122 



F. OMORI. 



the initial earthquake hefore the number of shocks in the disturbed tract 

 about Kumamoto can attain its original yearly average, if at all. 



§ 14:. We have seen (§ 7) that the number of after-shocks of 

 the Mino-Owari earthquake during the first two years is about four 

 times greater thfin that of the Kumamoto earthquake during the 

 corresponding interval of time. If we now assume that the seismic 

 frequency at Gifu after a given interval of time from the Mino-Owari 

 earthquake is always greater by this ratio than that at Kumamoto after 

 an equal interval from the Kumamoto earthquake, the result inferred 

 from the analogy of the latter is that some nine or ten years will 

 elapse before the yearly number of earthquakes at Gifu is reduced to 

 ten or twelve (compare § 1 1). 



The great earthquake of üctol)er 28th, 1891, must have removed 

 the principal geotechtonic instability which had existed beneath 

 the Mino-Owari district, and in this part of tlie country the present 

 epoch of seismic activity will be followed ])robal)Iy Ijy one of rest. 

 The average yearly number of earth(|uakes at Gifu before 181)1 was 

 about 15. 



§ 15. I shall here remark that the space distrilmtion of seismic 

 energy as represented by the relative number of earthquakes during a 

 given interval of time may vary from time to time, and particularly 

 with the occurrence of great earthquakes. In general there is a coin- 

 cidence between the distri1)ution of destructive shocks and that of 

 ordinary minor ones, and the latter may be the consequences of the 

 former. In Japan the seismic activity, as far as smtdl enrth(|uakes 

 are concerned, is much greater on the Pacific than on the Ja])an Sea 

 side, and so is it with destructive shocks, of which 57 ^'/o took 

 place on the Pacific side, 28 »/o on the Japan Sea side, and only 

 the remaining 15 ^/o remote from either. More especially the 

 great shock of the 1st year of Ansei (1854), which affected severely 



