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首页> 外文期刊>Bulletin of earthquake engineering >Alternative interpretations of horizontal to vertical spectral ratios of ambient vibrations: new insights from theoretical modeling
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Alternative interpretations of horizontal to vertical spectral ratios of ambient vibrations: new insights from theoretical modeling

机译：环境振动的水平到垂直频谱比的替代解释：理论建模的新见解

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Different positions exist about the physical interpretation of horizontal to vertical spectral ratios (HVSR) deduced from ambient vibrations. Two of them are considered here: one is based on the hypothesis that HVSR are mainly conditioned by body waves approaching vertically the free surface, the other one assumes that they are determined by surface waves (Rayleigh and Love, with relevant upper modes) only. These interpretations can be seen as useful approximations of the actual physical process, whose reliability should be checked case-by-case. To this purpose, a general model has been here developed where ambient vibrations are assumed to be the complete wave field generated by a random distribution of independent harmonic point sources acting at the surface of a flat stratified visco-elastic Earth. Performances of the approximate interpretations and complete wave field models have been evaluated by considering a simple theoretical subsoil configuration and an experimental setting where measured HVSR values were available. These analyses indicate that, at least as concerns the subsoil configurations here considered, the surface-waves approximation seems to produce reliable results for frequencies larger than the fundamental resonance frequency of the sedimentary layer. On the other hand, the body waves interpretation provides better results around the resonance frequency. It has been also demonstrated that the HVSR curve is sensitive to the presence of a source-free area around the receiver and that most energetic contribution of the body waves component comes from such local sources. This dependence from the sources distribution implies that, due to possible variations in human activities in the area where ambient vibrations are carried on, significant variations are expected to affect the experimental HVSR curve. Such variations, anyway, only weakly affect the location of HVSR maximum that confirms to be a robust indicator (in the range of 10%) of the local fundamental resonance frequency.
机译：关于从环境振动推导出的水平频谱比与垂直频谱比（HVSR）的物理解释，存在着不同的立场。这里考虑其中的两种：一种基于以下假设：HVSR主要由垂直接近自由表面的体波决定，另一种假设它们仅由表面波（瑞利和洛夫，具有相关的上模）确定。这些解释可以看作是实际物理过程的有用近似，应逐案检查其可靠性。为此，在此开发了一个通用模型，其中假定环境振动是由作用在平坦的层状粘弹性地球表面的独立谐波点源的随机分布产生的完整波场。通过考虑简单的理论下土层配置和可测量HVSR值的实验设置，评估了近似解释和完整波场模型的性能。这些分析表明，至少就此处考虑的地下土壤构造而言，对于大于沉积层基本共振频率的频率，表面波近似似乎产生了可靠的结果。另一方面，体波解释在共振频率附近提供了更好的结果。还已经证明，HVSR曲线对接收器周围无源区域的存在很敏感，并且体波分量的最有力贡献来自这种局部源。来自源分布的这种依赖性意味着，由于在进行环境振动的区域中人类活动的可能变化，预计会有很大变化影响实验HVSR曲线。无论如何，这样的变化仅会微弱地影响HVSR最大值的位置，从而确定是本地基本谐振频率的可靠指标（在10％的范围内）。

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