Earthquake Motion Characteristics of Reclaimed Ground in Osaka Bay Erea

大阪平原被山区包围，位于椭圆形盆地的东北部，包括大阪湾的一部分，长轴40公里，长轴80公里。大阪平原的地震运动受地形条件和地面条件的影响较大。本文在地震观测资料的基础上，研究了填海造地地震运动的持续时间、主导周期和放大特征。结果表明：(1)持续时间大阪平原地震运动的持续时间随周围山脉与平原位置的水平距离而变化；山地与平原交界地区的持续时间较短，而平原中部地区的持续时间明显较长。地震运动持续时间的这种变化不是由表面层条件的差异引起的，例如洪积层和冲积层之间的情况。这是由于下部S波的合成，对应于主运动，表面波在沉积层中水平传播，对应于延迟运动。(2)主要周期短周期(少于大约。1秒)在与主运动相对应的波的部分中占上风。主要的周期比大约短。1秒反射地面最上部的构造。周期大于约。1秒主要发生在与延迟运动相对应的波源部分。(3)放大特性在短于近似的周期频带内。1 .填海造地地震运动的放大特征因地下层结构的不同而有显著差异，最大可达约。在地表下60米。

The Osaka Plain is surrounded by mountainous regions and is located in the northeast of an oval-shaped basin, comprising part of the Osaka Bay, with a 40 km minor axis and 80 km major axis. The earthquake motions in the Osaka Plain are greatly influenced by the topographical conditions and the ground conditionsThis report studies the duration time, predominant period and amplification characteristics of earthquake motions in the reclaimed ground, based on the data gathered through earthquake observation.The discussion revealed the following :(1) Duration timeThe duration of earthquake motions in the Osaka Plain varies with the horizontal distance between the surrounding mountains and the location in the plain ; the duration time is short in areas on the border between the mountains and plain, while it is markedly longer in the central part of the plain. This variation in the duration of earthquake motions is not caused by the difference in the conditions of the surface layer, such as that between a diluvial layer and an alluvial layer. It results from the fact that the synthesis of S waves from below, corresponding to main motions, and surface waves propagated horizontally through the sedimentary layer, corresponding to delayed motions.(2) Predominant periodThe short periods (less than approx. 1 second) prevail in the portion of the wavefrom corresponding to main motions. The predominant periods shorter than approx. 1 second reflect the structure of the uppermost part of the ground. The periods longer than approx. 1 second mainly prevail at the portion of the wavefrom corresponding to the delayed motions.(3) Amplification characteristicIn the periodic band shorter than approx. 1 second, the amplification characteristics of earthquake motions in the reclaimed ground vary conspicuously according to the structure of subsurface layers, up to approx. 60 m under the surface.