河谷场地地震波传播理论及散射规律研究

There are many important rivers in China. The economic growth requires a fully exploration of these river areas. A huge number of significant facilities such as high dams, long bridges have been constructed or planed in valleys or canyons. The seismic design of this kind of constructions located at irregular sites is of critical importance because China is also an earthquake-prone country. As a kind of irregular surface site, valleys play a major role in affecting the earthquake hazard distribution. Therefore, there is an urgent need for deeper investigation of the theory of seismic wave propagation and scattering. This study is to develop the classic method of wavefunction separation with the aid of domain decomposition strategies which take into account the stress singularities of real engineering sites. A series of analytic or semi-analytic solutions to wave motion problems are expected and can be used to reveal fundamental wave phenomena. These solutions to the scattering of seismic waves induced by alluvial valleys as well as empty canyons can 1) shed light on the relative role of soil amplification and topographic amplification effects; 2) reveal the influences of earthquake sources on the site effects; 3) explore the amplifications and spatial variations of the ground motion on the complicated engineering sites of valleys in order to provide a theoretical foundation for the spatial varying input of ground motions in huge constructions. Finally, the evaluation of earthquake ground motions within the sites of big projects is expected to be improved.

我国大江大河众多，近年来，由于经济发展的需要，各个流域都得到大规模的开发，我国在河谷场地已建、在建和拟建了许多大型的水坝、桥梁等重要基础设施工程。而我国又是一个多地震国家，这些大型工程的抗震问题极其重要。河谷作为一种局部不规则场地对震害分布影响很大，迫切需要开展河谷场地地震波传播理论及散射规律的研究。本项目基于波函数展开和区域分解策略，考虑实际河谷工程场地边角处的应力奇异特征，发展波动问题的解析或半解析方法，专注于揭示基本的波动现象，深入分析沉积河谷场地和无沉积的河谷地形对地震波的散射规律，探索地形效应和土层效应的相对重要性，研究震源对场地效应的影响，揭示复杂河谷工程场地引起的地面运动放大和空间变化规律，为大型工程科学合理的非一致地震动输入提供理论依据，进而有针对性地改进大型工程场地地震动场的评估方法。

河谷场地是一种常见的凹陷地形，且在河谷场地修建了大量工程（如土石坝、桥梁等）。实际震害调查表明地形及场地条件对地震灾害影响很大。针对河谷场地地震波传播解析模型与放大效应，取得了以下5个方面的创新成果：①基于时域调整的反应谱拟合方法，提出了一种改进的反应谱拟合的时域调整方法，来对地震动进行调整，使得其反应谱与规范反应谱相一致，克服了地震动速度、位移时程的零飘问题，且能够高效、高精度得满足拟合要求。②基于多点地震动条件模拟方法中的Kriging方法，提出了一个改进的多点地震动条件模拟方法，从而避免了该方法模拟的多点地震动的功率谱函数存在偏度误差。证明了改进方法所模拟的地震动的无偏性，并给出了该模拟方法得到的功率谱函数的随机误差的理论解答。③基于二维地震波的传播模型来考虑河谷场地地震波的地形效应，并假定河谷场地下任意两点的相干函数模型与平整场地条件下其在场地表面垂直投影的两点相干函数模型相同，提出了河谷地形中多点地震动的空间相关模型，在该模型中考虑了地震动的空间相关效应、行波效应以及河谷地形的地形效应。④用线源柱面SH波模拟入射地震波，构造了线源柱面SH波自由场，提出了线源柱面SH波作用下的半圆形沉积谷模型，将震源和场地联系了起来，揭示了震源位置对场地放大效应的影响规律。⑤场地效应通常包含土层放大效应和地形放大效应，为了揭示二者的相对贡献，构造了平面SH波作用下部分充填月牙形沉积谷的解析模型，得到了部分充填圆弧形沉积谷对平面SH波散射的波函数级数解，揭示了沉积物（覆盖层）对地震波的放大效应。