EARTHQUAKE MEASUREMENT AT MIYAKO. 187 



the commenceinent, the average period being 0.089 second in 

 the (EW), 0.081 second in the (NS), and 0.076 second in the 



(V). 



Summary of Results. 



The results are collected in the Table at tlie end of this 

 paper, to which the following remarks may be prefixed. 



36. The area of earthquahe disturbance. 



Of the earthquakes whose exact dates are known, No. 4 

 and its fore-and after-shocks, namely, Nos. 3, ö, 6, 8, and 19, 

 originated in the mountain regions forming the boundary between 

 the provinces of Rikuchu and Ugo, while the remaining 19 

 earthquakes all originated under the Pacific Ocean at variable 

 distances from the coast. The isoseismal lines and the areas of 

 disturbance of these earthquakes, the typical ones of which are 

 illustrated in figs. 4, o, 6, 7 and 8, were generally not circular, 

 but more or less elliptical, with the longer axes parallel to the 

 coast, that is to say, in a direction of N slightly E to S slightly 

 W. In the last column of the Table, therefore, both the great- 

 est and the least radii of propagation are given for each earth 

 quake, the exceptions being Nos. 22, 26, 4, 5, 6 and 10, whose 

 areas of disturbance were nearly circular. The smallest and the 

 greatest among the 25 earthquakes here considered, were respec- 

 tively No. 24 and No. 9, the radii of propagation of the former 

 being 50 and 65 km. and those of the latter 430 and 700 km. 



In those cases in which the earthquakes originated under 

 the Pacific Ocean, the shocks were generally propagated only 

 to an insignificant amount to the western coast of Japan. 

 This is probably due to the seismic weaves having been stopped 

 by the heavy mountain masses running through the Main Island. 



