242 eepobt — 1884. 



I am glad to Lave it in my power to say are now being published by tlie 

 Seismological Society. 



The results which these observations have given, although in certain 

 cases only confirmatory of previous observations, may be epitomised as 

 follows : — 



1. Out of the 387 shocks, 254 have been local, the area shaken in 

 some cases not exceeding 50 square miles. The remaining 133 disturb- 

 ances each shook an area with an average diameter of 45 miles. A few 

 of the larger shocks shook an area the radius of which was at least 150 

 miles. As the latter originated far out at sea their effects on the land 

 were small. At least fifteen cases have occurred when an earthquake 

 has been practically felt at the same time over two distant areas — obser- 

 vers in the intermediate areas not having felt any disturbance. The 

 distance between such areas has been as much as 150 miles. 



2. The area where the most earthquakes have been felt is along the 

 line of the Tonegawa, especially near its mouth, which is one of the 

 flattest parts of Japan. No less than eighty-four per cent, of all the 

 earthquakes observed have originated beneath the Pacific Ocean, or on 

 the land close to the sea-board. 



The volcanic regions of Japan and the mountainous districts are sin- 

 gularly free from earthquakes. 



Unless an earthquake is very severe it invariably grows feebler as it 

 approaches the mountains and then dies out without crossing them. The 

 mountains referred to are broad ranges, having peaks from 6,000 to 

 10,000 feet in height. 



In many respects the distribution of seismic activity in Japan holds a 

 close relationship to the distribution in South America. In the centre of 

 Japan we have high mountain ranges consisting of granite, metamorphic 

 slates and limestones, and old volcanic rocks, perforated by the vents 

 from which materials have been ejected to form modern volcanoes. 



The mountains to the eastward slope steeply beneath a deep ocean, 

 whilst to the west there is a very gentle slope. The earthquakes chiefly 

 originate on the steep slope beneath the deep ocean. In South America 

 many of the destructive earthquakes appear to have had a similar origin. 



3. Of the 387 earthquakes, 278 occurred during the winter months 

 and 109 during the summer months. If, for convenience, we consider the 

 intensity of an earthquake as being proportional to the area shaken, then 

 the seismic energy of the winter months to that of the summer months 

 is in the I'atio of about 3:1. 



In the whole of Japan on the average there is at least one shock per 

 day, possibly two or three. This is a number which European seismo- 

 logists, basing their calculations on catalogues (which for Japan are ex- 

 ceedingly imperfect), have given for the whole world. 



4. Takiug either the 387 earthquakes here referred to, or the records 

 of earthquakes made during the last ten years in Tokio, by means of 

 instruments working automatically, we find that their occurrence closely 

 follows curves of temperature. A peculiarity is that the sinuses of the 

 curves of mean monthly temperatures are generally a little in advance of 

 the crests of the waves indicating the frequency of earthquakes. In con- 

 nection with this observation attention may be drawn to the fact that the 

 curves of temperature are those for the air, whilst many of the earth- 

 quakes originated beneath the ocean, which gains temperature slowly and 

 loses it slowly. 



