-353. 



2. Milne, J. — "A Note on the great Earthquake of October 28, 1891." 



Seismological Joum. Japan, vol. i., 1893, pp. 127-151. Brit. Assoc. Rep., 1892, 

 pp. 1 14-129. 



3. Omori, F. — " On After-shocks." Seismological Joum. Japan, vol. hi., 1894. 



pp. 71-80. 



4. -. — " On the After-shocks of Earthquakes." Joum. Coll. Sci. Imp. 



Univ. Japan, vol. vii., pt. ii., 1894, PP- n 1-200. 



Charles Davison. 

 King Edward's High School, Birmingham. 



