274 T. Tekada and T. Matuzaava 



from liis long experience, succeeded in sorting out a number of cha- 

 racteristic types of seisniograms obtained in Tokyo so that he can, 

 in the majority of cases, tell the X)rovenance at the first look at the 

 graph. 



Though the variety of the seismograph curves has been usually 

 attributed to the effect of the heterogeneity of the earth crust on 

 the way to the propagation of seismic waves, we have not yet reached 

 the point of analysing the complicated spectrum of waves into their 

 components with anything like indisputable accuracy. The difficulty 

 is of course connected with the reliability of the seismograph as the 

 faithful recorder of the actual motion of the earth. In this latter 

 connexion, 8aem Nakamura's*^^ attempt to analyse the seisniic motion 

 into a succession of distinct pulses may be mentioned. 



The existence of the long surface wave of the Rayleigh type has 

 been difficult to ascertain in many cases of near earthquakes. As 

 shown by Omori'-^, Imamura^"^, Kusakabe^''^ Hasegawa^^^, S. Nakamura^"^ 

 Suda^'^' and others^®\ the first conspicuous motion of the principal 

 portion of the waves is sometimes in the radial, but more frequently 

 in the transverse, direction relative to the origin. One of the most 

 remarkable examples is the case of the Simabara earthquake of 1922^^^ 

 in which the greatest motion was everywhere tangential to the circle 

 with its centre at the origin. On the other hand, it was pointed out 

 by Omori^^"^ that, in Tokyo, the first maximum motion is almost 

 invariably in a definite direction, E — W, f()r different earthquakes 

 with their centres at or near the Bay of Tokyo. In this respect, the 

 recent theoretical investigation by H. Nakano^"^ is of interest for it 



(1) N.S.B.K., [iii] 1 (1919), 88 ; Bull. C.M.O., 3, No. 2 (1920). 



(2) Among others, Ho., 54 (1906) ; Seism. N., 3 (1922). 



(3) Ho , 77 (1913). 



(4) T.S.B.K., 3 (1906), 10. 



(5) J.M.S., 33 (1914), 269. 



(6) J.M.S., 37 (1918), 390; 41 (1922), 139; 42 (1923), e. 1. 



(7) U.t.S., 3 (1923), 14. 



(8) Ohasi, Ho., 82 (1915). G. Isida. J.M.S., 34 (1915), 61. T. Sasaki, J.M.S., 35 

 (1916), 147. K. Taguti, U.t.S., 4 (1924), 199. T. Isikawa, Kensinziho, i (1925), 

 171 ; etc. 



(9) Omori, Ho., 99 (1925). Imamura, Ho., 99 (1925). S. Nakamura, J.M.S., 42 

 (1923), 1. Suda, U.t.S., 3 (1923) 2, 14. T. Ogawa, Mem. Kyo., Bl. No. 2 Art. 2 

 (1924). 



(10) Loo. cit. 



(11) Jap. J. Astr. Geophys., 2 (1925), 233. 



