自贡西山公园山脊场地地形和土层效应数值模拟

Numerical Simulation for Site Effect of Ridge Terrain and Overlaying Soil in Zigong Xishan Park

利用自贡地形影响强震动观测台阵在汶川地震中获得的强震动记录,以位于山脚下基岩上的台站为参考点,采用传统谱比法对场地放大效应进行了初步分析;同时用显式有限元-有限差分方法模拟了自贡西山公园山脊场地地形和土层的地震动效应,并进行了数值模拟结果与强震动观测结果的对比分析。结果表明:上覆土层对地震动的放大作用相对于地形变化的放大作用更为明显;地形对地震动水平分量的放大效应要明显于对竖直分量的放大效应;采用二维模型对上覆土层的模拟与观测结果较吻合,对于基岩介质部分的模拟在低频范围内也能反映山脊地形对地震动的影响。

Site amplification was analyzed for the ridge terrain of Zigong Xishan park using the strong motion record obtained in Wenchuan earthquake by traditional spectral ration method. The reference seismic station of spectral ration was located near the foot of the ridge. Ground motion response of the ridge terrain in Zigong Xishan park was simulated by the explicit finite element-finite difference method. The results of numerical simulation were compared with the observed values of strong motion records, which shows that this numerical simulation model could reflect the ridge terrain basically. Numerical modeling results showed these conclusions as follows. Amplification action of the overlaying soil to seismic acceleration was more obvious than that of the topographic change. Horizontal component of the seismic ground motion was amplified by topography variation more evidently than vertical component. The two-dimensional model built in this paper could well simulate the ground motion on overlaying soil and the results coincided well with the observation results. Simulation for bedrock could reflect the ground motion response of the ridge terrain in low frequency range.