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Title:: Analysis of the Seismicity of Two Types of Earthquake Sequences in Yanjin,Yunnan

作者:: 张演¹; 2; 姜金钟¹; 2; 王光明¹; 2; 张帅¹; 2; 何德强³; 周青云¹; 2; (1.云南省地震局,云南昆明 650224; 2.中国地震局昆明地震预报研究所,云南昆明 650224; 3.昭通市防震减灾局,云南昭通 657000)

Author(s):: ZHANG Yan¹; 2; JIANG Jinzhong¹; 2; WANG Guangming¹; 2; ZHANG Shuai¹; 2; HE Deqiang³; ZHOU Qingyun¹; 2; (1.Yunnan Earthquake Agency,Kunming 650224,Yunnan,China)(2.Kunming Institute of Earthquake Prediction,China Earthquake Administration,Kunming 650224,Yunnan,China)(3.Zhaotong Earthquake Preparedness and Disaster Reduction Agency,Zhaotong 657000,Yunnan,China)

Keywords:: the Delingha earthquake; earthquake relocation; focal mechanism; seismic tectonic background; Qinghai

摘要:: 2020年9月—2021年1月,云南盐津地区出现了密集中小地震活动。为获取更完备的地震目录和更准确的震源参数,利用2020年1月—2021年2月云南及其邻区地震台网记录到地震事件的观测报告和连续波形,采用匹配定位方法检测到了1 340次地震事件。利用联合波形互相关的双差地震定位方法进行重定位,获得了检测目录中351次地震的精确位置,对精定位后的地震活动时空分布特征进行分析研究,结果表明:盐津地区发生的密集中小地震活动为先后发生的2种不同类型的地震序列,沿两条不同走向和倾角的断裂分布,其中2020年9—10月的M_L3.9震群型地震序列发生在NNW走向、倾角约为75°的盐津—筠连断裂; 2021年1月的M_L5.2孤立型地震序列发生在近SN走向、断层线与盐津—筠连断裂呈约30°夹角且倾角约为50^°的隐伏断裂。

Abstract:: Based on the catalogue and waveforms of moderate- and small-earthquakes occurring in Yanjin area during September 2020 to January 2021,we use the Match and Locate(M&L)method to detect and locate weak events.A total of 1 340 events are detected by the M&L method,which are about 6.7 times the number of events listed in the Yunnan Seismic Networks Catalogue.We then obtain refined hypocenters of 351 detected earthquakes by simultaneously using P and S travel times and waveform cross-correlation data in the double-difference relocation algorithm.We also investigate the spatial-temporal characteristics of the detected earthquakes after double-difference relocation.Our results indicate that the moderate- and small-earthquakes occurring in Yanjin area during September 2020 to January 2021 could be categorized as two different types earthquake sequences:the M_L3.9 swarm mainshock type,and the M_L5.2 isolated earthquake.These two types of earthquake sequences occurred along two different faults with different strike and dip angles.The M_L3.9 swam sequence occurred on the Yanjin-Junlian fault with a strike of NNW direction and dip angle of about 75°,and the M_L5.2 isolated sequence occurred on a blind fault with a strike of near NS direction and a dip angle of about 50^°.