含覆盖层峡谷地形对平面P、SV波的宽频散射模拟

含覆盖层峡谷对地震波的高频散射规律尚不明确．本文采用间接边界元方法(IBEM)分析半空间中含覆盖层峡谷地形对地震波的二维宽频散射，对入射波型、入射角度和频率、覆盖层深宽比等因素对覆盖层地震响应规律的影响进行探讨分析．结果表明：IBEM可高效精确地对地震波的散射进行宽频模拟．对中低频段（无量纲频率η10.0），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．另外，覆盖层形状和入射角度对地震波聚焦特征也具有重要影响，不同波型入射下聚焦区域有很大差别．实际含覆盖层峡谷地形地震反应分析需精细考虑波型、入射波频率和角度、覆盖层深宽比等因素，以更科学地进行震害解释和地震安全性评价．

Wide-Band Scattering Simulation of Plane P,SV Wave for Canyon Site Bearing a Covering Layer

The high frequency scattering law of seismic waves in layer covered canyon has not been identified. In this paper, the IBEM method is used to analyze the two dimensional broadband scattering of seismic wave in the canyon with a covering layer in Half Space. Analyses are made to investigate the influence of the wave type, incident frequency and angle, overburden depth-width ratio, and other factors on the overburden seismic response pattern. The numerical results demonstrate that the IBEM is effective and accurate in the simulation of seismic wave broadband scattering. In low and medium frequencies (dimensionless frequency η10.0) and even turns to the necking effect. As the covering layer depth increases, the bandwidth of the displacement amplification frequency gradually decreases, with a decreasing frequency at the first peak, and a stronger oscillation of spectrum curve in the low frequency. In addition, the shape of covering layer and the incidence angle have significant influences on the focusing characteristic of seismic wave, with significantly different focal regions for different wave incidences. The seismic response analysis of an actual layer covered canyon should carefully take into account the wave type, incident frequency and angle as well as the depth-to-width ratio of the covering layer so as to provide a more reasonable earthquake damage interpretation and seismic safety evaluation.