EARTHQUAKE MEASUREMENT AT MIYAKO. 169 



8. Eqke, No. 5. The 31st August, 1896 ; 7.20.52 p. m. 

 Intensity, weak. The origin of the earthquake was evidently 

 in the vicinity of the observing station, the V.M. existing to a 

 proportionally large amount. Owing, however, to the irregular 

 distribution of the intensity of motion, it is difficult to determine 

 exactly the position of the epicentre. 



The duration of the H.M., as well as that of the V.M. 

 was 50 seconds. 



The prelimiîiary tremor, whose duration was 5.7 seconds, 

 consisted of very fine ripples of an average period of 0.054 

 second in the (EW), and 0.043 second in the (NS) ; these being 

 superposed on slow undulations of an average period of 0.86 

 second in the (EW), and 0.87 second in the (NS). 



The preliminary tremor was abruptly followed by the prin- 

 eipal portion, whose H.M. was much greater in the (NS) than 

 in the (EW). The maximum vibration, whose period was 0.56 

 second, consisted of the following two displacements : 



! (First motion), 1.2 mm. towards S, 0.6 mm. towards E. 

 Resultant 2a = 1.3 mm., direction S 30° E. 



{(Second motion). 2.1 mm. towards N, 0.6 mm. towards W. 

 Eesultant 2« = 2.2 mm., direction N 20° W. 



The mean direction of motion was thus S 25° E — N 25° W. 



The maximum V.M., which did not perfectly synchronise 

 with the H.M., was 0.3 mm., its period being 0.53 second. 



The average period of the ripples in the principal portion 

 was 0.054 second in the (EW), 0.056 second in the (NS), and 

 0.055 in the (V) ; these being superposed on the slow undulations 

 of an average period of 0.68 second in the (EW), 0.58 second 

 in the (NS). and 0.32 second in the (V). 



