场地对地震动放大作用的方向相关性研究

现有场地对地震动的放大作用分析中，常采用观测得到正交方向的HVSR和SBSR的矢量合成结果表征场地放大作用，而不考虑放大作用的方向相关性。为研究不同地震作用下场地放大作用的方向相关性，采用多向HVSR和多向SBSR及谱比峰值方向相关分布概率，以11次地震事件获得的地表、井下基岩记录作为数据，开展响嘡场地效应台阵场地对地震动放大作用的方向相关性分析。研究结果表明，常用的矢量合成法分析结果与多向谱比上包络曲线法分析结果存在差异，前者存在忽略部分峰值的可能；多向谱比的极坐标等高线图可较直观地体现场地对地震动放大作用的方向相关性特征，但不同多向谱比表现存在差异；多向谱比峰值方向分布概率可较好地定量分析放大作用峰值在不同方向上的差异，但不同地震事件存在差异，不同的多向谱比存在差异。可采用多向谱比上包络曲线法分析场地放大作用，除可避免矢量合成法引起的误估外，也可更好地分析实际场地频率-方向相关的放大作用。

Study on Azimuth-related Site Amplification Effect of Seismic Ground Motion

In recent analysis on site amplification effect of seismic ground motion, the square root of HVSR and SBSR obtained from seismic observation in orthogonal direction was often used to characterize the site amplification effect, however, the azimuth-related site amplification effect of seismic ground motion is not considered. To discuss this effect, the azimuth-related HVSRs, SBSRs, and distribution probability of peak values on the spectral ratios were selected, and the surface and borehole seismic records on Xiangtang Array site in 11 earthquake events were collected, finally, the azimuth-related site amplification effect was analyzed. The results show: (1) the results from the square root algorithm have the risk of ignoring some frequencies which are different with the proposed upper envelope algorithm in this work, (2) the contour of azimuth-related spectral ratios in polar coordinates could directly represent the directionality characteristics of site amplification effect, but the results from different multi-directional spectral ratios are different, (3) the azimuth-related of peak values could characterize in quantity the difference in azimuth of site amplification effect, but the probabilities were various with the different multi-directional spectral ratio and the data from different event. According to the results and discussion in this work, the azimuth-related spectral ratios could be used in the analysis of site amplification effect, for avoiding the under-estimate of amplification effect by the square root algorithm, and the method could be used to understand the frequency-direction correlation of site amplification effect better.