126 



S. SEKIYA AND Y. KIKUCHT 



to the west near the coast of the Japan Sea. 



On the morning of the 15th, at a little after 7, a feeble earthquake 

 occurred, but it was so slight that many failed to notice it. After 

 half-past seven a severer shock ensued, lasting nearly 20 seconds. 

 This was followed soon after by very violent convulsions of the 

 ground; houses rocked and swayed, furniture fell down, and the 

 frightened people felt the ground heaving beneath their feet. It was 

 reported that the nature of this earthquake differed from that usually 

 experienced, in that vertical motions greatly predominated. The 

 shock was a long one, lasting, according to some accounts, for fully 

 a minute. While it was still in progress the eruption took place. 

 Considering the fierceness with which this earthquake shook the im- 

 mediate vicinity of the mountain, it is remarkable that the intensity 

 was very rapidly decreased as the seismic waves were propaged into 

 the surrounding region, and the shaken area was limited to a radius 

 of, roughly speaking, about 48 kilometres, or 30 miles. This may be 

 accounted for by the fact that the origin of the shock was rather near 

 the surface. On PI. XXIV the boundary of the area shaken by the 

 earthquake is shown by a thick elliptical line. 



Volcanic eruptions are generally accompanied by earthquakes, 

 and the shocks on this occasion prove that sudden expansion of steam 

 and breaking up of the earth's crust may produce seismic vibrations. 

 The efforts of the pent-up steam, struggling to force its way through 

 the superincumbent masses, at last succeeded in bursting through a 

 weak point, the explosion being accompanied by violent convulsions 

 of the ground, that were propagated as seismic waves. 



On the 20th of July, at 11.50 a.m., a feeble shock was ex- 

 perienced. Other minor shocks are said to have subsequently occurred. 



To see whether the ground in the crater was perfectly quiet 

 after the eruption, we took with us a delicate though somewhat 



