王继鑫, 荣棉水, 李小军, 喻烟. 2020: 确定场地土层速度结构的改进半波长法. 地震学报, 42(3): 362-376. DOI: 10.11939/jass.20190142
引用本文: 王继鑫, 荣棉水, 李小军, 喻烟. 2020: 确定场地土层速度结构的改进半波长法. 地震学报, 42(3): 362-376. DOI: 10.11939/jass.20190142
Wang Jixin, Rong Mianshui, Li Xiaojun, Yu Yan. 2020: Improved half-wavelength method for determining the velocity structure of site soil layer. Acta Seismologica Sinica, 42(3): 362-376. DOI: 10.11939/jass.20190142
Citation: Wang Jixin, Rong Mianshui, Li Xiaojun, Yu Yan. 2020: Improved half-wavelength method for determining the velocity structure of site soil layer. Acta Seismologica Sinica, 42(3): 362-376. DOI: 10.11939/jass.20190142

确定场地土层速度结构的改进半波长法

Improved half-wavelength method for determining the velocity structure of site soil layer

  • 摘要: 地球物理反演浅地表土层波速剖面通常基于初始速度结构模型,为避免对地勘资料产生较多依赖,充分利用地震和背景噪声等被动源观测记录,快速简便地构建出土层反演的初始模型,本文基于场地土层的频散曲线和水平与竖向谱比提出了一种改进半波长法。该方法首先通过水平与竖向谱比确定场地土层的卓越频率,获取场地覆盖层厚度,确定反演所需的频带范围;其次,利用瑞雷波相速度对剪切波速的偏导数随土层深度的变化规律反演出场地的初始速度结构,并结合工程场地勘探中的半波长法,对常见的三类典型土层模型和日本Kushiro场地实测模型进行了实例分析;最后,将反演得到的速度结构与理论或实测速度结构进行误差对比分析。结果表明:改进半波长法获得的初始速度结构相对于理论或实测速度结构的最大误差不超过35%,可为利用地球物理方法反演工程场地波速剖面构造一个较小的搜索模型空间,进而提高反演计算的速度和结果的可靠性。

     

    Abstract: The initial velocity structure model is generally necessary in the study of geophysical inversion for shallow surface soil wave velocity profile. In order to avoid excessive reliance on the surveying data instead, and to make full use of observation records of passive sources such as earthquakes and ambient noise to quickly and easily construct the initial model of soil inversion, this paper proposes an improved half-wavelength method based on the dispersion curve and the horizontal-to-vertical spectral ratio (HVSR) of the soil layer. Firstly, the method deter-mines the predominant frequency of the soil layer by HVSR, and then obtains the depth of overlying soil, and determines the frequency band range required for the inversion. Next, invert initial velocity structure of the site by using the variation of the partial derivative of the Rayleigh wave velocity to the shear wave velocity with the depth of the soil layer. Combined with the half-wavelength method in engineering site exploration, three types of soil layer models frequently encountered and the measured model of Kushiro site in Japan were analyzed, and the error analysis of the velocity structure was carried out and compared with the theoretical or measured velocity structures. The research shows that the initial velocity structure obtained by the improved half-wavelength method has a maximum error not more than 35%, which can be used to reconstruct a small searching model space in inversion for the wave velocity profile of engineering site by using the geophysical method, so as to improve the speed of inversion calculations and the reliability of result.

     

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