Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

Digitization and Processing of J.M.A. Strong Motion Records 395R : arm length.C : position of the pivot of the arm.P1, P2, P3 : points which co-ordinate8 are read by a digitizer.---- . perpendicular bisector._____ : iso-time circle (all points on the circle should have the same time-readings).Figure 4. Method for estimating the arm length.sponding to the each stage (Figure 5b) were performed. In Figure 5b, C1, C2 andC3 indicate the distance between the true and apparent zero-line in each section,and R indicates the arm length. (2) The effects of finite arm length and inclinationof the arm were removed from the time history in each section (Figure 5c).4. Peak Ground MotionsFollowing the procedures mentioned in the preceding section, the equally interpolateddata of ground displacement for each component were obtained. Then, velocityand acceleration time histories were computed by once and twice differentiating thedisplacement time history. Peak values of ground motions for each component areshown in Table 3. In Table 3, the maximum value among the peak values is 23.3 cmfor displacement, 12.8 kine for velocity and 27.7 gal for acceleration.5. Velocity Response Spectra and Seismic Design SpecificationsThe velocity response spectra, Sv, of each component for the period range of 2 to20 sec with damping factors, h, of 0.1% and 2% were computed. The value h of0.1% corresponds to the sloshing of oil storage tanks and 2% to steel structuressuch as suspension bridges. Examples of the response spectra, Sv, whose levels arerelatively large, are shown in Figures 6 to 8.