11:00 AM - 1:00 PM
[SSS10-P15] Effects of Seasonal Frozen Soil on Ground Motion Amplification
from Strong Motion Records in Vertical Arrays
Keywords:seasonal frozen soil, ground motion amplification characteristics, spectral ratios, surface layers, S-wave velocity
In this study, we examined effects of seasonal frozen soil on ground motion amplification characteristics through numerical experiments and analysis of strong motion records of the KiK-net, Japan. We studied the seasonal variation of the temperature in Hokkaido, to determine target areas and a period when the ground is expected to freeze for our examination of the seasonal changes in the spectral ratios of the strong motion records of the ground surface to those of the bottom of the vertical arrays.
Firstly, we examined seasonal changes of S-wave amplification characteristics through numerical experiments with two-layers shallow soil models. The results show that the larger the ratios of the thickness of the frozen part to total thickness of the soil layer are, the larger the changes in the spectral ratios are. The changes of the spectral ratios are also related to the S-wave velocity of the soil layer. It is also pointed out that the changes of the ratios are discussed separately for each mode of the amplification factors to know their relations with the S-wave velocities of the surface layers.
Secondly, we examined the seasonal changes of the spectral ratios using strong ground motion records observed at the stations of the KiK-net in the eastern part of Hokkaido, Japan, with a comparison to the results of the numerical experiments. We could not find no significant relationships between the ratios of the thickness of the frozen part (with assumption of 1m) and the seasonal changes. After a classification by the target mode of the amplification factors, we found that the relationship between S-wave velocities of surface layers and the seasonal changes, especially the difference in the peak frequency, is similar to that of the calculation. However, there are some differences from the results of the calculation. The results indicate the necessary of examining the physical properties other than the thicknesses of frozen parts and S-wave velocity of the surface layers.
Acknowledgements
We used the observation data from the KiK-net, Strong-motion Seismograph networks of the National Research Institute for Earth Science and Disaster Resilience, NIED.
Firstly, we examined seasonal changes of S-wave amplification characteristics through numerical experiments with two-layers shallow soil models. The results show that the larger the ratios of the thickness of the frozen part to total thickness of the soil layer are, the larger the changes in the spectral ratios are. The changes of the spectral ratios are also related to the S-wave velocity of the soil layer. It is also pointed out that the changes of the ratios are discussed separately for each mode of the amplification factors to know their relations with the S-wave velocities of the surface layers.
Secondly, we examined the seasonal changes of the spectral ratios using strong ground motion records observed at the stations of the KiK-net in the eastern part of Hokkaido, Japan, with a comparison to the results of the numerical experiments. We could not find no significant relationships between the ratios of the thickness of the frozen part (with assumption of 1m) and the seasonal changes. After a classification by the target mode of the amplification factors, we found that the relationship between S-wave velocities of surface layers and the seasonal changes, especially the difference in the peak frequency, is similar to that of the calculation. However, there are some differences from the results of the calculation. The results indicate the necessary of examining the physical properties other than the thicknesses of frozen parts and S-wave velocity of the surface layers.
Acknowledgements
We used the observation data from the KiK-net, Strong-motion Seismograph networks of the National Research Institute for Earth Science and Disaster Resilience, NIED.