Evaluation of aggravation factors for seismic response of unfavorable sections based on strong-motion data

Abstract

Quantitatively exploring the classification of seismic unfavorable sections and seismic amplification are important research subjects in the field of earthquake engineering. Based on high-accuracy digital elevation model (DEM) data, landform classification map, and borehole section data, a total of 696 KiK-net stations in Japan were subjected to the classification of seismic unfavorable sections in this study. Next, 54,962 groups of 5–20-gal weak motions records and 1,984 groups of >100-gal strong motions records of such KiK-net stations during 1999-2021 were collected. Then, the average amplification of the acceleration response spectrum on the ground surface and the bottom of boreholes in each station under a damping coefficient of 5% in case of strong and weak motions was calculated. Results revealed that seismic unfavorable sections were characterized by an increasing amplification factor and widening response spectrum platform, and this amplification feature was more obvious at softer sites. Relative to weak motions, strong motions could further excite the terrain amplification of local protuberant sections and substantially increase the width of the response spectrum platform. For soft sites, the difference between strong and weak motions in the amplification factor was not evident. Moreover, the average amplification factor of seismic unfavorable sections basically coincided with that (1.1-1.6) specified in relevant seismic design codes. When a site was subjected to simultaneous intense terrain amplification and soil layer amplification, a greater site amplification might be triggered by the two amplifications if coupled, thus leading to a serious earthquake disaster.