基于地震观测记录的场地竖向非线性性质

    Investigating Vertical Nonlinearity of Site Using KiK-net Seismic Data

    • 摘要: 为了解决基于地震观测记录的场地竖向非线性性质评估的问题,基于日本基岩强震观测网(Kiban-Kyoshin strong motion observation network,KiK-net)地震观测记录,以场地压缩模量与压缩波速为代表分别从压缩模量曲线、竖向非线性阈值以及竖向性质恢复过程三方面探究场地的竖向非线性性质.首先使用地震干涉测量法与土动力参数法从地震观测记录中提取场地的动力参数,然后结合目前已有的场地压缩模量衰减模型估计场地的压缩模量曲线并开展相关研究.此外,通过引入时频分析技术增加强震记录的数目并进一步验证相关场地压缩模量衰减模型的有效性.主要结果如下:1)与水平非线性阈值相比,场地竖向非线性阈值整体上更大,且离散性更高,其阈值应变范围为10-6~10-4.2)场地压缩波速受强震影响的最大下降幅度明显小于剪切波速,针对2011年东日本大地震,两者最大下降幅度差距在10%~15%;与最大下降幅度相比,场地压缩波速与剪切波速在强震作用之后的恢复过程并无明显规律性的区别.3)场地压缩模量曲线衰减下限与围压以及地下水位均呈负相关关系.研究基于地震观测记录评估了场地的竖向非线性性质,并从地震观测角度证明地下水对场地竖向非线性性质的抑制作用.

       

      Abstract: The importance of the vertical nonlinearity of site on the earthquake response analysis has been addressed by many researchers. However, most of the related studies have focused on the horizontal ground motion, while the knowledge of the vertical nonlinearity is limited. To investigate the vertical nonlinearity of site, including the modulus degradation curve, nonlinear threshold and recovery process, the constrained modulus and compression wave velocity were estimated based on the KiK-net (Kiban-Kyoshin strong motion observation network) seismic data in this study. First, dynamic parameters of sites were extracted by seismic interferometry and soil dynamic parameter technique. Then in-situ constrained modulus degradation curves were estimated based on a currently available model. Furthermore, time-frequency analysis was used to obtain more strong motion records, hence the constrained modulus degradation model can be further verified. Main results are as follows: 1) On the whole, the nonlinear threshold of vertical ground motion is larger and has a wider range (10-6-10-4) compared with that of horizontal ground motion. 2) The recovery process of the vertical behavior of site is basically consistent with that of the horizontal behavior and the influence of strong earthquake on the compression wave velocity is obviously less than that on the shear wave velocity, e.g., 10%-15% difference for Tohoku-Oki earthquake. 3) The lower limit of the in-situ constrained modulus degradation curve is negative correlated with groundwater table and confine pressure. In-situ vertical nonlinearity is evaluated based on seismic data in this study and the results can be regarded as the verification of the inhibiting effect of the groundwater on the vertical nonlinearity of site.

       

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