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为估计二维横向不均匀、非弹性介质的地面运动,将振型叠加法和有限差分方法相结合,发展了一种复合技术,无论震源距大小,都可以计算地震形成的局部波场,它可考虑震源、路径和局部场地土的影响。作为实际应用,我们模拟了由1985年9月19日米却肯地震形成的墨西哥城的地震动。研究墨西哥城双层沉积地层的一维地震反应,可解释湖床区内、外接收记录的地震波振幅之差异。那些简单模型显示,沉积盖层使得地震动水平分量高频波(0.2～0.5Hz)增多。湖床区内观测地面运动的大振幅的尾波以及湖床区内、外观测信号的频谱比率只能用沉积盆地的二维模型解释,在这种模型中,地面运动主要受最上部粘土层地震反应的控制。合成地震波体现了观测到的地面运动的主要特征(相对振幅、频谱比率、频率成分)。湖床区内观测的地面运动大振幅的尾波可解释为共振以及横向不均匀粘土层激发的局部面波的影响。对1985年米却肯地震,在解释观测到的持续时间时三个子事件提供的能量是非常重要的。
In order to estimate the ground motion of non-elastic and transverse two-dimensional media, a combination technique is developed by combining the modal superposition method with the finite difference method. The composite wave field can be calculated regardless of the focal distance The effects of sources, paths and local site soil can be considered. As a practical application, we simulated ground motion in Mexico City, which was formed on September 19, 1985, by the Mitochond earthquake. A study of the one-dimensional seismic response of a double-layer sedimentary formation in Mexico City can explain the differences in the amplitudes of seismic waves received and recorded within and outside the lake bed. Those simple models show that the sedimentary cover increases the high-frequency (0.2-0.5 Hz) horizontal component of ground motion. The large-amplitude coda waves observed in the lake bed area and the spectral ratios of the observed signals inside and outside the lake bed can only be explained by the two-dimensional model of the sedimentary basin. In this model, the ground motion is mainly affected by the uppermost clay layer Seismic response control. Synthetic seismic waves reflect the main features of observed ground motion (relative amplitude, spectral ratio, frequency content). The large-amplitude coda waves of the ground motion observed in the lake bed region can be explained by the effects of resonance and local surface waves excited by the laterally inhomogeneous clay layer. For the 1985 Michoacan earthquake, the energy provided by the three sub-events is very important in explaining the observed duration.