SUMMARY The promise of passive seismology has increasingly been realized in recent years. Given the expense in installing and maintaining seismic station networks, it is important to extract as much information from the measurements as possible. In this context, the ellipticity or H/V amplitude ratio of Rayleigh waves can prove to be a valuable observable in ambient noise seismology due to its complimentary sensitivity to subsurface structure, compared to phase and group-velocity dispersion, as well as its potential for constraining VP structure in addition to VS. However, the suitability of the Rayleigh H/V ratio in noise-based studies depends on the accurate interpretation of measurements made on multicomponent ambient-noise cross-correlations. We present a synthetic study that critically examines measurements commonly interpreted as the Rayleigh-wave H/V ratio, under realistic scenarios of spatially distributed and non-uniform noise sources. Using the surface wave terms of Green’s function in a laterally homogeneous medium, we rigorously model multicomponent cross-correlations for arbitrary noise-source distributions and extract from them standard estimates of the H/V ratio. Variation of these measurements as a function of VP is studied empirically, by brute-force simulation. We find that the measurements depart significantly from the theoretical Rayleigh-wave H/V for the medium in question, when noise sources are strongly directional or anisotropic. Love waves, if present in the cross-correlations, also have the potential to significantly bias interpretation. Accurate interpretation of the H/V ratio measurement thus rests on carefully modelling these effects. However, the sensitivity to VP structure is comparable to that of the classic Rayleigh-wave H/V. We also propose a new measurement for cross-correlations that has slightly greater sensitivity to VP. Finally, uncertainty analysis on synthetic tests suggests that simplistic interpretations of Rayleigh-wave ellipticity are only effective (in resolving VP structure) when the Love-wave contamination is negligible and measurement uncertainties are less than 10 per cent.

中文翻译：

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基于环境噪声互相关的瑞利波 H/V 比测量及其对 VP 的敏感性：一项数值研究

小结 近年来，被动地震学的希望越来越多地实现。鉴于安装和维护地震台站网络的费用，从测量中提取尽可能多的信息非常重要。在这种情况下，与相位和群速度色散相比，瑞利波的椭圆率或 H/V 幅度比可以证明是环境噪声地震学中的一个有价值的观测值，因为它对地下结构的互补敏感性，以及它的潜力除 VS 外，约束 VP 结构。然而，瑞利 H/V 比在基于噪声的研究中的适用性取决于对多分量环境噪声互相关测量值的准确解释。我们提出了一项综合研究，该研究在空间分布和非均匀噪声源的现实场景下，批判性地检查通常解释为瑞利波 H/V 比的测量值。使用横向均匀介质中格林函数的表面波项，我们对任意噪声源分布的多分量互相关进行严格建模，并从中提取 H/V 比的标准估计值。这些测量值的变化作为 VP 的函数是通过蛮力模拟凭经验研究的。我们发现，当噪声源具有很强的方向性或各向异性时，测量值明显偏离了所讨论介质的理论瑞利波 H/V。爱波，如果存在于互相关中，也有可能显着偏向解释。因此，对 H/V 比率测量的准确解释取决于对这些影响的仔细建模。然而，对 VP 结构的敏感性与经典的瑞利波 H/V 相当。我们还提出了一种新的互相关测量方法，它对 VP 的敏感性略高。最后，综合测试的不确定性分析表明，瑞利波椭圆率的简单解释仅在洛夫波污染可忽略不计且测量不确定性小于 10% 时才有效（在解析 VP 结构中）。