地震動観測記録と有限差分解析に基づく中京地域で観測される長周期地震動の震源位置依存性に関する研究

Abstract

Recently, it is said that the characteristics of ground motions on the irregular sedimentary basin structure vary depending on the incident direction of the seismic wave. The incident seismic waves are affected by the path, and have a different nature depending on the source location. Therefore, it is important to focus on the source location and to consider the path effect. In this study, the long-period ground motion by the earthquakes in 3 zones (Off-Sanriku, Off-Kii Peninsula, and the Niigata sedimentary basin) are compared in the path effect and the site effect. Especially, the ground motion at the site near the seismic source and outside the Chukyo sedimentary basin have different nature. The result shows that long duration and long-period seismic wave propagates to Chukyo area in the case of an earthquake in the Niigata sedimentary basin zone and Off-Kii Peninsula zone, compared with Off-Sanriku zone. It is known that strong long-period seismic wave propagates to Chukyo area due to the sedimentary wedge, if an earthquake occurs in Off-Kii Peninsula zone. On the other hand, strong long-period seismic wave from the Niigata sedimentary basin zone is considered to be affected by the Niigata sedimentary basin. By using the 3D finite difference method, the same phenomena were simulated for 5 earthquakes in the Niigata sedimentary basin zone. If the seismic wave do not pass the Niigata sedimentary basin, the long-period ground motion is not caused in Chukyo area. Therefore, the earthquake beneath the Niigata sedimentary basin could radiate long-period seismic wave to Chukyo area from the northern part of Nagano Prefecture. In addition, 3D finite difference analysis based on the reciprocity theorem of Green's function is applied to the bedrock site between the Niigata sedimentary basin and Chukyo area. The sedimentary basins on the seismic wave path including the Niigata sedimentary basin affect the seismic wave. The sedimentary basins cause an increase of the amplitude and extension of the duration time of the seismic wave, and some of them cause an increase of the amplitude at the specific period range. It is suggested that these effects may be different depending on the shape and the size of the sedimentary basin and the seismic wave paths. According to the above mentioned result, the damage of specific long-period building could be larger depending on the source location. It is important to evaluate the path effect including the sensitive period range and the site effect together.