ox THE AFTER-SHOCKS OF EARTHQUAKES. I47 



instability under the Echizen, Mino, Owari, uud j\Iika\va provinces, 

 and that the great earthquake Avas caused by some big fractures 

 produced in this underground strained portion of the earth's crust. 



The district adjoining the south-eastern extremity of the Neo- 

 Yalley is not yet on tlie way of steadily settling into equihbrium, and 

 the four axial lines in Fig. 27 proliably indicate the positions of f<nn- 

 weaker or deeper fractures, the peculiar violence of motion on the 

 occasion of the great earthquake in the zonal tract at the western part 

 of the Owari Tlain and in the regions to the south-east of Koori (see 

 Fig. 26) being probably due to the existence of such lines of weakness 

 beneatli.' The underground fracture along the Neo- Valley was pro- 

 bably sufficiently great and must have removed the chief centre of 

 weakness at that district. 



Tlie two axial lines in Fig. 2(S seem to indicate the positions of 

 fracture lines which Ijecame gradually |)rominent, and along which 

 the activity of after-shocks is at present greatest. 



The centre of activity of after-shocks may in future change its 

 position, l)ut it will very probably recede from, and not approach the 

 JN'eo- Valley. 



The distribution of seismic activity before 1<S!)1 is shewn iu Fig. 

 oO (see Table XXIT). It indicates no such [>eculiarity as that seen 

 in F'igs. 27, 28, and 29. 



§ 06. EarlJi inal^r Sonnls. — I take thi.» ()p[)nrtunity of making 

 S(jme remarks upon earth(|uake sounds. 



Many of the after-sliocks of the Mino-Owaii earth(piake were 

 attended with s(Hinds, which were essentially of two types, being 

 either rushing feeble noises like those caused by winds, or loud 

 rumbling S(.ninds like those caused by the fdling(jf a heavy weight on 

 y^round, or Ijy the dischar^'e of a u'un. 



1 See Fi"-. 31. 



