四川长宁地区地震活动空间分布特征研究

Study on the Spatial Distribution of Seismic Activity in Changning Area,Sichuan Province

摘要:

近年来,四川长宁地区地震活动频繁,特别是2019年6月17日发生的长宁 M_S6.0 地震造成长宁及周边地区较为严重的人员伤亡和财产损失,引起社会和科研工作者的广泛关注。为探究长宁地区地震的发震构造和机理,利用双差定位方法对长宁 M_S6.0 地震前后一年时间段内的地震进行重定位,并采用波形拟合方法获得了14次M_S＞4.0地震的震源机制解,综合分析了长宁地区地震活动的空间分布特征,获得以下主要认识:①2019年长宁 M_S6.0 地震的发震构造为长宁背斜NW向的高倾角断层,地震序列的震源深度西深东浅,该地震是位于滑脱面之上先存断裂活化的构造地震事件; ②南部建武向斜地区地震活动频度高,且表现出丛集性的分布特征,推测与零散分布的页岩气开采活动密切相关; ③长宁地区南北2个区域地震活动的差异性受控于局部应力场方向的变化,北侧历史盐矿开采、南侧页岩气开采以及岩石介质物性的横向差异直接影响了地震的空间特征。

Abstract:

In recent years,seismic activity in Changning area of Sichuan Province has been relatively high,especially for the M_S6.0 earthquake in June 2019,which has been brought wide attention of society and scientific researchers. In this study,we used the double-difference method to relocate the earthquakes within one year before and after the M_S6.0 earthquake. Further,we applied the gCAP waveform fitting method to obtain the focal mechanism solution of 14 earthquakes with M_S>4.0. The spatial distribution characteristics of seismic activities in Changning area was comprehensively analyzed,and the following main understandings were obtained:① The seismogenic structure of the M_S6.0 earthquake in 2019 was the high-dip thrust fault with NW direction in the Changning anticline,and the focal depth of the seismic sequence was deep in the west and shallow in the east,indicating the reactivation of the pre-existing fault in NW direction. ② The frequency of seismic activity in the Jianwu anticline area in the south is relatively higher and shows the characteristics of cluster distribution,which is speculated to be closely related to shale gas exploitation activities. ③ The difference of seismic activity between the north and the south of Changning area is controlled by the change of the direction of the local stress field. The historical salt mining in the north and shale gas mining in the south,as well as the horizontal difference of the physical properties of rock medium directly affect the spatial pattern of seismic distribution.