2021 Volume 21 Issue 4 Pages 4_21-4_33
It is known that seismic ground motion is locally amplified in irregularly layered ground such as valleys and cliffs. In the southern part of Kanto region, there are many Holocene valleys through terraces, called "Yatsu." In such areas, the risk of disasters during an earthquake will be high. In this study, seismic observations were conducted for three Holocene valleys in Chiba Prefecture. The records at the center part of valleys show different characteristics compared to those of other part of valleys depending on direction. In order to investigate those phenomena, two dimensional analyses of the three valleys were conducted. The models of 2D analysis were created based on the ground survey. The results of the analyses show good agreements with the seismic records. It is shown that the seismic ground motions at Holocene valleys were affected by the subsurface irregularly layered soil structures.
