Empirical transfer functions (ETFs) between seismic records observed at the surface and depth represent a powerful tool to estimate site effects for earthquake hazard analysis. However, conventional modeling of site amplification, with assumptions of horizontally polarized shear waves propagating vertically through 1D layered homogeneous media, often poorly predicts the ETFs, particularly, in which large lateral variations of velocity are present. Here, we test whether more accurate site effects can be obtained from theoretical transfer functions (TTFs) extracted from physics‐based simulations that naturally incorporate the complex material properties. We select two well‐documented downhole sites (the KiK‐net site TKCH05 in Japan and the Garner Valley site, Garner Valley Downhole Array, in southern California) for our study. The 3D subsurface geometry at the two sites is estimated by means of the surface topography near the sites and information from the shear‐wave profiles obtained from borehole logs. By comparing the TTFs to ETFs at the selected sites, we show how simulations using the calibrated 3D models can significantly improve site amplification estimates as compared to 1D model predictions. The primary reason for this improvement in 3D models is redirection of scattering from vertically propagating to more realistic obliquely propagating waves, which alleviates artificial amplification at nodes in the vertical‐incidence response of corresponding 1D approximations, resulting in improvement of site effect estimation. The results demonstrate the importance of reliable calibration of subsurface structure and material properties in site response studies.

中文翻译：

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具有 3D 速度结构的经验传递函数建模

在地表和深度观测到的地震记录之间的经验传递函数 (ETF) 代表了一种强大的工具，可以估计地震危害分析的场地效应。然而，场地放大的传统建模，假设水平极化横波通过一维分层均匀介质垂直传播，通常不能很好地预测 ETF，特别是在存在较大横向速度变化的情况下。在这里，我们测试是否可以从基于物理的模拟中提取的理论传递函数 (TTF) 中获得更准确的场地效应，这些模拟自然地结合了复杂的材料特性。我们选择了两个有据可查的井下站点（日本的 KiK-net 站点 TKCH05 和加利福尼亚州南部的 Garner Valley 站点，Garner Valley Downhole Array）进行研究。两个站点的 3D 地下几何形状是通过站点附近的地表地形和从钻孔测井获得的横波剖面信息来估计的。通过比较选定站点的 TTF 与 ETF，我们展示了与 1D 模型预测相比，使用校准的 3D 模型的模拟如何显着改善站点放大估计。3D 模型中这种改进的主要原因是将散射从垂直传播重定向到更真实的倾斜传播波，这减轻了相应 1D 近似值的垂直入射响应中节点处的人工放大，从而改进了场地效应估计。结果证明了在场地响应研究中对地下结构和材料特性进行可靠校准的重要性。