考虑震源不确定性的地震动多元概率分布模型研究

The quantitative evaluation of the ground-motion variability has always been a hot topic in the field of earthquake engineering. The seismic source, which exerts vital influences on ground motions, is one of the key reasons responsible for the ground-motion variability. This study aims to quantitatively evaluate the ground-motion variability, individually caused by the stress drop, rupture process, and rupture directivity. The sample sets of the target event are established to reflect the variability of stress drop, rupture process, and rupture directivity, respectively. An improvement of the two-stage stochastic empirical Green’s function method is proposed to extend its application for the events the predominantly unilateral rupture. In this study, this method is applied to simulate ground motions for the target events considered. According to the hypothesis test, the probabilistic distribution models of the simulated ground motions, which are produced respectively by the uncertain stress drop, random rupture process, and uncertain rupture directivity, are constructed. The characteristic parameters in the distribution model are calculated to quantitatively describe the variability of simulated ground motions. Then, we develop the quantitative relationships between the characteristic parameters and uncertain stress drop, complex and random rupture process, as well as rupture directivity following specific probability distribution, respectively. Finally, under these study results, we propose the multivariate probability distribution of the ground motion generated by complicated seismic source. The probability seismic hazard analysis is used to verify the reliability of the established model. The results from this study can be directly used in the probability seismic hazard analysis, city hazard evaluation from active fault, theory study and application on the source, and rapid generation of the ground motion filed.

地震动不确定性的定量评估一直是地震工程领域研究的热点问题，地震震源对地震动有至关重要的影响，是造成地震动不确定性的重要原因之一。本项目针对应力降、震源破裂过程及震源破裂方向性引起的地震动不确定性开展定量评估，分别建立体现应力降、震源破裂过程及震源破裂方向性的不确定性的目标地震样本集，提出适用于模拟不均匀破裂地震的改进的两步随机经验格林函数方法，模拟典型地震实例的地震动，利用假设检验提出不确定的应力降、震源破裂过程及震源破裂方向性分别产生的模拟地震动的概率分布模型，计算模拟地震动的概率模型的特征参数，建立应力降、震源破裂过程、震源破裂方向性的不确定性与这些特征参数的定量关系，最后构建不确定的震源产生的地震动的多元概率分布模型，并通过概率地震危险性分析检验模型可靠性。本研究可直接用于地震危险性分析、城市活动断层灾害评估、震源理论研究及地震动场快速产出等研究工作。

定量评估地震动不确定性对地震危险性、地震风险区划等防震减灾工作具有至关重要的作用，地震震源是影响地震动的三个关键要素之一，可造成地震动大的不确定性。基于两步随机经验格林函数和随机有限断层方法的大量地震动模拟记录研究地震震源相关因素，包括地震应力降、震源随机破裂过程、震源破裂方向性对地震动不确定性的定量影响。应力降相关的地震动反应谱不确定性与应力降不确定性和谱周期相关，随谱周期增大地震动反应谱对数标准差与应力降对数标准差的比值逐渐减小，且减小速率逐渐增大，同时应力降对数标准差越大则该比值越小，当应力降对数标准差为0.3时该比值从0.05s的0.7逐渐降低至5.0s的0.5，最终建立了地震应力降相关的地震动不确定的定量模型。大量不同随机破裂过程的模拟地震动近似服从对数正态分布，地震动反应谱对数标准差整体上在0.05-0.15之间，且随谱周期增大而增大，距离对地震动反应谱对数标准差也有影响，随距离增大呈下降趋势，最终考虑谱周期和距离的影响，建立了随机破裂过程相关的地震动不确定性的定量模型。破裂方向性引起地震动在空间上具有显著的不确定性，破裂方向性相关的地震动不确定性与距离、方位角、谱周期相关，整体上随距离增大呈先增大后减小的趋势，随着方位角与破裂面走向之间夹角的增大整体上呈减小趋势，随谱周期增大而减小，沿破裂面走向的近场区域地震动短周期反应谱的加权对数标准差可达0.25，最终考虑谱周期、距离和方位角的影响，建立了破裂方向性相关的地震动不确定性的定量模型。本项目的研究结果可直接应用于地震危险性、地震风险区划等防震减灾工作。