含松软覆盖层V型峡谷对Rayleigh波的宽频散射

Broadband scattering of Rayleigh waves by a V-shaped canyon with soft covering layer

含松软覆盖层峡谷地形对地震动具有放大效应已被多次地震观测所证实。本文对Rayleigh波入射下V形覆盖层峡谷的地震反应进行宽频模拟,讨论了V形峡谷深度、覆盖层软硬程度、倾角以及波的频率等因素对地表位移幅值的影响。数值结果表明:在中低频段(量纲为一的频率η<5.0),含覆盖层峡谷地形对地震波的放大效应显著。在高频波段(η>10.0),覆盖层放大效应减弱甚至出现缩幅效应;随覆盖层深度增加,位移放大频段的带宽逐渐减小,第一峰值频率降低,且在低频段频谱曲线振荡剧烈;覆盖层越软,位移越大,峡谷表面位移空间变化越剧烈;峡谷右边界与水平面夹角不同,导致地表位移幅值的空间分布相差较大,在中低频时峡谷右侧的图线差异比较明显,在高频时变化差异不大。由此可见覆盖层软硬程度和形状对地震波聚焦特征也具有重要影响。

The amplification effect of the canyon with soft covering layer on the ground motion has been confirmed by many seismic observations. In this paper, the seismic response of the V-shaped cover canyon on broadband of incident Rayleigh wave is simulated. Influences of the depth of V-shape canyon, the hardness of cover layer, dip angle of canyon and frequency of incident wave on the surface displacement amplitude are discussed. Numerical results obtained show that the amplification effect of the canyon on the seismic wave is significant on mid and low-frequency band(non-dimensional frequency η less than 5.0). On the high-frequency band(non-dimensional frequency η greater than 10.0), the amplification effect of the cover layer decreases and even shrinks. With the increase of coverage depth, the bandwidth of the displacement amplifying frequency band decreases, the first peak frequency decreases, and the frequency spectrum curve oscillates violently at low frequency. In addition, the hardness of cover layer and dip angle of canyon have important influence on the seismic wave focusing characteristics.