Quarter-wavelength (QWL) velocity refers to the S-wave velocity at a depth equal to one-fourth of the wavelength of the seismic waves. It provides valuable information about the characteristics of the subsurface material properties affecting seismic waves propagation. The Swiss Seismological Service (SED) network, with over 200 stations across different lithologies, offers a rich dataset to implement correlation between site properties and site amplification factors. The current study is based on a subset of 113 selected SED seismic stations for which shear-wave velocity (Vs) profiles from geophysical measurements are available. We first meticulously analyzed and adjusted them to accurately determine the bedrock depth of the sites they are located on. Using empirical spectral modelling (ESM), we computed amplification functions from recorded earthquakes, referenced to the Swiss standard rock profile with a V of 1100 m/s. Then we performed a bivariate analysis between empirical amplification functions, QWL velocity and QWL velocity contrast. The resulting coefficients are used to predict elastic amplification at frequencies between 0.5 and 10 Hz, with predictions generally being within 20–28% of observed values. We also developed an empirical equation relating V (time-averaged Vs to 30 m depth) and κ (high-frequency attenuation parameter), to incorporate the anelastic term in the amplification. Applying our method to a 3D geophysical model of Visp, a high seismic hazard zone in Switzerland, we found it effective in predicting 1D site amplification, but noted caution in areas susceptible of 2D/3D resonance effects. A calibration function based on observed vs. predicted amplification and the frequencies of estimation normalized by the expected 2D resonance frequency improved predictions for Visp. Our study demonstrates that QWL velocity profiles offer a straightforward approach for characterizing site effects, which can be used in seismic hazard assessment to evaluate the potential amplification of ground motions.

中文翻译：

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从四分之一波长速度剖面估计位点特异性放大函数及其在获得局部放大图方面的应用


四分之一波长（QWL）速度是指深度等于地震波波长四分之一的横波速度。它提供了有关影响地震波传播的地下材料特性的宝贵信息。瑞士地震局 (SED) 网络拥有 200 多个跨越不同岩性的台站，提供丰富的数据集来实现场地属性和场地放大系数之间的关联。当前的研究基于 113 个选定的 SED 地震台的子集，这些地震台的地球物理测量的剪切波速度 (Vs) 剖面可用。我们首先对它们进行了细致的分析和调整，以准确确定它们所在地点的基岩深度。我们使用经验谱模型 (ESM)，参考 V 为 1100 m/s 的瑞士标准岩石剖面，计算了记录的地震的放大函数。然后我们在经验放大函数、QWL 速度和 QWL 速度对比之间进行双变量分析。所得系数用于预测 0.5 至 10 Hz 频率下的弹性放大，预测值通常在观测值的 20-28% 范围内。我们还开发了一个与 V（30 m 深度的时间平均 V）和 κ（高频衰减参数）相关的经验方程，以将滞弹性项纳入放大中。将我们的方法应用于瑞士高地震危险区 Visp 的 3D 地球物理模型，我们发现它可以有效预测 1D 站点放大，但在易受 2D/3D 共振效应影响的区域中要小心。基于观测值与实际值的校准函数 预测的放大率和通过预期 2D 共振频率归一化的估计频率改进了 Visp 的预测。我们的研究表明，QWL 速度剖面提供了一种描述场地效应的直接方法，可用于地震危险评估，以评估地面运动的潜在放大程度。