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| | Abstract | | Uncertainty of seismic amplification characteristics was examined. using high-density seismic observation data conducted at the nuclear sites Using one point in the observation network as a reference point, the spectral ratio with other points was obtained. The obtained spectral ratio is not constant and varies from earthquake to earthquake. This variation means that the ground is not completely parallel stratified, and the degree of variation reflects the uncertainty of the seismic amplification characteristics in the upper ground than the seismic basement. As a result of examining the standard deviation (SD) of the variation and investigating its characteristics, SD increases with frequency and shows a characteristic approximately proportional to the logarithm of frequency. And, the average value of SD tends to increase with the distance from the reference point. Therefore, when considering the uncertainty of the input ground motion to the structure, it is necessary to pay attention to the above characteristics. |
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