152 



F. OMOEI : 



5* 



7* 



Strong. 



Weak. 



Stron£ 



Weak. 



0. 49. 28 a. ni. | (The severe Nagano 



Eqke.) 170 kil. 



N.W. 

 9. 12. 23 a. m. In the ocean, about 



400 kil. N.E. 

 2. 59. 57 a. m. (The severe Echigo 



Eqke.) 170 kil. 



N.W.N. 

 8. 37. 00 a. m. In the ocean, about 



400 kil. N.E. 



17. seconds. 



45. 



17. 



54. 



The positions of the suboceanic origins of the two earth- 

 quakes, No. 5 and No. 6, (marked with asterisks), have been 

 inferred simply from the forms of their isoseismal lines on land 

 and are, therefore, to be regarded as being only approximate. 

 These two earthquakes have been excluded in deducing equation 

 (1) below. With respect to the remaining five earthquakes, all 

 of which, except No. 2, originated inland, the positions of their 

 origins have carefully been determined from special investiga- 

 tions and are consequently to be regarded as being exact. 



I add here the observation at the Meteorological Obser- 

 vatory of Osaka^ of the great Mino-Owari earthquake of the 

 28th October, 1891 : 



{(Distance of Osaka from the origin = 140 kilometres.) 

 Duration of the preliminary tremor = 14 seconds. 



7. Comparing the results in § § 2, 3, and 4 with that in 

 § 6, we see that the duration of the preliminary tremor of an 

 earthquake depends on the distance between the origin and the 

 observing station, the average durations being for the obser- 

 vations at Gifu, Kagoshima and Fukuoka, respectively only 

 1.4, 2.0 and 0.2 seconds. Whether the duration of the prelimi- 

 nary tremor would actually vanish at the very centre (not the 



1. At Gifu and Nagoya, much nearer to the origin, the durations of the preliminary 

 tremor of the same earthquake were respectively 2 and 4 seconds. 



