摘要
综合最新布设的龙门山断裂带地震空段台阵(LmsSGA)与四川省地震局固定地震台网数据,对龙门山断裂带新近一年(2016年11月21日到2017年10月28日)的23479个地震事件开展双差定位工作,共获取包括汶川地震余震和芦山地震余震在内的6111个重定位地震事件.在此基础上,分别与汶川地震和芦山地震的早期余震空间分布特征进行比较.研究发现在汶川地震发生近十年后,其余震活动依旧活跃.汶川地震现今余震活动主要分布在10~25km的深度区间,震源深度呈现西南段较东北段偏深的特征.此外,汶川近年余震分布相比早期余震偏深,破裂带西南段的余震活动有向深部迁移的趋势.对于芦山地震,其近期余震活动较弱,余震主要分布在10~15km的深度区间,比早期余震的分布区间偏浅.龙门山断裂带最新余震活动分布特征表明,余震活动随着时间的推移有迁移的现象.考虑到距离主震事件已分别有5~10年的流逝时间,余震迁移现象可能由以流体扩散方式为主的准静态应力机制触发.
Combining the newly established Longmenshan Seismic Gap Array(LmsSGA)with the permanent stations from Sichuan Earthquake Administration,we carry out double-difference location for 23479 events from November 21~(st),2016 to October 28~(th),2017 in Longmenshan Fault Zone and obtain 6111 relocated events including Wenchuan aftershocks and Lushan aftershocks.Comparing with the early aftershocks of Wenchuan event,we find that the aftershocks are still active after ~10 years of Wenchuan earthquake.The Wenchuan aftershocks mainly distribute between 10 to 25 km in depth,and the focal depths in the southwestern section are much deeper compared with the depths in the northeastern section.In addition,compared with the early aftershocks of Wenchuan earthquake,the distribution of the latest aftershocks is much deeper.The aftershocks migrate toward the deeper depth in the most recent years.However,the aftershocks of Lushan earthquake are relatively weak.Moreover,the depths are mainly located between 10 to 15 km,which are much shallower than the earlier aftershocks.The distribution of the latest aftershocks in Longmenshan Fault Zone shows that the aftershocks migrate in space with time.Considering that the elapse time has been 5~10 years after the two mainshocks respectively,we suggest that the aftershock migration may be triggered by quasi-static mechanism,such as fluid diffusion.