EARTHQUAKE MEASUREMENTS OF KECEN'T YEARS. 7S 



Î« inaxiinuiii horizontal motion of 42 ni.ni. ^vith n complete period of 

 2 seconds was recorded at the above named place. 



When vertical motion occinTed it was invariably smaller than 

 the horizontal motion as is obvious from the first set of averajres. The 

 a\erage ratio of the two components of the motion was 1 to 6, or the 

 former was only one-sixth of the lattei-. 



The period of the vertical motion was shorter than that of the 

 horizontal motion. Their a^'era2■e ratio bein"- 1 to 1"8. That is 

 ■when the ground made one to-and-fro motion it also perf)rmed 

 during the same time nearly two complete up-and-down oscillations^ 

 Tn all the preceding tables the periods of the maximum vertical motion 

 are given, l)ut the periods in the other parts of the disturbances "were 

 much shorter. i'bey varied from 0*2 seconds to 0*5 seconds. 

 Exceedinolv feeble tremors of a few seconds duration îrenerallv 

 ]>receded the principnl motions as in the case of the horizontal 

 motions. 



The duration of the vertical motion was much shorter than that 

 of the horizontal motion. It occurred invariablv dnrina* the early 

 stages of the earthquake and generally ended before the horizontal 

 components. The average ratio of the two durations was 1 to 3^ 

 or the horizontal motion continued three times lon^'er than the 

 vertical. 



Tlie ^ertical motion almost invariably appeared when the 

 horizontal motion had reached 1 m.m. which was more than the 

 average amplitude in ordinary earthcpiakes. Out of 100 shocks there 

 were 18 cases in which the ground moved more than 1 m.m. Out 

 of these 18 earthquakes vertical motion occurred in 11 cases, or 78- 

 per cent, and did not appear in the remaining 4 cases. 



But on the other hand vertical motion also appeared in certain 

 cases when the horizontal motion was less than 1 m.m. Out of the 



