DE VEL OP ME NT OF SETS MO L OG Y IN JAPAN 273 



Wadati's recent investigation above cited has furnislied us with 

 another kind of nodal line, if we may call it so, which will serve as 

 an excellent means for studying the structure of the crust. 



Theoretical investigations connected with the above subject by 

 Nakano and Matu/awa will be referred to later in tlie proper place. 



(d) Nature of earthquake motion; anomaly of propagation, 

 Omori^'^ and Iraamura's"^^^ works regardiiig the analysis of seismograms 

 are classical and cover a wide domain including the most important 

 problems of seismology. The discrimination of different phases of 

 motion, the determination of the direction of motion and the average 

 period of each phase, the investigation of the relation between the 

 duration, the period, the amplitude, or the character of wave and the 

 epicentral distance, etc., have been exhaustively pursued, with regard 

 to local as well as world-shaking earthquakes'^"^ The results of 

 these works, we may presume, are too familiar to most of the readers 

 of this note to require to be enumerated here at considerable length. 



The analysis of seismograms into a series of distinct typical 

 phases corresponding to definite physical existences is however not 

 always an easy matter, especially in the case of near earthquakes. 

 Even at the present day, there seems to exist ample room for 

 different schools of seismology so that it is no w^onder if the European 

 methods were not })romptly adopted by our earlier seismologists. 



Omori^'^^ early remarked that there were many distinct types of 

 seismogTams, according to the different combinations of the origins 

 and the stations of observations. H. Maruoka^''^ also gave some 

 examples of such types in the cases of distant earthquakes. Imamura^*'^ 



(1) Ho., 29 (1899); 32 (1900); 41 (1903); 50 (1905'; 54 (1906); 68A (1910); 73 (1911); 

 79(1915); 99 (1925); Pub., 4 (1900); 5 (1901); 6 (1906); 10 (1902); 11 (1902,!; 13 (1903); 

 18 (1904); 21 (1905); 23 (1907); 24 (1907); Bull.. 1. No. 1, 2 3 and 4 (1907); 2, No. 



1 aud 2 (1908); Seism. N., 2 and 3 (1922); T.S.B.K., 1 (1903), 148, 221 ; 2 (1904), 193; 



2 (1905), 325, 458. 



(2) Ho., 35(1901); 77 (1913); 82 (1915); 99 (1925); lOOA (1925); Pub., 16 

 (1904). 



(3) For the data of distant earthquakes, see also : H. Maruoka, J.M.S., 26 

 (1907); 27 (1908) 151; 30 (1911), 79, 239; 31 (1912), 285; 33 (1914), 339. F. Nakano, 

 J.M.S., 26 (1907), 185. K. Hirata, J.M.S., 28 (1909), 111. K. Sibano, J.M.S., 31 (1912), 

 61. K. Hasegawa, J.M.S., 32 (1913) e. 27. 



(4) Pub., 21 (1905); T.S.B.K., 2 (1905), 193. 



(5) J.M.S., 41 (1922), 481. 



(6) Not vet published. 



