Abstract. In the complex medium system of sea area, the overlying sea water and the surface soft soil have a significant impact on the seafloor ground motion, which brings great seismic risk to the safety of offshore engineering structures. In this paper, four sets of typical free field models are constructed and established, which are land model, land model with surface soft soil, sea model and sea model with surface soft soil. The dynamic finite difference method is used to carry out two-dimensional seismic response analysis of typical free field based on the input forms about P and SV wave. By comparing the seismic response analysis results of four groups of calculation models, the effects of overlying seawater and soft soil on peak acceleration and acceleration response spectrum are studied. The results show that when SV wave is input, the peak acceleration and response spectrum of the surface of soft soil on the surface and the seabed surface can be amplified, while the overlying sea water can significantly reduce the ground motion. When P wave is used, the effect of overlying seawater and soft soil on peak acceleration and response spectrum of surface and seabed can be ignored. The peak acceleration decreases first and then increases from the bottom to the surface, and the difference of peak acceleration calculated by four free field models is not obvious. The results show that the overlying sea water and the surface soft soil layer have little effect on the peak acceleration of ground motion below the surface.

中文翻译：

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海底软土层对地震地震动的影响研究

摘要。在海域复杂介质系统中，上覆海水和表层软土对海底地震动有重大影响，给海上工程结构的安全性带来极大的地震危险。本文建立并建立了四套典型的自由场模型，分别是土地模型，地表软土模型，海模型和地表软土模型。基于P波和SV波的输入形式，采用动态有限差分法对典型自由场进行二维地震响应分析。通过比较四组计算模型的地震响应分析结果，研究了上覆海水和软土对峰值加速度和加速度响应谱的影响。结果表明，当输入SV波时，可以放大表层和海床表层的软土表层的峰值加速度和响应谱，而上覆的海水可以显着降低地震动。当使用P波时，上覆海水和软土对表面和海床的峰值加速度和响应谱的影响可以忽略。峰值加速度先降低后从底部增加到地面，由四个自由场模型计算得出的峰值加速度差异不明显。结果表明，上覆海水和地表软土层对地表以下地面运动的峰值加速度影响很小。而上方的海水会大大降低地面运动。当使用P波时，上覆海水和软土对表面和海床的峰值加速度和响应谱的影响可以忽略。峰值加速度先降低后从底部增加到地面，由四个自由场模型计算得出的峰值加速度差异不明显。结果表明，上覆海水和地表软土层对地表以下地面运动的峰值加速度影响很小。而上方的海水会大大降低地面运动。当使用P波时，上覆海水和软土对表面和海床的峰值加速度和响应谱的影响可以忽略。峰值加速度先降低后从底部增加到地面，由四个自由场模型计算得出的峰值加速度差异不明显。结果表明，上覆海水和地表软土层对地表以下地面运动的峰值加速度影响很小。四种自由场模型计算出的峰值加速度差异不明显。结果表明，上覆海水和地表软土层对地表以下地面运动的峰值加速度影响很小。四种自由场模型计算出的峰值加速度差异不明显。结果表明，上覆海水和地表软土层对地表以下地面运动的峰值加速度影响很小。