邻近山体地形地震动力相互作用边界元法模拟

Boundary element method simulation for seismic dynamic interaction of adjacent mountain terrain

采用动力间接边界元法,研究了平面P波、SV波入射时多个邻近山体之间的动力相互作用及地震动放大效应。结果表明:连绵多山地形的地震反应规律相比孤立山丘情况更为复杂;反应特征受控于入射波频率、角度、山体间距等因素,邻近山体对地震动放大或缩幅程度主要取决于其边缘激发面波的强度、相位及与观察点的距离。一般来说,当山体处于邻近山体对地震波散射形成的位移放大区域内,相比单山情况地震动会表现出增强放大效应,特定频段主方向反应可达到单山放大效应的约1.5倍。另需注意由于散射波的相干效应,两山之间平坦地表也表现出明显的放大效应。而高频波入射下,邻近山体相互作用效应明显减弱。实际复杂多山地形地震动评估需准确掌握输入地震波特性和连绵山体的材料、几何特征。

A new method of fundamental solution based on the dynamic indirect boundary element(IBEM) is proposed to study the dynamic interaction and amplification effect of ground motion between adjacent mountains for incident P waves and SV waves. Results obtained show that the seismic response of the mountainous terrain is more complicated than that of the isolated hills. The reaction characteristics are affected by the factors such as the frequency, angle of the incident waves and mountain distance. The degree of magnification or shrinkage of the ground motion caused by the nearby mountain is mainly determined by the edge of the excitation surface wave intensity, phase and distance from the observation point. Generally speaking, when the mountain is located in the displacement amplification area affected by the adjacent mountain, compared to the single mountain, the ground motion shows an enhanced amplification effect, up to 1.5 times than the single mountain amplification effect within some frequency ranges. It should also be noted that due to the coherence effect of the scattered waves, the flat ground surface between the two mountains also shows a significant amplification effect with amplitude up to 1.9 times than that of the free field at some frequeicies. Meanwhile, the interaction effect of adjacent mountain is obviously weakened by high frequency wave incidence. The actual complex mountainous terrain seismic assessment should accurately depend on the characteristics of the input seismic wave and the material and geometric characteristics of the continuous mountains.