242 



hepout — 1884. 



I fim glad to liavc it in my power to say are now being published by tlie 

 Seisnioloffical Sociiefy. 



The results -wbicli these obsorvat ions have ^iven, al(honi,'h in certnin 

 cases only eonfiiinatory of previons observaiions, may be epitomised as 

 follows : — 



1. Out of the ;iH7 shocks, 2o4 have been local, the area shaken in 

 some cases not exceedinfj .^n s(iuiu'(! miles. 'I'lie remftinini^ 13.'J disturb- 

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

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

 miles, As the latter originated far out at sea their efTeets on the land 

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

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

 vera 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 Toncgawa, especially near its month, which is ono of the 

 flattest parts of Japan. Is^o less than eighty-four jier 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 arc 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 crossiug them. The 

 mountains referred to are broad ranges, having i)caks 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 distiibtition 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 bren ejected to foi-m 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. 



o. Of the o87 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, thou 

 the seismic energy of the winter month.s to that of the; summer months 

 is in the ratio 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 seisuio- 

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

 ceedingly imperfect), have given for the whole world. 



4. Taking 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, wc find that their occurrence closely 

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

 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 tlio 

 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. 



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