2019年四川长宁MS6.0地震序列重定位和震源特征分析

Relocation and source characteristics of the 2019 Changning MS6.0 earthquake sequence

采用双差定位方法对2019年1月1日至2019年10月20日期间四川区域台网记录到的地震进行重定位,得到7030个重定位事件,并获得了四川长宁MS6.0地震序列较准确的空间分布,并据此计算了震后长宁震源区的平均b值,分析了地震序列的活动性;利用近震全波形拟合方构深法东造,获浅获得的得了趋如主势下,震且主及西要4部结次地果MS:区≥①地5.0震四地的川震频长的度宁震远余源远震机高序制于列解东呈和部N矩W地-心区SE深;向②度分,b初布值倸步,空余分间震析分嬃深了布度本显分次示布地,整震震体后序呈长列现宁的出地发西区震呈现出明显的挤压构造环境;③主震和4次震级较大余震的矩心深度均较浅,尽管均为逆冲型为主的地震事件,但破裂面走向有所差异;④推测主震及中强余震是长宁背斜地区既有断裂或者同震过程中所产生的新生断层长期受到外力挤压而错断所致。

The double difference earthquake location algorithm is used to relocate the earthquakes occurred in Changning area of Sichuan Province,which recorded by Sichuan regional network from January 1,2019 to October 20,2019,7030 relocation events were obtained,and showing the clearer spatial distribution of Changning MS6.0 earthquake sequence.The average b-value of Changning focal area is calculated with relocated aftershocks catalog,and the seismicity of the earthquake sequence is analyzed.The focal mechanism solutions and centriod depth of the Changning main shock and 4 aftershocks with MS≥5.0 have been inverted with the local full-waveform inversion method,and the seismotectonics of this earthquake sequence was analyzed preliminarily.The main conclusions are as follow:①The Sichuan Changning aftershocks distribute in a NW-SE trending,and the aftershocks show a trending of deep in the West and shallow in the East,and the frequency of earthquakes in the western part is much higher than that in the eastern part;②The spatial distribution of b-value shows obvious compression tectonic environment in the Changning area after the occurrence of the earthquake;③The main shock and 4 moderate aftershocks occurred at unusual shallow centroid depths,and their focal plane solutions suggest that earthquakes occurred on thrust faults with slightly different strike;④It is speculated that the MS6.0 main shock and moderate aftershocks occurred on the preexisting faults,which subjected from a long-term compression force and the earthquake happened when the stress beyond the elastic limit,or the aftershocks generated on the newly generated faults created by mainshock coseismic rupture in Changning anticline area.