ON THE EARTHQUAKE PHENOMENA OF JAPAN. 241 



Fourth Report of the Committee, consisting of Mr. K. Etheridge, 

 Mr. Thomas Gray, and Professor John Milne (Secretary}, 

 appointed for the purpose of investigating the Earthquake 

 Phenomena of Japan. Drawn wp by the Secretary. 



DrniNG the last year, that is, from Jane 1§83 to the end of May 18£4, 

 only thirty-nine earthquakes have heen recorded in Tokio. In the three 

 previous years during corresponding periods the number of records were 

 75, 57, and 28. Not only have the shocks been few in number, but they 

 have also been unusually feeble. At the time when the greatest shocks 

 occurred, which was at the end of December and in January, I was 

 absent from Tokio on a visit to the Takashima Colliery, near Nagasaki, 

 with the object of establishing an underground observatory. 



Although, as these remarks indicate, my opportunities for the obser- 

 vation of earthquakes have been small, I am pleased to state that I have 

 been singularly fortunate in obtaining a series of most interesting records, 

 and at the same time have had leisure to work up a portion of the nu- 

 merous observations which during the last few years have been steadily 

 accumulating. A few of the results which have been obtained have 

 already been communicated to the Seismological Society. These, together 

 with others which yet remain for publication, are briefly as follows : 



Determination of areas from which the shalcings so often felt in North Japan- 

 emanate. 



In my report to the British Association in 1882, I stated that I had 

 sent bundles of postcards to all the important towns within a radius of 

 sixty to one hundred miles of Yedo, with a request that every week one 

 of these cards should be returned to me together with a statement of the 

 earthquakes which had been felt. Subsequently the boundary of the 

 postcard area was extended until it covered the whole of Japan north of 

 Tokio. I did not extend the area far towards the south, because I quickly 

 discovered that it was seldom that earthquakes originated in that direction 

 whilst disturbances travelling from the north towards the south quickly 

 died out as they reached heavy mountain ranges which in that part of the 

 country had a strike at right angles to the direction in which the dis- 

 turbances were travelling. At the end of September 18S3, after exactly 

 two years of observation, I ceased to supply my correspondents with 

 postcards and commenced the arrangement and analysis of the accumu- 

 lated material. From regular observers I found that I had received 

 about 1,500 letters, whilst there were also a large number of others from 

 casual correspondents. I also had the records of instruments placed in 

 various parts of the country, and a very extensive series of diagrams and 

 notes made by myself and others in Tokio and Yokohama. 



In the two years I refer to, in North Japan and Yezo 387 earthquakes 

 had been noted. Of each of these I was enabled to draw a map showing 

 the area over which it had been felt, and to indicate approximately its 

 origin. In the determination of origins I was greatly assisted by the 

 records of instruments and the time observations which had been checked 

 by daily time signals sent by the Telegraph Department from Tokio. 

 One hundred and twenty-five of these maps drawn on a small scale 



1884. R 



