156 REPORT— 1895. 



calculate, not only the numljer of .shocks which will be experienced before 

 the district settles to its normal state of seismic activity, but also the 

 interval of time that will be involved in such an operation. For the 

 earthquakes considered by Mr. Omori it may be concluded that the 

 earth's crust had been so far fractured that there was an approximate 

 •similarity in the heterogeneity of the disjointed material, which tliere- 

 fore, as it settled, gave rise to after shocks following a somewhat similar 

 law. Another observation was that the larger of the after shocks 

 travelled to greater distances than their smaller companions, and in con- 

 sequence there was a marked difference in frequency at places situated 

 ■at different distances from the primitive origin. If there is any law in 

 this decrease in frequency with distance, then the frequency of what are 

 evidently after shocks observed upon a coast line, as in Districts 1 and 10, 

 might enable an observer to make a rough estimate of the distance of 

 an inaccessible submarine origin. That satisfactory results would be 

 obtained from such an investigation is, however, doubtful. 



Distribution of Earthquakes. — An inspection of the map of earth- 

 quake origins or centres shows that the central portions of Japan, which 

 ■fire the mountainous districts where active volcanoes are numerous, are 

 singularly free from earthquakes. The greater number of disturbances 

 originate along the eastern coast of the Empire, and many of these have 

 .a submarine origin. That very few earthquakes are shown on the coast 

 line between Districts 1 and 2 is in a great measure due to the fact that 

 in this region there are but few observing stations, the island of Yezo 

 in which these districts are situated being sparsely populated. A line 

 drawn from N.N.VV. to S.S.E., or from numbers 7 to 5.57, is the chief 

 ■anticlinal axis of the northern island, and from the southerly prolonga- 

 tion of this beneath the ocean, earthquakes from time to time originate, 

 which shake, not only the eastern coast of Yezo, but also many of the 

 districts on the main island. Although districts like 11, 9, 8, and then 

 through 7, suddenly northwards up to 13 or 14, lie along the strike line 

 of the southern portion of the Empire, a greater number of earthquakes 

 seem to originate from the face of the steep monoclinal .slope which Japan 

 presents towards the Pacitic Ocean. 



Lines, 120 geographical miles in length, running in an easterly or 

 south-easterly clirection from the highlands of Japan into the Pacific 

 Ocean, like similar lines drawn from the Andes westwards into the same 

 •ocean, have a slope of 1 in 20 to 1 in 30, and in both of these districts 

 earthquakes are frequent. On the contrary, along the face of flexures 

 which are comparatively gentle, being less than half these amounts, which 

 may be seen along the borders of most of the continents and islands of 

 the world, earthquakes are comparatively rare. The inference from this 

 is that, where there is the greatest bending, it is there that sudden 

 yielding is the most frequent. In the case of many of the Japanese 

 •earthquakes, this takes place along the face of a monoclinal feature of 

 the world's surface, and the intimate relationship between monoclines and 

 .faults is known to all geologists, the former being, in the words of Sir 

 Archibald Geikie, an incipient stage of the latter. 



Earthquakes and Secular Movements. — Another feature indicated by 

 *he map or known to the writer from personal observation is that earth- 

 •quakes are frequent in those districts where there are evidences of secular 

 •elevation or depression, that is to say, in those di.sti'icts where movement 

 -of the earth's crust is yet slowly taking place. 



