276 T. Teeada and T. Matuzawa 



anomalies could also Le accounted for by assuming different kinds of 

 multiplet sources. K. Suda^''^ also discussed the cause of the anomaly 

 and laid stress on the effects of the mechanism of the origin. 



The fact that the geographical distribution of the intensity of 

 earthquakes shows a very conspicuous anomaly, has long since drawn 

 the attention of seismologists''-^ in this country. One of the most 

 conspicuous cases is that of the earthquake which originated on or off 

 the Pacific coast. In most of these earthquakes we may observe a 

 characteristic elongation or bulging out of the isoseismal curves along 

 the Pacific coast, as if the coastal districts were specially senaitive to 

 the seismic waves from these quarters. Again examples have been 

 cited by Shida^"'^ and Hasegawa^"" in which earthquakes which originated 

 in the Japan Sea were felt only on the Pacific coast, while the Japan 

 Sea coast immediately facing the origin suffered no perceptible shocks. 

 Terada^^^ tried to explain this anomaly by the special block structure 

 of the Pacific coast as revealed by the investigations of Yamasaki and 

 Tokuda already cited. In this connexion, S. Ono's'^^^ studies on the 

 isostatic blocks may be referred to. He points out the existence of 

 long waves with a period of 26 to 27 sec. which may possibly be 

 connected with the proper period of the block, the horizontal dimen- 

 sion of which he estimated at 60 km. 



The problem of the anomaly of isoseismals is also closely connected 

 with that of the dissipation of wave energy on the way of its pro- 

 pagation. In this respect, the investigations of Kusakabe*^^-, Saem. 

 Nakamura-'"^ and Suda*^"-, may be mentioned. Kusakabe based his 

 consideration on the results of his extensive experiments on the elastic 

 properties, especially on the hysteresis and after-effects, of different 

 specimens of rocks, and borrowing an analogy from the problems of 

 inagnetic induction and of heat conduction, introduced the idea of 



(1) K. Suda, U.t.S., 6 (1926), 24, et seq. 



(2) Omori, Ho., 3 (1895); 29 (1899); 34 (1901). Yamasaki, Ho., II (1897). 

 Tmamura, Ho., 53 (1906); 70 (1910); 77 (1913); 82 (1915). Y. Kikuti, Ho., 35 (1901). 

 N. Fukuchi, Ho., 38 (1901) ; H. Hatiya, Ho., S3 (1906). 



(3) Communicated to a Meeting of the E.I.C. ; not published. 



(4) J.M.S., 37 (1918), 202. 



(5) Geogr. Rev., 1 (1925), 841. 



(6) Kensinziho, I (1925), No. 2. 



(7) T.S.B.K., 3 (1906), 88; Bull. C.M.O., 3, No. 2 (1920). 



(8) J.M.S., 37 (1918), e. 43; 38 (1919), 147; NS.B.K., [iii] 1 (1919), 142. 



(9) J.M.S., 41 (1922), 426; Mem. Imp. Mar. Obs„ 1 (1923), 52. 



