ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 219^' 



is at right angles to a well-defined axis of rock cmmpling, whicli shows 

 itself in the N.W. to S.E. strike of the mountains some thirty miles 

 distant, and which line of folding probably continues beneath the plain of 

 Tokio. 



Another point not to be overlooked is that the direction of earth- 

 quake motion across the Tokio plain is in the majority of cases also at 

 right angles to the direction of mountain strike. During the next 

 summer I shall endeavour to instal horizontal pendulums on the rocks 

 themselves, one of them parallel to the dip and the other at right angles 

 to this direction. 



Irregular Movements. 



It often happens that superimposed upon the daily wave there are 

 sinuosities with amplitudes of 1" or 2". These appear to be chiefly 

 marked on the east and west components of the diagrams. They have 

 periods of from three to six hours, and generally occur as a sinking 

 during the early morning or between midnight and 8 or 9 a.m., at which 

 time the east is usually rising. 



On February 17, March 24 and 26, small earthquakes occurred witb 

 these sinkings, after which the normal rise was continued. Other earth- 

 quakes, which, however, were too small to be measured by ordinary 

 seismographs, were not accompanied by such changes. Before the 

 earthquake of March 6, which probably was of local origin, the spots of 

 light had moved off the scale as if by an abnormally large sinking on the 

 N.E. side. This was at 8.45 p.m. on March 5. I therefore do not know 

 what happened immediately before the shaking, which took place at 

 8.52 A.M. next morning. 



Earth-waves or Earth-pulsatiotis. 

 (Tremors or Microseismic Disturbances.) 



On February 17, 18, and 19 there was a large and well-marked storm 

 of tremors. The barometer did not fall to any remarkable extent, the 

 lowest I noted being 297 in. While the movements were continuing 

 the east side of the column was depressed about 2", and the daily wave 

 did not show itself. With other tremor-storms, which were, however, 

 smaller, the daily wave has been unaffected. 



Earthquakes. 



From the list of earthquakes at the commencement of this report it 

 will be seen that during the months of February and March nine earth- 

 quakes were recorded at the Central Observatory in Tokio. Five of 

 these were measurable by seismographs. Seven out of the nine were 

 recorded at the University Laboratory, which is about 1^ mile distant 

 from the central station. Owing to certain of these having occurred 

 when there had been a temporary interruption in the taking of records — 

 as, for example, when changing a film— it is only possible that three of 

 the seven disturbances should have been photographically recorded. 



These records are remarkable for their smallness, apparently showing 

 that, although there had been a sensible motion of the ground, the 

 mirrors had either remained practically at rest, or else they had not been 

 movmg for a sufficiently long period of time to produce an impression on 

 the film. As the films, which were prepared for me by Professor W. K. 



