114 



F. ÖMORI. 



the initial shocks. In the case of the Kagoshima earthquake, there 

 was a second great shock about four months after the first, but the 

 two had quite different origins.^ 



The frequency or activity- of after-shocks at a given distance 

 from the origin is different for different earthquakes, and depends 

 mainly on the magnitude of the initial shock, and at the epicentre, 

 of course on the depth of the focus also. I may here state that the 

 focal depths of the three great earthquakes we are discussing were all 

 comparatively very small, being probably between 2 and 4 ri. 



§ 7. The tal)le following will serve for making a comparis(jn of 

 the frequency and activity of tlie after-shocks of the three earth(piakes 

 as observed at or near the epi-f^-i of the latter in the days immediately 

 succeeding the initial shocks : — 



The Kumam«3to earth({uake took place on July :^<Sth, 1<S8!), at 

 lib. 4 Dm., p.m.; the Mino-Owari earth(|uake, on October 2.Sth, 

 1<SD1, at 6h. 37m., a.m.; and the Kagoshima earthquake on Se})tember 

 7th, 1803, at 2h. 4()m., a.m. Though the frequencies and activities 

 of the first three groups, (I), (II), and (III), in the al)Ove table, which 



1 See § 32. 



2 " Frequency " means the number, and " activity " the total intcusiti/ defined as iu § 2, of 

 shocks during any given interval of time. 



