Abstract
The long-period (2 to 15 sec) ground motion caused by the 1923 Great Kanto Earthquake was investigated to obtain more detailed information for the seismic design of long-period structures, especially those constructed in the Tokyo area. In order to investigate the main shock ground motion, the incomplete seismogram obtained by the Imamura type strong-motion seismograph at the University of Tokyo was used. To examine the behavior of the pendulum system and to find the cause of saturation, shaking table tests were carried out for the Imamura type seismograph, which has been exhibited at a museum. Applicablity of the method for mending the saturated waveforms was found and confirmed through numerical experiments. The following restoration and correction were performed: (1) mending of the saturated waveforms of the incomplete main shock seismogram and (2) correction of instrument response of the seismograph. The main results of this study can be summarized as follows: 1) The peak ground amplitude of the 1923 Great Kanto Earthquake in central Tokyo was about 15cm in the E-W component. 2) The duration of significant portion of the main shock ground motion was as long as 10 minutes. 3) The peak amplitudes of the velocity response spectrum with a damping factor of 0.01 was 80 cm/s for the E-W component. 4) The ground motion in the N-S component is presumed to have been about 1.5 times larger than that in the E-W component.
