基于有限断层源的核电厂设计基准地面运动估计

The traditional method to estimate design basis ground motion for nuclear power plant is using point-source based ground motion prediction equation. In the near field of large earthquake, however, point-source assumption may lead to unrealistic estimation due to the large dimension and complexity of the source. On the other hand, the time history of design basis ground motion generated by fitting response spectrum is not capable to describe the directivity and spatial correlation of ground motion. In this project, finite-fault assumption is adopted to replace point-source assumption. The model of finite-fault is built based on the information from site-specific survey of nuclear power plant; Broadband ground motion simulation with finite-fault model are adopted to replace ground motion prediction equation, based on which the effect of considering finite-fault source and realistic propagation path on design basis ground motion is investigated. The problem of estimating three components of ground motion by stochastic synthesis method is expected to be solved; a scenario earthquake based approach for generating the time history of design basis ground motion is proposed to replace the traditional spectrum-fitting approach. The effects of source on the directivity and spatial correlation of ground motion is then investigated. Based on previous researches and the improvements during the project, a systematic method to estimate design basis ground motion for nuclear power plant based on finite-fault model will be proposed, which is the pre-research of the improvement of design ground motion for major projects.

传统的核电厂设计基准地面运动，基于点源假设，采用地震动预测公式估计，与大地震能量释放机理的共识相悖，难以表征近场强地震动的复杂性，可能导致不合实际的结果；通过拟合目标谱人工生成的时程曲线，也难以体现地震动的方向性和空间相关性。鉴于此，本项目拟借助有限断层源，结合核厂址勘查成果，构建震源模型，替代点源假设，描述大地震的能量释放机理；借助基于有限断层源的宽频带地震动模拟，替代地震动预测公式，探讨考虑有限断层源和更真实、复杂的传播路径效应，对核电厂地震危险性评估的影响，并集中突破高频地震动随机合成法估计三平动分量的难题；提出借助设定地震估计基准地面运动时程的新思路，省却传统的目标谱拟合、人工调整工作，同时探索震源对基准地震动输入方向性和空间相关性的影响规律。结合前期研究基础，发现问题、不断改进，形成一套系统的基于有限断层源的核电厂设计基准地面运动估计方法，为改进重大工程设定地震动做出先期研究。

核电厂设计基本地面运动输入，是核岛结构地震响应和安全性评价的首要前提。传统的核电厂设计基准地面运动，基于点源GMPE估计，难以表征近场强地震动的复杂性，其结果可能是偏于保守亦或不安全；依靠拟合目标谱人工调整得到的时程曲线，也难以表达地震动的方向性和近断裂效应。项目借助有限断层源密切结合核场址勘查成果，构建设定地震有限断层震源模型，替代点源假设。震源模型包括全局和局部参数两部分：全局参数包括断层长度和宽度、断层的破裂面积以及平均滑动量，局部参数描述断层破裂面上的粗糙性及滑动的不均匀性，以凹凸体特征参数为主。考虑到核岛结构对高频地震动更为敏感，利用高频谱残差比选震源模型，满足空间相关性分析对震源模型唯一性的需求；借助基于有限断层源的宽频带地震动模拟方法，构建不同震源破裂机制下设定地震引起的地震动场，分析震源机制对地震动典型长周期成分和地震动相干性的影响规律。建立了考虑震源机制效应参数的地震动空间相干性模型以及脉冲型地震动脉冲特征预估模型，为核岛结构大底板地震动输入提供参考。利用时变频谱特征参数描述地震动时程频谱成分的过渡。将子源高频地震动的辐射模式与地震破裂发展过程联系起来，体现凹凸体是高频地震波的主要散射源，调整震源谱辐射水平标度因子，减小随机相位谱对合成地震动场空间特征的干扰；提出面向多阻尼反应谱拟合的增量时程误差排序的改进方法，同时提出匹配核电工程结构自振特性的种子时程选取方案。项目从上述几方面同时推进、不断改进，形成基于有限断层源的核电厂设计基准地面运动估计方法，是对目前宽频地震动混合模拟方法的一种工程推广，也可为核电厂地震安全性评估及防震减灾规划提供技术参考，研究过程中亦提炼出一些新的问题，值得今后继续深入。发表学术论文11篇，其中英文SCI 4篇、中文核心7篇。