AFTER-SHOCKS AND SPACE- DISTRIBUTION OF SEISMIC WAVES. 13 



centre of them will he transferred elsewhere to some neighbourlmj 

 weaker region. 



To give an example, in the case of the Miiio-Owari earth- 

 (jiiake,'^ wliieh was caused by a sudden falling of the Palaeozoic 

 strata on the right wing along the line of the ' fault of Neo,' 

 accompanied 1)V lateral shifting toward the north-west,'^ the 

 centre of the after-shocks was transferred considerably southward''^ 

 to the lowland of Mino and Owari, which is believed to have 

 been recently formed out of the sediments of the confluent streams, 

 the Kiso îind the Nagara.'*^ 



Iso-Frequency Curves of After-Shocks. 



The discussion in the last section refers to the frequency of 

 after-shocks in the very centre of the disturbance. Here a hint 

 is given to show how the geological distribution of rocks plays 

 the greater part in diversifying the foim of iso- frequency curves, 

 which would all be similar to each other if the earth w^ere a 

 homogeneous isotropic body. 



It is a matter of course that a seismic wave })ropagating 

 through a medium having a greater hysteresis fades more rapidly 

 than one propagating thi'ough another medium having a less 

 hysteresis. That is to say, the distance li)etween two successive 

 iso-frequency curves should be dependent on the geological dis- 

 tribution of the rocks in the region. Not only is the frequency 



1) A Mhort descriiition is fjiveii in Professors B. Koto's ami F. Oniori's papers eited 

 below. 



2) JÎ. Koto. On tlie canse of tiic Great Eartliquake in Central Japan, 18'J1. This 

 jonrnal, Vol. V. p. '.\öo. 



'.'>) F. Oinori. On the .\fter-shucks of Eartliqnakes. Tills journal, Vol. VII. 

 4) B. Koto. L'ic. ciied. p. o07. 



