2022年四川马尔康M_(S)6.0强震群重定位及发震断层探讨  

RELOCATION OF THE 2022 M_(S)6.0 MAERKANG EARTHQUAKE SWARM IN SICHUAN PROVINCE AND ITS SEISMIC FAULT ANALYSIS

作　　者：许英才[1] 郭祥云[2] XU Ying-cai;GUO Xiang-yun(Earthquake Agency of Ningxia Hui Autonomous Region,Yinchuan 750001,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China)

机构地区：[1]宁夏回族自治区地震局,银川750001 [2]中国地震局地球物理研究所,北京100081

出　　处：《地震地质》2023年第4期1006-1024,共19页Seismology and Geology

基　　金：国家重点研发计划项目(2017YFC1500501);宁夏自然科学基金(2022AAC03687);中国地震局震情跟踪定向工作任务(2023010113,2022010104,2021010118)共同资助

摘　　要：2022年四川马尔康强震群是中国有地震台网记录以来,巴颜喀拉块体东部马尔康地区首次出现的地震频度高、时空分布集中、爆发性较强且震级强度大的罕见强震群活动。文中通过双差定位方法对该震群序列进行了重定位,利用gCAP方法测定了M_(S)≥3.6地震的震源机制及矩心深度,然后根据震源机制结果分析了马尔康地区应力体系与这些地震震源机制的关系,最后根据重定位结果进行了断层面拟合。结果显示,马尔康震群序列震中区域主要沿NW向优势分布,整个震群序列的平均初始破裂深度为9.8km,深度剖面反映地震相对密集的区域主要介于0~15km深度之间,震群中震级最大的M_(S)6.0地震的初始破裂深度为12.5km,几乎位于震群序列密集区的底端。其震源机制节面I的走向为150°,倾角为79°,滑动角为7°;节面Ⅱ的走向为59°,倾角为83°,滑动角为169°;矩心深度为9km。其余M_(S)≥3.6地震的震源机制均为走滑型,震源机制节面的倾角为71°~86°,且相同走向的各个节面的倾向也有所不同,其矩心深度为5~9km,P轴方位为NWW向,且倾伏角近水平。M_(S)≥3.6地震震源机制NW向节面的相对剪应力均显著大于NE向节面,且NW向节面的正应力均小于NE向节面,表明这些地震更容易在NW向的节面上产生走滑错动。拟合后的断层面参数揭示震群中大部分地震活动可能受到马尔康断裂附近至少2条近NW走向的平行伴生断层控制,倾角约为88°,且具有左旋运动性质。结合已有的区域地质构造推测,马尔康震群可能为NW向和NE向共轭断层发震,其中NW向断层控制了大多数地震活动。The 2022 M_(S)6.0 Maerkang earthquake swarm in Sichuan Province is the first rare strong swarm activity with high frequency,concentrated spatial and temporal distribution,strong explosive and strong magnitude in Maerkang area in the eastern segment of Bayan Har block in China seismic network records.It is also another significantly strong earthquake event in Bayan Har block after the M_(S)7.4 Maduo earthquake on May 22,2021.The M_(S)6.0 Maerkang earthquake on June 10,2022 not only broke the 33-year record without M_(S)≥6.0 earthquakes within 100km of the epicenter,but also broke the historical record without M_(S)≥6.0 earthquakes within 50km of the epicenter.The earthquake swarm is mainly located in the nearly“T”shaped conjugate fault structure area composed of the NW strike Maerkang fault and NE strike Longriba fault in the Bayan Har block.This area is a relatively rare region for moderate and strong earthquakes in the history.Therefore,it is of great significance to analyze and discuss the possible seismogenic faults of the Maerkang strong earthquake sequence for the study of seismogenic structures and the risk of strong earthquakes in the weak seismic region of Bayan Har block.The earthquake swarm was relocated by double-difference method,and focal mechanisms and centriod depths of M_(S)≥3.6 earthquakes were calculated by using gCAP inversion method.Then the relationship between the stress system in the Malkang area and these earthquake focal mechanisms was analyzed,and fault plane was fitted by using relocation results.Maerkang earthquake swarm is mainly distributed along NW direction,and the initial rupture depth is 9.8km on average.Depth profiles show that earthquakes are mainly concentrated at depth between 0km to 15km.The most earthquakes of early-stage occurred in 48 hours.The mid-stage and late-stage earthquakes are located less than 15km in depth and move to the northwest of the epicenters.Initial rupture depth of the largest M_(S)6.0 earthquake is 12.5km,which is almost at the bottom of the

关 键 词：马尔康震群 重定位 震源机制 滑动特性 发震断层 

分 类 号：P315.2[天文地球—地震学]