DEVELOPMENT OE SEISMOLOGY LV JAPAN 26/ 



of statistics improved, before anything positive may be said about 

 this matter. 



The relation of the seismic zones with the geological structure 

 of the land has been investigated from the earliest dates, by the 

 geologist members of the E.I.C/'\ On the occasion of the recent 

 Kwanto Earthquakes, many important contributions on this line have 

 been made by the geologists, T. Kato*'^^ N. Yamasaki^^^, T. Ogawa^"^', 

 and H. Yabe^^^ among others. Structural lines in the district in 

 question have been identified and their distributions discussed by 

 Ogawa, who has also studied the case of the Simabara earthquake of 

 1922, and confirmed his view that the orotectonic and the seismotect- 

 onic lines coincide with each other. 



Yamasaki made an extensive study on the block structure of the 

 Kwanto districts and drew attention to the extension of the same 

 structure into the bed of the Bay of Sagami, where the origin of 

 disturbance of the recent catastrophe is to be sought. Yabe gave a 

 very concise representation, of the geological structure of the Kwanto 

 Plain as an individual geological unit. These investigations have 

 thrown much light on the nature of the seismic zones. 



Kecently S. Ono^*'^ made an original study on the block structure 

 of land from the physical point of view and suggests the existence of 

 definite mean dimensions of these blocks which he estimate at about 

 60 km. in the horizontal extension. K. Sezawa^''^ also made an applica- 

 tion of the theory of elasticity on the block formation of the earth 

 crust and offered many interesting suggestions as to the origin and 

 nature of earthquake phenomena. 



It seems after all that we have now arrived at an epoch when 

 the vague conception of the seismic zone needs a thorough revision 

 and its exact physical meaning scrutinized much more thoroughly 

 than in former days. 



(1) to be cited later. 



(2) Journ. Geol. Soc, 30 (1924>, engl. p. 17; Ho., lOOB (1925). 



(3; Ho., lOOB (1925) ; Geogr. Eev., 1 (1925), 1 ; Journ. Fac Sci. Tok., 1 (1925), 35. 



(4) Chikyu, I (1924), 1, 113, 199 and 287; Mem. Coll. Sci. Kyo., B. I, No. 2, 

 Art. 4 (1924); Jap. J. Geogr., 3 (1924), 1. 



(5) Saito Hoonkwai Zigyo Nenipo, No. I (1925). 



(6) Kensin Ziho, 1 (1925), 1, 11. 



(7) Read before the Engineering Society of Tokyo Imp. Univ., also in the 

 Seismological Colloquium of the Seism. Inst. ; not yet published. 



