176 F. OMORI AND K. HIRATA I 



of motion, whose maximum la was 7.4 mm., was N 60° Yj — 

 S 60° W. 



In the end "portion, the period became again a little shorter. 



17. Eqke. No. 13. The 5th August, 1897 ; 7.10.47 a. m. 

 Intensity, loeah. This extensive earthquake originated under 

 the ocean, probably at 220 km. SE of Miyako, the epifocus 

 being evidently linear and running nearly parallel to the 

 coast. 



The duration of the H.M. was 200 seconds, and that of 

 the V.M. was 150 seconds. In the preliminary tremor, the 

 motion was equally pronounced in the two horizontal com- 

 ponents ; but in the principal and the end portions, it was much 

 larger in the (EW) than in the (NS), and consisted of small 

 ripples superposed on slow undulations indicative of a distant 

 origin. 



The 'preliminary tremor, whose duration was 22 seconds, 

 consisted of ripples of an average period of 0.07 second in the 

 (EW) and 0.06 second in the (NS) ; these ripples being super- 

 posed on slow undulations of an average period of 0.8 second 

 in the (NS). 



The principal portion, consisted of ripples whose maximum 

 2a was 0.4 mm. im each component, and whose average period 

 was 0.087 second in the (EW), 0.080 second in the (NS), and 

 0.075 second in the (V). The period of the ripples remained 

 nearly constant throughout the duration of the shock, these 

 being superposed on slow undulations of an average period of 

 0.82 second in the (NS), (uncertain in the (EW) ), and 0.7 

 second in the (V). One of the largest of these slow undulations 

 in the (NS) had the maximum 2a of 1.8 mm., its period being 

 0.74 second. The corresponding movement in the (EW) was 



