2022—2023年四川泸定M_(S)6.8、M_(S)5.0和M_(S)5.6地震序列的发震构造及成因  

Seismotectonics and seismogenesis of the 2022—2023 Sichuan Luding M_(S)6.8,M_(S)5.0 and M_(S)5.6 earthquake sequences

作　　者：张建勇 王新[3,4] 陈凌[2,4] 刘杰 ZHANG JianYong;WANG Xin;CHEN Ling;LIU Jie(China Earthquake Networks Center,Beijing 100045,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国地震台网中心,北京100045 [2]岩石圈演化国家重点实验室,中国科学院地质与地球物理研究所,北京100029 [3]中国科学院地球与行星物理重点实验室,中国科学院地质与地球物理研究所,北京100029 [4]中国科学院大学地球与行星科学学院,北京100049

出　　处：《地球物理学报》2024年第4期1471-1486,共16页Chinese Journal of Geophysics

基　　金：国家重点研发计划(2022YFF0802600);中国科协“青年人才托举工程”(2020QNRC001);中国地震台网中心青年科技基金(QNJJ-202204,QNJJ-202309)共同资助

摘　　要：四川泸定2022年9月5日发生M_(S)6.8强震,随后10月22日和2023年1月26日又分别发生M_(S)5.0和M_(S)5.6强余震,主震和两次强余震的震中相距仅几公里却有着截然不同的震源机制解,因此,探究三者的发震构造、联系及成因至关重要.本研究利用国家地震台网记录到的这三次地震序列的连续波形数据及震相资料进行双差重定位,并进一步采取CAP波形反演方法和P波初动极性反演方法获得研究区M_(L)2.5+的79个余震震源机制解.结果显示,主破裂沿鲜水河断裂磨西段,破裂彻底,余震活动性不高.沿主断裂分布的余震具有明显的分段特征,断层近直立且西北浅东南深.主震及磨西段大部分余震均为走滑机制,是典型的印度—欧亚板块挤压旋转造成鲜水河走滑断裂带应力失稳触发的强震活动.发生在贡嘎山地区的余震是M_(S)6.8主震触发的震群活动,震级水平不高,分布弥散,并没有触发与主断裂共轭的燕子沟、海螺沟和磨子沟次级断裂,而是触发了与主断裂近平行的次级隐伏断裂——贡嘎山断裂.M_(S)5.0和M_(S)5.6两次强余震均发生在该次级隐伏断裂上,断层倾角40°~50°且震源深度较浅.贡嘎山地区拉张型地震活动明显不同于走滑型为主的鲜水河断裂带,可能是印度—欧亚板块挤压旋转作用下贡嘎山快速隆升而地表快速剥离导致局部因重力卸载而垮塌造成的,M_(S)6.8主震有明显的触发作用.三次泸定强震的发生,释放了磨西段及西侧贡嘎山地区部分应力,但并未改变"Y"字形交汇区强震发生的可能性.The 2022 Sichuan Luding M_(S)6.8 earthquake occurred on 5 September 2022, followed by two strong aftershocks of M_(S)5.0 and M_(S)5.6 on 22 October 2022 and 26 January 2023, respectively. These three earthquakes occurred in close proximity both spatially and temporally, with their epicenters several kilometers apart but distinct focal mechanisms. Therefore, it is crucial to investigate the seismogenic structures and mechanisms associated with these earthquakes. In this study, the Luding earthquake sequences were relocated using the double-difference relocation algorithm, and 79 moment tensor solutions for earthquakes with local magnitude greater than 2.5 were determined by the waveform inversion method and the P-wave polarity inversion method. Our findings show that the main rupture occurred along the Moxi fault of the Xianshuihe fault zone, where the aftershock activity is less. The 2022 Luding earthquake sequence occurred on the nearly vertical Moxi fault, exhibiting obvious segmental characteristics, and the average depths of the sequence gradually increase from NW to SE. The mainshock occurred on a strike-slip fault and the focal mechanisms of aftershocks along the Moxi fault are similar to the mainshock. The occurrence of the M_(S)6.8 mainshock can be attributed to the stress destabilization of the Xianshuihe strike-slip fault zone caused by the extrusion and rotation of the India-Eurasia plate. The aftershocks beneath the Gongga Mountain area were cluster activities triggered by the M_(S)6.8 mainshock, with diffusely distributed locations and of small magnitude. They were likely the result of the M_(S)6.8 mainshock triggering a series of secondary blind faults, Gongga Mountain fault zone, which are subparallel to the main fault, but not triggering the Yanzigou, Hailuogou, and Mozigou secondary faults, which are conjugate to the main fault. The Luding M_(S)5.0 and M_(S)5.6 earthquake sequences occurred on this blind fault with a dip of 40°~50°, which is shallower than the Moxi fault. The focal mechanisms i

关 键 词：四川泸定地震 鲜水河断裂带 贡嘎山地区 发震构造 地震活动性 

分 类 号：P315[天文地球—地震学]