Periodicity of Earth quakes. 467 



Kurnamoto, 148 ; Gifu, 1258 ; Nagoya, 572 ; Chiran, 233 ; 

 Nemuro, 345. 



The Kurnamoto earthquake occurred on July 28, 1889 ; 

 the Mino-Owari earthquake on October 28, 1891 ; the Kago- 

 shima earthquake on September 7, 1893 ; and the Nemuro 

 earthquake on March 22, 1894. 





Kurnamoto. 



Gifu. 



Nag 



oya. 



Chiran. 



Nem 



Ul'O. 



Harmonic 

 Components. 



















Ampl. 



Epoch. 

 h m 



Ampl. 



Epoch. 

 h m 



A.M. 



2 19 



Ampl. 



Epoch, 

 h m 



Ampl. 



Epoch. 

 h m 



A.M. 



4 35 



Ampl. 



Epoch . 

 h m 



A.M. 



4 12 



1st (24 hours) . 



•623 



A.M. 



3 



•163 



•505 



A.M. 



15 



•096 



•204 



2nd (12 hours) . 



•456 



2 35 



•089 



5 29 



•171 



1 25 



•069 



3 58 



•200 



8 27 



3rd (8 hours)... 



•430 



2 57 



•229 



3 58 



•111 



1 17 



•075 



6 52 



•327 



5 53 



4th (6 hours)... 



•214 



1 56 



•069 



1 12 



•068 



1 41 



•086 



2 18 



•052 



4 42 



5th (4# hours) . 



•239 



1 12 



•051 



50 



072 



1 33 



•121 



40 



•148 



3 10 



6th (4 hours)... 



•088 



52 



•121 



32 



•210 



37 



•239 



1 57 



•293 



55 



The numerous slight shocks which follow a severe earth- 

 quake are subject at first to a rapid decline in frequency*. 

 Now, if a simple harmonic series be superposed on a declining- 

 linear series, the harmonic analysis of the compound series 

 shows that not only are the amplitude and epoch of the 

 function of the same period changed, but minor harmonic 

 components are also introduced. It is clear therefore that the 

 epochs given above cannot be supposed to agree exactly with 

 those of their physical equivalents. At the same time, the 

 omission of the first one, two, three, and four days in succes- 

 sion from the Gifu and Nagoya records produces no important 

 change in most of the components. Moreover, as will be seen 

 in the next section, the different conditions introduced by the 

 occurrence of a great earthquake endure even when the decline 

 in average frequency of the after- shocks ceases to be sensible. 



The results for Gifu and Nagoya confirm those obtained 

 by Prof. Omori by a different method of analysis, the 8-hour 

 component being more marked at Gifu, and the 4-hour com- 

 ponent at Nagoya. Prof. Omori gives the time of each shock 

 recorded at both places until the end of Nov. 10, those at 

 Nagoya to the nearest second, and those at Gifu generally to 

 the nearest minute. Out of 1257 shocks recorded at Gifu 



* F. Omori, Journal of the Coll. of Science, Imp. Univ. Japan, vol. vii, 

 1894, pp. 111-126 j Seismol. Joiirn. of Japan, vol. iii. 1894, pp. 71-60. 

 See also Natural Science, vol. vi. 1895, pp. 391-397. 



