Comparison of Earthquake Measurements made 

 in a Pit and on the Surface Ground. 



By 



S. Sekiya, Professor, 



and 

 F. Omori, Ri'éakushi. 



Imperial University, Japan. 



In certain earthquake report« it is stated that there has been com- 

 paratively Httle or no movement felt at the bottom of a deep pit or 

 excavation, while 2:reat damasse was done on the surface of the o^round* 

 and it seems to be generally believed that shocks are felt less intensely in 

 mines. It is not easy to make instrumental measurements in a mine, 

 and, in fiict, we have very little exact knowledge of underground 

 shakings. From a practical point of view, however, with reference t(j 

 the Imildin"- of houses, it is more interesting' to investio'ate the shakinirs 

 in pits or excavations such as might be made for foundations. The 

 only instance of such actual measurements as yet published, as far as 

 we are aware, is that described by Prof. John Milne in a paper entitled 

 "On a Seismic Survey made in Tokio in 1884 and 1885 " (Trans. 

 Seis. Soc. Vol. X.) He made observations in a pit 10 feet in depth, 

 whose bott(3m was dry and consisted of hard natural earth. Comparing 

 the maximum amplitudes, maximum velocities and maximum accelera- 

 tions obtained in the pit during tlie tolerably severe earthquake of 



* For iustauce, see Trans Seis. Soc. Vol. VIII. page 98. "The Earthquakes of Ischia." 



