Probabilistic aftershock hazard assessment for Jiuzhaigou M_S7.0 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.