Seismic Ground Motion in Sedimentary Valleys: Focusing or Chaos?

9319339比拉克1985年墨西哥地震引起了人们的注意，即当强烈地面运动从基岩传播到上覆的沉积沉积时，其放大作用。在美国的主要城市，例如洛杉矶盆地，也可能存在类似的情况。这项研究计划的主要目的是通过计算机模拟，研究由基岩-沉积层边界界定的盆地底部形状对地震期间地面运动的时空分布的影响。到目前为止，几乎所有的研究都认为盆地的底部是凹陷的。最近的一篇科学文章表明，既包括凹面又包括凸面的底部表面可能会引起地面运动，这种运动是混乱的。这种混沌运动对工程结构所经历的地面运动水平的影响尚不清楚，但它可能是有益的。这将在二维沉积山谷中以入射平面SH波的形式受到地震激励的情况下进行探索。参数研究将确定凸底表面上方的地面运动与通常凹面形状上方的地面运动的差异。这项研究还将考虑山谷几何形状和地震激励的微小变化，如入射波的入射角度，是否会导致山谷响应的时空分布发生重大变化。如此大的变化将对地震危险性评估和结构的抗震设计具有重要意义。***

9319339 Bielak The 1985 Mexico earthquake focused attention on the amplification of strong ground motions when propagating from bedrock through the overlying sedimentary deposits. Similar situations may exist with regard to major cities in the United States, such as with the Los Angeles basin. The main objective of this research program is to investigate, by computer simulation, the effect of the shape of the bottom of the basin, as defined by the bedrock-sedimentary layer boundary, on the spatial and temporal distribution of surface ground motion during earthquakes. Practically all studies to date have considered the bottom of a basin to be concave. A recent scientific article suggests that a bottom surface which includes both concave and convex sections can cause ground surface motions which are chaotic. The effect of such a chaotic motion on the level of ground motion experienced by engineered structures is unknown, but it is likely to be beneficial. This will be explored in the context of two-dimensional sedimentary valleys subjected to seismic excitation in the form of incident plane SH waves. Parametric studies will determine the difference in the surface ground motion above a convex bottom surface as compared to that above the usual concave shape. This study will also consider whether small changes in valley geometry and seismic excitation, such as the angle of incidence of the incoming wave, can produce significant changes in the spatial and temporal distribution of the valley response. Such large variations would have important implications for seismic hazard assessment and the seismic design of structures. ***