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Empirical evaluation of microtremor H/V spectral ratio

机译：小震H / V光谱比的实证评估

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The objective of this work is to perform a purely empirical assessment of the actual capabilities of the horizontal-to-vertical (H/V) spectral ratio technique to provide reliable and relevant information concerning site conditions and/or site amplification. This objective has been tackled through the homogeneous (re)processing of a large volume of earthquakes and ambient noise data recorded by different research teams in more than 200 sites located mainly in Europe, but also in the Caribbean and in Tehran. The original recordings were first gathered in a specific database with information on both the sites and recorded events. Then, for all sites close to an instrumented reference, average site-to-reference spectral ratios ("spectral ratio method" (SSR)) were derived in a homogeneous way (window selection, smoothing, signal-to-noise ratio threshold, averaging), as well as H/V ratios ("HVSRE-RF") on earthquake recordings. H/V ratios were also obtained from noise recordings at each site (either specific measurements, or extracted from pre- or post-event noise windows). The spectral curves resulting from these three techniques were estimated reliable for a subset of 104 sites, and were thus compared in terms of fundamental frequency, amplitude and amplification bandwidth, exhibiting agreements and disagreements, for which interpretations are looked for in relation with characteristics of site conditions. The first important result consists in the very good agreement between fundamental frequencies obtained with either technique, observed for 81% of the analyzed sites. A significant part of the disagreements correspond to thick, low frequency, continental sites where natural noise level is often very low and H/V noise ratios do not exhibit any clear peak. The second important result is the absence of correlation between H/V peak amplitude and the actual site amplification measured on site-to-reference spectral ratios. There are, however, two statistically significant results about the amplitude of the H/V curve: the peak amplitude may be considered as a lower bound estimate of the actual amplification indicated by SSR (it is smaller for 79% of the 104 investigated sites), and, from another point of view, the difference in amplitude exhibits a questioning correlation with the geometrical characteristics of the sediment/basement interface: large SSR/HV differences might thus help to detect the existence of significant 2D or 3D effects.
机译：这项工作的目的是对水平/垂直（H / V）光谱比技术的实际能力进行纯粹的经验评估，以提供有关工位条件和/或工位放大的可靠且相关的信息。通过对主要在欧洲，以及在加勒比海和德黑兰的200多个地点的不同研究小组记录的大量地震和环境噪声数据进行均质（重新）处理，解决了该目标。首先将原始录音收集到一个特定的数据库中，其中包含有关站点和已记录事件的信息。然后，对于所有接近仪器参考的站点，以均一的方式（窗口选择，平滑，信噪比阈值，平均）得出平均站点与参考的光谱比（“光谱比法”（SSR）） ），以及地震记录中的H / V比（“ HVSRE-RF”）。还可以从每个站点的噪音记录中获得H / V比率（特定的测量结果，或者从事前或事后的噪音窗口中提取）。据估计，这三种技术产生的光谱曲线对于104个站点的子集是可靠的，因此在基本频率，幅度和放大带宽，表现出一致性和分歧方面进行了比较，并寻求与站点特征相关的解释条件。第一个重要结果是，用两种技术获得的基本频率之间都具有很好的一致性，对于81％的分析位点都可以观察到。分歧的很大一部分对应于大陆频率低，自然噪声水平通常很低且H / V噪声比没有任何清晰峰值的大陆地区。第二个重要结果是，H / V峰值幅度与以位点与参考光谱之比测量的实际位点放大率之间没有相关性。但是，关于H / V曲线的幅度有两个统计上显着的结果：峰值幅度可以看作是SSR指示的实际扩增的下限估计（对于104个研究位点中的79％较小）并且，从另一个角度来看，振幅的差异与沉积物/基底界面的几何特征呈现出令人怀疑的相关性：较大的SSR / HV差异可能因此有助于检测是否存在明显的2D或3D效应。

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