2003 Volume 56 Issue 1 Pages 59-74
To understand the characteristics of seismic ground motions during the 1995 Hyogo-ken Nanbu earthquake in Higashinada area Kobe city, the effects of the underground structure at the edge of the sedimentary basin on seismic ground motion were investigated using observed moderate and weak earthquake motions. A later phase can be clearly identified after S-wave onset in southern part of this area, which was generated by 2D multiple reflection wave due to the effects of the underground structure. The result of simulations suggest that the distribution of synthetic maximum amplitude ratio referred to rock site depends on input motions. Due to the basin edge effects, the distribution of the maximum amplitude ratio shows a peak at the edge of the sedimentary basin using the sine wave with period of 1s and duration of 0.5s as an input wave. Besides, the ground motion of the 1995 Hyogo-ken Nanbu earthquake observed at Kobe Univ. was used as an input motion, which shows two peaks. One peak was located near the edge of the sedimentary basin and it was generated by the basin edge effects. The other one was generated by the interference between diffracted wave and 2D multiple reflection wave and it was located at the south border area with intensity VII determined by Japan Meteorological Agency. Our results indicate that the effects of 2D multiple reflection wave generated at the edge of sedimentary basin is important for the big earthquake motions.
