SUMMARY

Tien Shan of central Asia is known as one of the world's largest, youngest and most active intracontinental orogens. In this study, we implemented the horizontal-to-vertical spectral ratio (HVSR) technique as a widely used first-order approximation of the site effect parameters (i.e. fundamental frequency and site amplification). A set of data including 2119 strong-motion recordings from 468 earthquakes with hypocentral distances up to 500 km and small to moderate moment magnitudes ($ {M_{\rm{w}}}\sim $3.0–5.5) recorded by 24 broad-band stations from five different networks, located in Afghanistan, Tajikistan and Kyrgyzstan was deployed to investigate site-specific characteristics. We fitted a Gaussian-shape pulse function to evaluate fundamental frequencies and site amplifications. The HVSRs analysis revealed that although the majority of the stations (16 out of 24) show flat amplification functions, there are few stations with single sharp amplification functions. Then, we classified the stations based on the predominant frequency. Furthermore, we approximated the time-averaged shear wave velocity in the uppermost 30 m (${V_{{\rm{S}}30}}$) using the fundamental frequency and its corresponding amplitude. Moreover, we compared the HVSRs obtained from P waves, S waves, coda and pre-event noise. All peak frequencies including the fundamental frequency estimated from different seismic phases are in good agreement; whereas generally, the amplitude of the P-wave window is the lowest, the amplitudes of the S wave and noise windows are similar to the whole record and the amplitudes of early and late coda windows are the highest. We also observed that the HVSRs of noise using a 5 s window may have anomalous high amplitudes and peaks. These anomalous high amplitudes and peaks in the noise HVSRs indicate the existence of some unnatural sources or artefacts such as traffic and wind with specific resonance frequencies, suggesting 5 s ambient noise window is insufficient to capture site characteristics. Finally, to assess the reliability of the determined geotechnical results, we implemented a blind theoretical HVSR inversion to obtain representative shear wave velocity profiles as well as ${V_{{\rm{S}}30}}$ along with associated uncertainties for stations characterized by a single-peak HVSR curve using a Bayesian statistical framework.

中文翻译：

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研究水平-垂直分量频谱比率以替代中亚站点分类

概要

中亚天山被称为世界上最大，最年轻和最活跃的大陆内造山带之一。在这项研究中，我们将水平与垂直光谱之比（HVSR）技术用作站点效果参数（即基本频率和站点放大）的广泛使用的一阶近似。一组数据包括24个宽带记录的468次地震的2119次强震记录，震中距最远达500 km，矩矩小至中度（$ {M _ {\ rm {w}}} \ sim $ 3.0–5.5）部署了来自阿富汗，塔吉克斯坦和吉尔吉斯斯坦的五个不同网络的气象站，以调查特定地点的特征。我们安装了高斯形状的脉冲函数来评估基本频率和位点放大。HVSR分析显示，尽管大多数站点（24个站点中有16个）显示平坦的放大功能，但很少有具有单一尖锐放大功能的站点。然后，我们根据主要频率对电台进行分类。此外，我们使用基频及其相应的振幅近似了最上方30 m（$ {V _ {{\ rm {S}} 30}} $的时间平均剪切波速度。此外，我们比较了从P波，S波，尾声和事前噪声。所有峰值频​​率，包括从不同地震相位估计的基频，都吻合良好；而通常，P波窗口的幅度是最低的，S波的幅度是波浪和噪音窗口与整个记录相似，早期和晚期尾声窗口的幅度最高。我们还观察到，使用5 s窗口的噪声的HVSR可能具有异常的高振幅和峰值。HVSR噪声中的这些异常高振幅和峰值表明存在某些不自然的源或伪像，例如具有特定共振频率的交通和风，这表明5 s的环境噪声窗口不足以捕获站点特征。最后，为了评估确定的岩土结果的可靠性，我们实施了盲目理论HVSR反演，以获得代表性的剪切波速度剖面以及$ {V _ {{\ rm {S}} 30}} $以及站的相关不确定性使用贝叶斯统计框架的特征在于单峰HVSR曲线。