Seismic Ground Motion in Sedimentary Valleys: Focusing or Chaos?

9319339 Bielak 1985年墨西哥地震集中注意力在强地面运动从基岩通过覆盖的沉积物传播时的放大。 类似的情况可能存在于美国的主要城市，例如洛杉矶盆地。 本研究计划的主要目标是通过计算机模拟，调查盆地底部形状的影响，定义为岩石-沉积层边界，地震时地面运动的空间和时间分布。 实际上，迄今为止的所有研究都认为盆地的底部是凹的。 最近的一篇科学文章表明，包括凹部和凸部的底表面可以引起混乱的地面运动。 这种混沌运动对工程结构所经历的地面运动水平的影响是未知的，但它可能是有益的。 这将在二维沉积山谷的背景下进行探讨，以入射平面SH波的形式进行地震激发。 参数研究将确定与通常的凹形表面相比，凸形底部表面上的地面运动的差异。 本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，是否会导致山谷响应的空间和时间分布发生重大变化。 如此大的变化将对地震危险性评估和结构的抗震设计产生重要影响。 ***

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. ***