EARTHQUAKE MEASUREMENT AT MIYAKO. 167 



The principal portion, whose duration was 4 seconds, con- 

 sisted essentially of three large well-defined vibrations of aii 

 average period of 1.0 second, the maximum horizontal motion 

 (period 0.94 second), being composed of the following two 

 displacements : 



(First motion) : 2a = 9.0 mm., direction S 79° W. 

 (Second motion) : 2« = 9.0 mm., direction N 79° E. 



The succeeding vibrations were executed also in nearly the 

 same direction, that is, ENE — WSW, the direction of motion, 

 however, gradually changing as w-e pass into later and smaller 

 vibrations. Thus the second vibration after the maximum con- 

 sisted of the following two displacements : 



(First motion): 2a = .5.0mm., direction S G6° W. 

 (Second motion): 2« =3.1 mm., direction N 46° E. 



The principal vibration of the V.M., Avhose average period 

 was 0.9 second, occured simultaneously, but did not synchronize, 

 with those of the H.M. The maximum 2a of the V.M. was 

 1.3 mm., its period being 0.9 second. 



In the end portion, the average period of ripples was 0.09 

 second in the (EAV), and 0.06 second in the (V). 



It may here be noted that the direction of the maximum 

 vibration, namely S 79° W — N 79° E, pointed exactly towards 

 the epicentre of the earthquake. 



7. Eqke. No. 4. The 31st August, 1896; 5.9.55 p.m. In- 

 tensity, very strong. This was the great earthquake, which caused 

 much destruction in the eastern part of the Province of Ugo 

 and the western part of the Province of Pikuchu, the origin 

 being at about 100 km. S 80° W of Miyako. 



