EARTHQUAKE MEASUREMENT AT MIYAKO. 185 



The preliminary tremor was not recorded, having probably 

 been lost on account of its feeble intensity. The maximum 

 motion, which occurred at the commencement, was 2a = l.l mm., 

 direction N 60° E. 



32. Eqke. No. 24. The 23rd April, 1898 ; 8.34.13 a. m. 

 Intensity, strong. The origin of this extensive earthquake was 

 situated probably at about 200 km. ESE of Miyako. 



The duration of the H.M. was about 120 seconds. The 

 V.M. was recorded till 20 seconds from the commencement, 

 when the motion became very large and the pointer went off 

 the record-receiver. 



The preliminary tremor, whose duration was about 13 

 seconds, and whose range of motion was greatest in the (NS), 

 consisted of ripples of the following elements : — 



The ripples were, as is usually the case with strong shocks, 

 superposed on slow undulations. 



The principal portion, whose duration was 19 seconds, was 

 unfortunately vitiated by the proper oscillations of the seismo- 

 graph pendulums. The average period of the ripples has, 

 however, been mensured and found to be 0.11 second in each 

 horizontal component, the elements of the largest ripples being 



(First vibration): 2a = 6.4mm., T.— 0.1.5 second, direction NE. 

 (Second vibration): 2a = 5.4 mm., T =0.18 second, direction N .30° E. 



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

 0.06 second in the (EW) ; these being superposed on slow 



