Analysis on the characteristics of surface rupture and regional seismicity trend of Mengyuan M6.9 earthquake in Qinghai Province
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摘要:
据中国地震台网正式测定，2022年1月8日1时45分青海海北州门源县发生6.9级地震，震源深度10 km。此次地震是2016年门源M6.4级地震之后冷龙岭地区再次发生强震活动。此次地震的宏观震中位于距门源县城浩门镇西北50 km的冷龙岭硫磺沟地区，并在硫磺沟—大西沟一带形成规模大且连续性较好的地表破裂。地表调查显示，同震地表破裂的总长度约为23 km，整体走向N40°~85°W，地表破裂主要由雁列的地震鼓包、张裂缝、剪切裂缝等形式组合而成，而且地表伴生了较多规模不等的滑坡、崩塌等次生地质灾害。根据地表破裂的规模、走向及破裂特点等，可将其分为3段：东段（硫磺沟段），长约10 km，走向N40°~60°W，破裂规模较小，以伴有重力作用的拉张裂缝为主；中段（道沟段），长约9 km，走向N70°W，破裂规模较大，以发育规模较大的地震鼓包和剪切裂缝为主，而且左旋位移较大；西段（大西沟段），长约4 km，走向N85°W，此段规模最小，以雁列的拉张裂缝为主。其中—东段一起组成了该破裂带的东支，而西段构成了西支，两者都具有明显的左旋走滑特征，并自东向西破裂整体呈左阶展布，在G227国道以东形成了具有拉张特征的左阶阶区。综合分析表明，此次，地震发生在祁连山块体的祁连−海原活动构造带，发震断裂应为海原左旋走滑断裂带的冷龙岭−托莱山断裂段。结合对祁连−海原构造带1900年以来强地震序列及托莱山断裂的初步研究认为，该构造带的历史地震活动整体具有不断向西发展的趋势，但在哈拉湖和托莱山之间存在较明显的地震空区，因而推断托莱山断裂未来的强震危险性有增强的可能。
Abstract:The National Seismological Network officially determined that an earthquake of magnitude 6.9 occurred in Menyuan County, Haibei Prefecture, Qinghai, at 01:45 on January 8, 2022, with a focal depth of 10 km. This earthquake is another strong earthquake activity in the Lenglongling area after the 2016 Menyuan M6.4 earthquake. The macro-epicenter of the earthquake was located in the Liuhuanggou area of Lenglongling, more than 50 kilometers northwest of Chenghaomen Town, Menyuan County, and a large-scale and well-continued surface rupture was formed in the area of Liuhuanggou−Daxigou. Surface surveys show that the total length of coseismic surface ruptures is about 23 km, and the overall trend is N40°~85°W. Surface rupture is mainly composed of echelon earthquake bulge, tensile crack and shear crack, and there are many secondary geological disasters such as landslides and collapses on the surface. According to the scale, strike and fracture characteristics of the surface rupture, it can be divided into three sections: the eastern section (Liuhuanggou section), about 10 km long, strikes N40°~60°W, the scale of the rupture is small, and it is accompanied by gravity. The middle section (Daogou section), about 9 km long, strikes N70°W, with a large scale of rupture, mainly developed large-scale seismic bulges and shear fractures, and large left-handed displacement; The western section (Daxigou section) is about 4 km long and strikes N85°W. This section is the smallest in scale and is dominated by extensional fractures in the geese. The middle and eastern sections together form the eastern branch of the fracture zone, while the western section forms the western branch, both of which have obvious left lateral strike slip characteristics, and it ruptures from east to west, showing a left step distribution as a whole, forming a left step area with tensile characteristics east of G227 National Highway. To the east, a left-order region with extensional features is formed. Comprehensive analysis shows that the earthquake occurred in the Qilian−Haiyuan active tectonic belt of the Qilian Mountains block, and the seismogenic fault should be the Lenglongling−Tuolaishan fault section of the Haiyuan left-lateral strike-slip fault belt. Combined with the preliminary research on the strong earthquake sequence of the Qilian−Haiyuan tectonic belt since 1900 and the Tuolaishan fault, it is believed that the historical seismicity of the tectonic belt as a whole has a trend of continuous westward development, but there is an existing trend between the Hala Lake and the Tuolaishan Mountain. There is a more obvious seismic gap, so it is inferred that the future strong earthquake risk of the Tuoleishan Mountain fault is likely to increase.
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Key words:
- Menyuan /
- M6.9 earthquake /
- coseismic surface rupture /
- Qilian block /
- Haiyuan fault zone /
- Tuolaishan fault /
- earthquake hazard
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