DE VEL OP ME NT OF SElSMOL OGY IN J A PAN 263 



the recent Kwanto earthquake respectively. On the other hand, the 

 characteristic deviation from the algehraic formuhi was studied by 

 T. Terada^^Hvho showed that the apparent periodic fluctuation may 

 result from purely accidental causes, but that the ajiparent period 

 may give some clue for studying the elastic property of the earth 

 crust. 



Saem. Nakamuva^-^ remarked a jieviodicity of 1"^ 40^ in the case 

 of the Hakone earthquake of 1907. R. Hirano'''^ made an interesting 

 investigation with respect to the after-shocks of the recent Kwanto 

 earthquake. He assumed an empirical formula y=:h/{x + ay where 

 y is the number of after-shocks on the xA\\ day, and a, b, c are 

 constants. It is remarked that the values of the constants change 

 abruptly at 07=19. Besides, he observed a maiked periodicity of 19.2 

 days in the 10 days mean of log?/, which he tries to explain 

 by the alternating excitation of a number of discrete sources of 

 activity. 



K. Suda^^^ classified the after-shocks of the Kwanto Earthquake 

 into two families according to the position of the origins. Some 

 characteristic behaviour of these families as well as the mode of 

 migration of activity among them are discussed. He also noticed a 

 marked discontinuity in the hyperbolic course of decay. 



Imamura^^^ also made a careful examination on the distribution 

 of the origin of after-shocks of the same earthquake and obtained 

 three distinct groups of the localities of the origins. The different 

 groups behaved differently in the time distribution of the frequency. 



A similar study by K. Shiratori^^* may also be mentioned who 

 arrived at an N-shaped zone of the origin of the after-shocks. 



(h) Relation of the frequency of earthquakes with meteorological 

 and other phenomena. As already cited, Omori*^'^ discussed the effects 

 of barometric pressure with regard to the annual and diurnal varia- 

 tions of the earthquake frequency. In the meanwhile, he^*^ studied 



(1) N.S.B.K., [iii] 1 (1919), 180. 



(2) Journ. Met. Soc, 36 (1917), 67, e. 

 (3j Journ. Met. Soc, 43 (1924), 77. 



(4) Mem. Imp. Mar. Obs., 1, No. 4 (1924i. 



(5) Ho., lOOA (1925j; Seism. N, 6 (1924). C. Yasuda, Ho., lOOA (1925). 

 (6j Jap. J. Astr. Geophys,, 2 (1925), 173. 



(7) loc. cit; also Bull. 2, No. 3 (1908); T.S.B.K., 2 (1904), 113. 



(8) Ho., 68A (1910); Bull., 1, No. 2 (1907); 2, No. 1 and 2 (1908); 5, No. 2 

 (1913). 



