詹艳^1,2,,
梁明剑^3,,
孙翔宇^1,2,
黄飞鹏^1,2,
赵凌强⁴,
宫悦³,
韩静^1,2,
李陈侠⁵,
张培震^1,6,
张会平^1,2,,
1. 中国地震局地质研究所 地震动力学国家重点实验室, 北京 100029
2. 中国地震局地质研究所 西藏拉萨地球物理野外观测站, 拉萨 850004
3. 四川省地震局 中国地震局成都青藏高原地震研究所, 成都 610041
4. 中国地震局第二监测中心, 西安 710043
5. 陕西省地震局, 西安 710068
6. 中山大学 地球科学与工程学院, 广州 510275

基金项目: 国家自然科学基金项目（41474057），地震行业科研专项（20130811）资助


详细信息

作者简介: 詹艳, 女, 1969年生, 研究员, 主要从事电磁方法、深部电性构造探测研究.E-mail:zhanyan66@vip.sina.com
梁明剑, 男, 1979年生, 高级工程师, 主要从事活动构造、地震危险性评价等方面工作.E-mail:23800794@qq.com

通讯作者: 张会平, 男, 1978年生, 研究员, 主要从事构造地貌、河流地貌及其年代学等方面的研究工作.E-mail:huiping@ies.ac.cn

中图分类号: P541;P319

收稿日期:2021-05-28
修回日期:2021-06-05
上线日期:2021-07-10

Deep structure and seismogenic pattern of the 2021.5.22 Madoi (Qinghai) M_S7.4 earthquake

ZHAN Yan^1,2,,
LIANG MingJian^3,,
SUN XiangYu^1,2,
HUANG FeiPeng^1,2,
ZHAO LingQiang⁴,
GONG Yue³,
HAN Jing^1,2,
LI ChenXia⁵,
ZHANG PeiZhen^1,6,
ZHANG HuiPing^1,2,,
1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China
2. Lhasa National Geophysical Observation and Research Station, Institute of Geology, China Earthquake Administration, Lhasa 850004, China
3. Earthquake Administration of Sichuan Province, Chengdu 610041, China
4. The Second Monitoring and Application Center, China Earthquake Administration, Xi'an 710043, China
5. Earthquake Administration of Shaanxi Province, Xi'an 710068, China
6. School of Earth Sciences and Engineering, Sun Yat-Sen University, Guangzhou 510275, China


More Information

Corresponding author: ZHANG HuiPing,E-mail:huiping@ies.ac.cn

MSC: P541;P319

--> Received Date: 28 May 2021
Revised Date: 05 June 2021
Available Online: 10 July 2021


摘要
摘要:2021年5月22日2时4分，青海省果洛藏族自治州玛多县发生M_S7.4地震，截至5月27日，已记录余震2700多次.本次地震震源深度17 km，震中坐标为34.59°N，98.34°E，位于巴颜喀拉块体北边界东昆仑断裂带以南70 km左右，结合震中位置、余震分布、卫星影像解译及活动断裂分布，初步判断发震断裂为东昆仑断裂带南部的玛多—甘德断裂带.本文展示了沿玛多地震震中西北20 km，长约280 km的北东向大地电磁探测结果，揭示主震震源及余震主体位于中下地壳高导与上部高阻体交界部位；对比巴颜喀拉块体东、北边界的不同震例的大地电磁探测结果，发现区域尺度上巴颜喀拉块体及其边界断裂带发生的中强地震震源多位于块体边界显著电性边界带附近.东昆仑断裂玛曲段三条电磁剖面揭示出与本次玛多地震相似的深部构造背景，由于古地震、历史地震资料揭示出玛曲—玛沁段最后一次地震事件的离逝时间已经超出或接近其复发周期，因此后续需重点关注玛曲—玛沁段的地震活动性及危险性.综合分析巴颜喀拉块体地质、地貌及深部电性结构特征，我们认为，玛多—甘德断裂带与巴颜喀拉块体内部其他北西向左旋走滑断裂，控制了诸如1947年达日M_S7.7地震、2021年玛多M_S7.4地震的发生，活动速率相对较低，强震复发间隔相对偏长；走滑速率更高的东昆仑、甘孜—玉树—鲜水河等边界断裂带，控制着边界断裂带内如2001年昆仑山口8.1级地震、2011年玉树7.1级地震等大震、强震的发生，地震复发间隔短；两种不同规模、不同运动速率的断裂体系协同运动，共同调节着青藏高原不同块体的形变，变形过程更为弥散连续，明显有别于中国大陆内部如塔里木、柴达木、鄂尔多斯、扬子等更为刚性的块体.巴颜喀拉块体内部沿龙日坝断裂、五道梁—长沙贡玛断裂等地区仍存在一定的地震空区，建议后续加强地震地质、深部孕震环境等研究工作.本文大地电磁探测结果表明，巴颜喀拉块体北边界带中下地壳高导层厚度明显小于东部地区，我们推测龙日坝断裂西北侧阿坝次级块体内构造变形以左旋走滑的水平向运动为主，中下地壳增厚有限，但龙日坝断裂东南至龙门山构造带之间龙门山次级块体内，中下地壳的缩短增厚幅度明显偏大，表明西北侧的水平走滑运动不断被龙日坝断裂东南地区的构造缩短增厚所吸收，控制着龙门山断裂带及邻区的构造变形与强震（如松潘、汶川、九寨沟地震等），同时驱动着青藏高原东缘晚新生代以来的快速侵蚀剥露及地貌演化进程.
关键词: 2021年玛多M_S7.4地震/
巴颜喀拉块体/
大地电磁/
深部结构/
动力学

Abstract:The Madoi M_S7.4 earthquake occurred at 2:04 on May 22, 2021, in Madoi County, Tibetan Autonomous Prefecture of Golog, Qinghai Province. As of May 27, there were~2700 aftershocks. The depth of this earthquake is 17 km. The epicenter is located at 34.59° north and 98.34° east. The location of the Madoi earthquake is ~70 km south of the East Kunlun Fault Zone at the northern boundary of the Bayan Har block. Combining the epicenter location, aftershock distribution, high-precision satellite image interpretation, and active fault distribution, the preliminary judgment of the seismogenic fault is the Madoi-Gadê Fault Zone in the southern part of the East Kunlun Fault Zone. In this paper, we present the results of the magnetotelluric profile along the 20 km northwest of the epicenter of the Madoi earthquake, with a length of about 280 km, revealing that the source area is located at the junction of the high conductivity and high resistivity bodies in the middle and lower crust. Comparing the magnetotelluric results of different earthquakes at the eastern and northern boundaries of the Bayan Har block, we find that the sources of moderate-strong earthquakes occurring in the Bayan Har block and its boundary fault zones are mostly located at the electrical boundary zone. The three electromagnetic profiles of the Maqu section of the East Kunlun Fault reveal a similar deep tectonic background to that of the Madoi earthquake. Since the paleoseismic and historical seismic data reveal that the last seismic event in the Maqu-Maqên section of the East Kunlun fault has exceeded or is close to its recurrence cycle, it is necessary to focus on the seismicity and risk of this section.
Based on a comprehensive analysis of the geology, geomorphology, and deep electrical structure of the Bayan Har block, we believe that the Madoi-Gadê fault and other northwest oriented left-slip faults within the Bayan Har block controlled occurrences of earthquakes such as the 1947 Dari M_S7.7 earthquake and 2021 Madoi M_S7.4 earthquake. These faults have a long interval of earthquake recurrence. Boundary faults such as the East Kunlun fault and Garzê-Yushu-Xianshuihe fault, which have higher slip rates, controlled the occurrences of the 2001 Kunlunshan M8.1 earthquake, 2011 Yushu M7.1 earthquake, and other strong earthquakes. Earthquake recurrence of these faults is short. The two kinds of fault systems with different scales and slip rates move in concert, making the deformation process more diffuse and continuous. They regulate the deformation of different blocks on the Tibetan Plateau, which are different from the more rigid blocks such as the Tarim, Qaidam, Ordos, and Yangtze blocks in mainland China. There are still some seismic gaps inside the Bayan Har block along the Longriba fault and the Wudaoliang-Changshagongma fault. It is suggested to strengthen the research work on seismic geology and deep seismogenic environment in the future. The results of magnetotelluric sounding in this paper show that the thickness of the high conductive layer in the middle and lower crust of the northern boundary zone of the Bayan Har block is significantly smaller than that in the eastern region. It is assumed that the tectonic deformation in the Aba sub-block on the northwest side of the Longriba fault is dominated by the horizontal motion of the left slip. The thickening of the middle and lower crust is smaller. However, the shortening and thickening of the middle and lower crust within the Longmenshan sub-block between the southeast of the Longriba fault and the Longmenshan fault zone is significant, indicating that the shortening and thickening continuously absorb the horizontal slip movement on the northwest side in the southeast of the Longriba fault. This long-term tectonic deformation process gradually converts into vertical uplift in the Longmenshan fault zone and the area to the west (e.g., Songpan earthquake, Wenchuan earthquake, and Jiuzhaigou earthquake), further promoting the rapid erosion and denudation and geomorphological evolution process since the Miocene on the eastern margin of the Tibetan Plateau.
Key words:2021 Madoi M_S7.4 earthquake/
Bayan Har block/
Magnetotelluric/
Deep structure/
Geodynamics



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