ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. \o7 



In Districts 1, 2, 5, 6, and 7 the writer knows from repeated obser^■a- 

 tion that there are evidences of very recent elevation, and certainly in 

 these districts earthquakes are extremely frequent. The signs + and — 

 in the neighbourhood of Districts 8, 9, 11, 12, and 13, and along the 

 Inland Sea, lying to the north of 8 and 9, but to the south of 12, also 

 show a like relationship. 



The only excejitions to the general rule appear to be the westerly 

 portion of the district between 12 and 13, where there are evidences of 

 secular movement, and earthquakes are of rare occurrence, and 1 in 5 

 cases where these conditions are I'eversed. The district No. 14 presents 

 a series of earthquakes originating along the line of a valley between 

 high mountains running from N.N.E. to S.S.W. Another good example 

 of earthquake fracturing following a line of weakness down a valley 

 between high mountains until it reached the plain was the disturbance 

 of October 28, 1891, which, as has been explained, resulted in the abnor- 

 mal conditions shown in District 7. 



In Japan, therefore, earthquakes have been frequent along the steep 

 monoelinal face of the countiy, in the synclinal trough of deep valleys, 

 possibly along the continuation of the Yezo anticlinal, and in districts 

 where secular movement is in progress. In Italy earthquakes originate 

 along the anticlinal of the Apennines, and from what we know of the 

 geological history of the country, which had its greatest growth in 

 Tertiary times, and from the bradyseismic movements on the coast, it 

 is not unliirely that the shakings it experiences announce the fact that 

 secular yielding is yet in progress. The earthquakes of Switzerland and 

 those which shake the Himalayan, and the younger mountains of the 

 world, may also be taken as due to orogenic causes which seem to be so 

 actively in operation in Japan. 



Earthquake Soiinds. — A map which has been prepared, but which has 

 not been reproduced Avith the catalogue, .shows the distribution of earth- 

 quakes accompanied by sound phenomena. To indicate that a sound was 

 heard, a dot is used, for a sound with a shock the sign -f , for a sound 

 before a shock the sign — , while for a sound after a shock the sign I . 

 After a volcanic explosion it might be expected that a sound wave 

 propagated through the atmosphere would succeed a trembling of the 

 ground. 



As the latter sign occurs but seldom, although there are one or two cases 

 of its occurrence in Districts 6, 7, 12, and 14, generally near active or old 

 volcanoes, and about two cases in District 8, it may be assumed that 

 earthquake sounds, rather than representing atmospheric waves radiating 

 from an epifocal area, represent elastic vibrations trani^mitted through 

 the ground, and therefoi-e arrive at a given station in advance of any 

 quasi-elastic surface undulation. Inasmuch as earthquake sounds only 

 travel a few miles from their origin, the intervals between them and an 

 earth movement which can be felt are very small. The result of this is 

 that it often appears that the two phenomena are simultaneous, and 

 therefore on the map we find nearly as many signs indicating 'sound with 

 ■ihock ' as those which indicate ' sound before shock.' Sounds are often 

 hsard which cause people to run from their houses, expecting a shock 

 which does not come. The dots on the map represent sounds which have 

 been to ordinary observers simultaneous with an actual shaking of thft 

 frrounrl. Taking the districts in order, we find the sound phenomena 

 distributed as follows :- 



