EARTHQUAKE MEASUREMENT AT MIYAKO. 175 



after the beginning, the average period was 0.094 second in the 

 (EW), and 0.081 second in the (NS). There were also some 

 slight traces of slow undnlations. 



16. Eqke. No. 12. The 18th June, 1897 ; 1.18.5 p. m. 

 Intensity, strong. The origin was evidently in the vicinity of 

 the observing station, probably near to the sea-coast, at about 

 90 km. SE of Miyako. 



The duration of the H.M. was 50 seconds. The V.M. 

 was evidently very considerable, but was unfortunately not re- 

 corded, the pointer of the vertical motion seismograph having 

 been thrown off the record-receiver immediately after the termi- 

 nation of the preliminary tremor. 



The preliminary tremor, whose duration was 8.5 seconds, 

 consisted of ripples of the following elements. 



It is to be remarked that during the preliminary tremor, 

 the motion was much greater in the horizontal than in the 

 vertical component, and again about twice as great in the (NS) 

 as in the (EW). Further, the motion remained nearly constant 

 throughout this epoch, the amplitude being not smaller in the 

 beginning than in the^later portion. 



In the principal portion, whose duration was 9 seconds, the 

 motion was about twice as great in the (EW) as in the (NS), 

 the average period being longer than that in the preliminary 

 tremor, namely, 0.11 second in the (EW), and 0.10 second in 

 the (NS). The most active movement was limited to the first 

 2.3 seconds of the principal portion, and the mean direction 



