EARTHQUAKE MEASUKEMENT AT MIYAKO. 165 



The motion, which, as in No. 1, consisted of slow undula- 

 tions almost perfectly free from superposed ripples, was about 

 2o times greater in the EW than in the NS component, the 

 V.M. being also present. The duration of the H.M., as well as 

 that of the V.M. was 56 seconds. 



The 'preliminary tremor, whose duration was 13 seconds, 

 consisted of very small slow undulations of an average period 

 of 0,86 second. 



The maximum vibration, whose period was 1.7 seconds, 

 and which occurred at the beginning of the principal portion, 

 consisted of the following two displacements : 



(First motion): 2.8 mm. towards E, 0.9mm. towards, N and slightly 

 upwards. Resultant 2a = 2.9mm., direction E 25° N. 



(Second motion) : 3.8 mm. towards W, 1.4 mm, towards S, and 

 0.3 mm. downwards. Resultant 2a = 4.1 mm., direction W 25° S, 

 the angle of emergence = 4°. 



The average period of the seven small vibrations, which 

 followed the maximum motion, was in the (EW) 0.82 second, 

 and in the (NS) 0.77 second. At about 21 seconds from the 

 commencement there was a second maximum epoch, which con- 

 sisted of three nearly equal undulations of an average period 

 of 1.4 seconds, the two displacements of the first vibration being 

 as follows : — 



(First motion) : 0.7 mm. towards E, 0.2 mm. upwards. Resultant 

 2« =0.7 mm., direction E, the angle of emergence = 16°. 



(Second motion): 1.1mm. towards W, 0.3 mm. downwards. Resultant 

 2a = 1.1 nmi., du'ection W, the angle of emergence = 13°. 



The third maximum epoch occurred at about 27 seconds 

 from the beginning, the average period of vibration being 1.2 

 seconds in the (EW) and 1.0 second in the (NS). 



