Abstract:

At 01:45 on January 8, 2022, Beijing Time, an M_S6.9 earthquake occurred in Menyuan County, Haibei Prefecture, Qinghai Province, with a focal depth of 10km. The microscopic(instrument)epicenter is located at 37.77°N latitude and 101.26°E longitude in the intersection between the Toleshan fault zone and the Lenglongling fault zone in the northern Qilian-Qaidam block. The epicenter is 54km away from Menyuan County in Qinghai, 99km away from Qilian County, 100km away from Haiyan County, 83km away from Minle County in Gansu Province, 83km away from Yongchang County, and 141km away from Xining City. When the earthquake occurred, Menyuan County and Xining City, the capital of Qinghai Province, were strongly felt, and Yinchuan, Lanzhou, Xi'an and many other places were felt. At the same time, affected by the earthquake, the Lanxin high-speed rail line, an important railway transportation hub of the Belt and Road, was suspended. This earthquake is the largest earthquake in the world since 2022. It is also another earthquake of magnitude 6.0 or above in Qinghai Province following the Maduo M_S7.4 earthquake on May 22, 2021. Besides, this earthquake is the event with the highest magnitude and the longest surface rupture in the region after the two M6.4 Menyuan earthquakes of August 26, 1986 and January 21, 2016. Therefore, this earthquake has attracted much attention from the society. The coseismic surface rupture distribution, combination characteristics, development properties and coseismic displacement of this earthquake were identified in time to help to have a correct understanding of the earthquake seismogenic structure, rupture process, and assessment of short-term earthquake hazards. It is also of great significance for major project route selection, earthquake fortification and rescue and disaster relief. On the basis of the on-site seismic geological investigation, based on the interpretation and analysis of high-resolution satellite remote sensing images, and combined with the low-altitude photogrammetry of unmanned aerial vehicles(DJI PHANTOM 4RTK), the author obtained the coseismic rupture data of five typical sites along the surface rupture zone generated by the earthquake. Using Agisoft Metashape Professional software to process the aerial photos of each section indoors, a high-resolution orthophoto map(DOM)was generated. At the same time, the five typical earthquake surface rupture sections were described in detail in ArcGIS Pro software based on the orthophoto map. Preliminary research shows that the surface rupture zone of the Menyuan M_S6.9 earthquake is more than 22km long and consists of the main rupture of the northern branch and the secondary rupture of the southern branch. The north branch main rupture zone is distributed in the middle-western segment of the Lenglongling Fault of central Haiyuan fault zone, with a length of more than 18km and an overall strike of 295°. The maximum co-seismic horizontal displacement is located in the middle of the rupture zone at Liuhuangou(37.799°N, 101.2607°E), which is about 3.1m and gradually decays towards both ends. The secondary rupture of the southern branch is distributed on the local segments of the eastern Toleshan Fault in the central-western Haiyuan fault zone, with a length of about 4km and a strike of 275°, constituting a secondary branch rupture zone arranged in a left-stepped en-echelon pattern to the western segment of the main rupture zone. There are en-echelon extensional stepovers between the two rupture zones of the north and south branches. The whole surface rupture zone is mainly composed of linear shear cracks, oblique tension cracks, tension-shear cracks, compressional bulges and other structural types. The coseismic surface rupture has the characteristic of typical left-lateral strike-slip motion with a thrust component, and the maximum vertical dislocation is 0.8m.

Key words: Menyuan M_S6.9 earthquake, coseismic surface rupture, left-lateral strike-slip, Lenglongling Fault, Qinghai-Tibet Plateau

摘要：

北京时间2022年1月8日01时45分, 青海省海北藏族自治州门源回族自治县境内发生 M_S6.9 地震, 震源深度10km, 震中位于青藏高原中北部的祁连-柴达木次级地块的北部、 托莱山断裂带和冷龙岭断裂带的交会部位。此次地震是进入2022年以来全球震级最大的一次地震, 也是青海省境内继2021年5月22日玛多 M_S7.4 地震后又一次6.0级以上地震, 同时也是继1986年8月26日和2016年1月21日2次门源6.4级地震之后该地区发生的震级最高、 地表破裂最长的地震事件。在综合分析震源参数、 余震分布的基础上, 我们第一时间对同震地表破裂进行了野外考察。初步调查表明, 此次门源 M_S6.9 地震的地表破裂带长度>22km, 由北支主破裂和南支次级破裂组成。 其中, 北支主破裂带沿广义海原断裂带中段的冷龙岭断裂西段分布, 长度>18km, 主体呈295°走向, 最大同震水平位错位于中部硫磺沟一带(37.799°N, 101.260 7°E), 水平最大位错量约3.1m, 向两端逐渐衰减; 南支的次级破裂分布在广义海原断裂带中西段的托莱山断裂东段局部段上, 长约4km, 呈275°走向, 水平位错约1.0m, 构成与主破裂带西段左阶斜列的次级分支破裂。南、 北2支破裂段之间以拉张阶区斜列。整个地表破裂主要由线性剪裂隙、 斜列张裂隙和张剪裂隙、 挤压鼓包等多种构造类型组合而成。同震地表破裂具有典型的左旋走滑运动性质, 同时兼有逆冲分量, 最大垂直位错为0.8m。

关键词: 门源M_S6.9地震, 同震地表破裂, 左旋走滑, 冷龙岭断裂, 青藏高原