新疆天山中段的震源机制解与构造应力场特征分析

doi:10.3969/j.issn.0253-4967.2020.03.004

摘要/Abstract

摘要： 文中收集了新疆测震台网2009-2018年记录的492个M_S2.5以上的地震事件, 以M_S=3.5为界, 分别用CAP方法和FOCEMEC程序计算其震源机制解, 并收集了GCMT记录的该区域历史地震事件的震源机制解结果。按照全球应力图分类标准对计算得到的震源机制解数据进行分类, 发现区域内中强地震主要以逆冲型为主, 兼有一定的走滑分量。采用阻尼区域应力场反演方法获取新疆天山中段的构造应力场空间分布特征, 结果表明研究区内最大主压应力轴由西向东呈扇形旋转, 自西段的NW向逐渐转为NE向, 仰角近水平, 最大主张应力轴近EW向, 仰角近直立。受喀什河断裂、那拉提断裂、博阿断裂、准噶尔南缘断裂和北轮台断裂等大型断裂带的影响, 局部区域应力场呈现出复杂的多样性。在帕米尔和塔里木块体持续向N挤压的影响下, 天山整体被挤压缩短, 但由南向北、由西向东缩短速率逐渐降低, 应力形因子自西向东逐渐增大, 且中间主压应力轴由偏压缩成分转为偏拉张成分。研究区南侧最大主压应力轴方向为N15°E, 而北侧则为近SN向, 这与塔里木块体的顺时针旋转有直接关联。区内近期发生的2次M_S6.6地震均造成区域应力场的逆时针旋转, 震后应力场与主震震源机制解趋于一致。

关键词: 新疆天山中段, 震源机制解, 构造应力场, 盆山结合带

Abstract: The middle part of the Tianshan Mountains in Xinjiang is located in the north-central part of the Tianshan orogenic belt, between the rigid Tarim Basin and Junggar Basin. It is one of the regions with frequent deformation and strong earthquake activities. In this paper, 492 M_S>2.5 earthquake events recorded by Xinjiang seismograph network from 2009 to 2018 were collected. The M_S3.5 earthquake was taken as the boundary, the focal mechanism solutions of the earthquake events in this region were calculated by CAP method and FOCEMEC method respectively. At the same time the focal mechanism solutions of GCMT recorded historical earthquake events in this region were also collected. According to the global stress map classification standard, the moderate-strong earthquakes in the region are mainly dominated by thrust with a certain slip component, which are distributed near the combined belts of the Tarim Basin, Junggar Basin, Turpan Basin and Yili Basin with Tianshan Mountains. The thrust component decreases from south to north, while the strike-slip component increases. The spatial distribution characteristics of the tectonic stress field in the middle section of the Tianshan Mountains in Xinjiang are obtained by using the damped regional-scale stress field inversion method. The maximum principal compressive stress in axis the study area rotated in a fan shape from west to east, the NW direction in the western section gradually shifted to NE direction, its elevation angle is nearly horizontal, in the state of near horizontal compression. The minimum principal compressive stress axis is nearly EW, and the elevation angle is nearly vertical. Influenced by large fault zones such as Kashi River, Bolhinur, Nalati, Fukang, the southern margin of the Junggar and the north Beiluntai, the local regional stress field presents complex diversity. Under the influence of the northward extrusion of Pamir and Tarim blocks, the whole Tianshan is shortened by compression, but its shortening rate decreases from south to north and from west to east, the stress shape factor increases gradually from west to east, the intermediate principal compressive stress axis exhibits a change in compression to extension. There are some differences in the characteristics of tectonic stress field between the north and south of Tianshan Mountains. The regional maximum principal compressive stress axis is 15° north by east on the south side, while it is nearly NS on the north side. The deformation of the Tianshan Mountains and the two basins on both sides is obviously larger than that in the inside of the mountain. Changes in the crustal shortening rate caused by the rotation of the rigid Tarim block and Junggar block to the relatively soft Tianshan block, as well as the uplifts of Borokonu and Bogda Mountains, the comprehensive influence of the material westward expansion constitute the stress field distribution characteristics of the north and south sides of the middle section of Tianshan Mountains. The recent two M_S6.6 earthquakes in the region caused the regional stress field to rotate counterclockwise. The post-earthquake stress field and the main source focal mechanism solution tend to be consistent. The seismic activity in the study area is week in the south and strong in the north. The focal depth is about 20km. Most strike-slip earthquakes occur near the junction belt of the Tianshan and Junggar Basin.

Key words: middle section of Tianshan Mountains, focal mechanism solution, tectonic stress field, basin-range junction belt

中图分类号:

P315.2

张志斌, 赵晓成, 任林. 新疆天山中段的震源机制解与构造应力场特征分析[J]. 地震地质, 2020, 42(3): 595-611.

ZHANG Zhi-bin ZHAO Xiao-cheng REN Lin. FOCAL MECHANISM SOLUTION AND TECTONIC STRESS FIELD CHARACTERISTICS OF THE MIDDLE TIANSHAN MOUNTAINS, XINJIANG[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(3): 595-611.

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