Earthquake Motion Characteristics of Reclaimed Ground in Osaka Bay Erea

大阪平原被山区包围，位于一个椭圆形盆地的东北部，该盆地由大阪湾的一部分组成，短轴40公里，长轴80公里。大阪平原的地震活动受地形条件和地面条件的影响很大。本文根据地震观测资料，研究了围垦地区地震活动的持续时间、优势周期和放大特征。讨论表明：(1)持续时间大阪平原的地震活动持续时间随周围山脉与平原所处的水平距离而变化；持续时间在山地与平原交界处较短，而在平原中部明显较长。地震活动持续时间的这种变化不是由表层条件的差异引起的，例如洪积层和冲积层之间的条件差异。这是由于S波从下向合成，对应于主运动，而面波在沉积层中水平传播，对应于延迟运动。(2)优势周期短周期(小于约1秒)在对应于主运动的波形部分占优势。主要周期短于大约。1秒反映地面最上面部分的结构。该周期长于大约。1秒主要集中在延迟运动对应的波形部分。(3)放大特性：在短于约x的周期频带内。1.填海地震动的放大特性随次表层结构的不同而有明显的差异，最大可达1。在地表下60米处。

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.