284 



SEKIYA AND OMORL 



(ir.) IJipple-s. 



Average for both 

 Comj)oneats. 



2.2 



0.8 



2.8 



4.7 



It will 1)e tliiLs observed tliut for principal iindiiLitions of severe 

 eartli(|iiake.5 tlie raiii^e of motion is somcwliat o-reater on the surface 

 than in the pit, Ijiit there is no great difference of inaxiniiiin velocities 

 and niaxiinuni accelerations Ijetween the two sets of observations. 

 This seems io he due to the fact that for the larger nndulatic^ns tlie 

 period will .'.omewhat increase with the amplitude. In fict, tal)le (I.) 

 would ap[)ear to iiidic:he some slight increase (of period on the surface. 

 Tlie case is different with ripples, for which tlie results are more 

 uniform and llie difference of surfice and imderground effects more 

 decided. From Taljle (H.) the average extent of liorizontal motion in 

 the pit is only half that on the surface gnnind, and the period for 

 the former seems rather greater than f )r the latter, which arises 

 from the fict that veiy many of the ripples disappear in the pit. Tlie 

 maximum velocities and maximum accelerations on the surface are 

 respectively ahout tliree and live tunes those in the pit. 



Our conclusion tlien is that for small eartli(|iudves there is no 

 practical difference between the surfice and undergr(3uiid ol^servutions ; 

 for the principal undulations of severe eartlujuakes this difference 

 may exist, L>ut not to any marked degree ; but for the small quick 



