2017年九寨沟MS7.0地震余震危险性概率分析

本文介绍了余震危险性概率分析的概念，完整列出其相关公式的解析表达式并阐述了余震危险性概率分析的具体方法。以2017年九寨沟M_S7.0地震为例，首先，求得该地震余震序列的相关参数，结果显示:九寨沟M_S7.0地震余震序列理论最大余震震级约为M_L5.3；b值约为0.784 1，明显低于中国西南地区同类型的其它地震，表明九寨沟地震余震区应力水平相对较高；p值约为1.109 7，明显高于中国西南地区同类型的其它地震，表明九寨沟地震余震序列随时间衰减较快。其次，计算此次地震余震与主震释放能量的比例关系，结果显示:在九寨沟M_S7.0地震事件中，截止到10月22日约99.69%的能量为主震所释放，0.31%的能量为余震所释放。最后，利用九寨沟M_S7.0余震序列参数结果并结合衰减关系，分别计算了主震后0—1天、1—10天、10—30天和90—100天内不同断层距内不同水平的峰值加速度和峰值速度的超越概率，结果显示:随着断层距增加，在相同时间间隔内超越概率的值呈下降趋势；在震后第一天内余震危险性最高，随着震后时间增加，相应的超越概率值呈现出明显下降趋势，表明九寨沟M_S7.0地震余震危险性主要来自早期余震。本文的相关成果可以为震后地震危险性分析提供参考，并为短时间内应急救援及灾后重建提供辅助决策意见。 

Probabilistic aftershock hazard assessment for Jiuzhaigou MS7.0 earthquake in 2017

Probabilistic aftershock hazard assessment is important to assess the hazard of aftershocks. In this paper, we introduce the concept of probabilistic aftershock hazard assessment, and give the formulas related to the method of it.In response to the Jiuzhaigou M_S7.0 event in Sichuan Province in 2017, firstly, we obtained the related parameters of the aftershock. The results show that the maximum aftershock magnitude of the given aftershock sequence is about M_L5.3. The b value of Jiuzhaigou event is about 0.784 1, which is lower than the same type of earthquake in southwest China, indicating that the stress level of the aftershock area is relatively high. The p value is about 1.109 7, obviously higher than events of the same type, which shows that this aftershock sequence decays faster with time. Secondly, according to the parameters estimation, 99.69% of the energy was released by the mainshock and the rest by the aftershocks. Finally, combining the aftershock sequence parameter and the attenuation relationship, we calculated the probability of exceedance certain level of peak ground acceleration and peak ground velocity in 0?1 day, 1?10 days, 10?30 days and 90?100 days intervals within different fault distances after the mainshock. The results show: ① The value of exceedance probability decreases with fault distance in the same time interval; ② The risk of aftershocks is highest in the first day after the mainshock; the exceedance probability value exhibits a downward trend with the increase of time, indicating that the aftershock hazard of the JiuzhaigouM_S7.0 event mainly comes from early aftershocks. These results provide reference for aftershock risk analysis, and auxiliary decision-making opinions for short time emergency rescue and post disaster reconstruction.