二维模型与三维模型地震动地形效应差异性研究

Difference of ground motion topographic effect between 2D model and 3D model

  • 摘要: 将三维模型简化为二维模型进行分析是一种提升计算效率的方法,但与实际情况存在一定偏差,特别是在复杂地形条件下,忽略面外地形特征可能会对二维分析结果产生较大影响。本文旨在探讨二维模型与三维模型地震动分析的差异性。以磨西台地区域地形为依据分别建立二维截面模型与三维区域模型,并对该区域地形的地震响应进行分析。将二维模型与三维模型的地表地震动放大系数(GMAF)分布及加速度频谱曲线进行对比,获得二者的差异性。探讨地震波不同入射方位下地表地震动的变化规律。研究结果表明:对于三维模型,地震波会因复杂地形表面多次反射,而产生入射波面外方向较为明显的震动现象,但二维模型易忽略这一现象;地震波从不同方位入射会改变地表面内坡度和面外坡度的取值,从而影响地震波的反射和散射规律,导致各点震动幅度发生变化。若忽视这一因素,可能难以准确评估复杂地表运动情况。

     

    Abstract: Simplifying the 3D model into a 2D model for analysis is a method to improve the computational efficiency, but there is a certain deviation from the actual situation, especially in the complex terrain conditions, ignoring the out-of-plane terrain features may have a great impact on the 2D analysis results.This paper aims to discuss the difference of ground motion analysis between 2D model and 3D model. A 2D cross-section model and a 3D regional model are established based on the terrain of Moxi Platform, and the seismic response of the terrain in this region is analyzed. The surface GMAF distribution and acceleration spectrum curves of 2D model and 3D model are compared to obtain the difference between them. The variation law of ground motion under different incidence orientations of seismic waves is discussed. The results show that: for the 3D model, the seismic wave will be reflected by the surface of the complex terrain for many times, and the incident wave will cause a more obvious vibration phenomenon in outward direction, but the 2D model is easy to ignore this phenomenon. The seismic wave incident from different directions will change the values of in plane slope and out-of-plane slope of the ground surface, which will affect the reflection and scattering law of the seismic wave, and lead to the change of the vibration amplitude of each point. If this factor is ignored, it may be difficult to accurately assess the complex ground motions.

     

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