On the Seismogram

[摘要] It is a well known fact that Seismogram is greatly disturbed by the free oscillation of the penduium, when no damping is introduced to it.In general, the displacement of the index point of a seismometer (ξ) is given bywhere n0 and n are the numbers of oscillation in 2n seconds, of the earthquake motion and that of the free oscillation of the pendulum respectively, if the displacement of the earthquake motion (x) is given byIf the earthquake occurs at t=0 and afterward a simple harmonic motion of ground continues indefinitely, i.e. if its displacement is given bythe apparent displacement of seismometer index is given bywhereThe author has computed the numerical values of the maximum displacement of the pendulum for first few oscillatious and corresponding phases. The results are given in table I and II in page 110, and graphically shown in fig. 1 and 2.The followings may be specially noticed:1. The amplitude of the first motion recorded is greatest for the oscillation with infinitely short period, 2. The amplitudes of the second and other oscillations are greatest for some periods of oseillation shorter than that of the free oscillation of the pendulum, 3. The free oscillation of the pendulum is larger than the forced oscillation, when the period of the earthquake motion is larger than that of the free oscillation. Accordingly, in this case no apparent relation is found between the earthquake motion and the motion recorded.

[学科分类] 大气科学