Theories related to the Earth's attenuation effect and earthquake source properties predict a similar spectral falloff of body waves, creating severe trade-off problems when determining these two processes from waveform spectra. Previous efforts attempted to suppress this trade-off by either applying an empirical Green's function or conducting linear inversion with a specially designed event–station configuration. However, both approaches encounter difficulties when dealing with large datasets or site effect contamination. In this study, we modify a previously used cluster-event method (CEM), combining both the spectral amplitude and the spectral ratio of the P-waves for the clustering of events (CEM2); we then apply CEM2 to the High-Sensitivity Seismograph Network data in the Tohoku region of Japan. An initial inversion with CEM2 yields the first estimates of the source and path parameters, that is, the corner frequency (f_c) and the quality factor (Q). The residuals of this inversion demonstrate distinct spectral characteristics that are well correlated with vertical-to-horizontal (V/H) spectral ratios of the P-coda waves at each station, suggesting that they represent a form of site response unaccounted for by theoretical predictions of Q and f_c. After removing this particular site response, the second inversion yields an improved determination of Q. We hypothesize that this site effect is dominated by P to SV conversion upon P-wave arrival and develops and amplifies toward the coda waves. Furthermore, the site effect demonstrates systematic regional characteristics, some of which correlate well with those derived from the V/H spectral ratios of the P-coda waves.

中文翻译：

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从 P 波光谱中提取站点效应：簇事件方法 2 （CEM2） 在日本东北地区的应用


与地球衰减效应和地震源特性相关的理论预测了体波的类似频谱衰减，因此在从波形频谱确定这两个过程时会产生严重的权衡问题。以前的努力试图通过应用经验格林函数或使用专门设计的事件站配置进行线性反演来抑制这种权衡。然而，在处理大型数据集或位点效应污染时，这两种方法都遇到了困难。在这项研究中，我们修改了以前使用的聚类事件方法 （CEM），结合了 P 波的光谱幅度和光谱比，用于事件聚类 （CEM2）;然后，我们将 CEM2 应用于日本东北地区的高灵敏度地震仪网络数据。使用 CEM2 进行初始反演会产生源和路径参数的初步估计值，即转折频率 （f _c ） 和品质因数 （Q）。这种反转的残差表现出不同的频谱特性，这些特性与每个站点的 P-coda 波的垂直与水平 （V/H） 光谱比密切相关，表明它们代表了一种 Q 和 f _c 的理论预测未解释的站点响应形式。删除此特定站点响应后，第二次反转可改进 Q 的测定。我们假设这种位点效应在 P 波到达时以 P 到 SV 的转换为主，并向尾波发展和放大。此外，站点效应表现出系统的区域特征，其中一些特征与 P-coda 波的 V/H 光谱比得出的特征密切相关。