麦宿断裂地震地表破裂带的发震构造分析  

Seismogenic structure of the earthquake surface rupture zone along the Maisu fault

作　　者：吴羿锋 唐方头[1] 姜旭东[1] Wu Yifeng;Tang Fangtou;Jiang Xudong(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China)

机构地区：[1]中国地震局地球物理研究所,北京100081

出　　处：《地震学报》2024年第5期751-766,共16页Acta Seismologica Sinica

基　　金：中国地震局地球物理研究所基本科研业务费专项(DQJB20B22);青藏二次科考专项(2019QZKK0708)共同资助

摘　　要：野外地质调查发现金沙江断裂带北段麦宿断裂附近发育长约50 km的地震地表破裂带,其最大垂直位移为2 m。基于该地震地表破裂带周围架设的密集地震台阵于2020年12月至2022年7月期间记录到的连续波形数据,采用双差定位方法对(31.55°N—31.85°N,98.31°E—98.98°E)区域内的578个地震事件进行定位,并利用基于P波初动的HASH方法对定位得到的地震事件进行震源机制解反演,获得了37组震源机制解,最后使用基于震源机制解的阻尼区域应力场反演方法对研究区域的应力环境进行了分析。精定位结果显示:研究区内沿地震地表破裂带分布着一条长约40 km的WNW−ESE向地震密集条带,震源密集分布在3—10 km深度范围内,深度剖面向北陡倾;同时还存在一条长约30 km的NNW−SSE向地震密集条带,震源密集分布在3—11 km深度范围内,深度剖面向西陡倾。震源机制解结果显示,研究区内地震的震源机制解以走滑型为主,占所获震源机制解的51.4%,同时也存在少量逆断型和正断型。震源机制解P轴的优势方位为近NW−SE向,与最大主压应力σ1方向323°相近。P轴、T轴、最大主压应力σ1以及最小主压应力σ3的倾角总体上较小,表明研究区内应力处于近NW−SE向的水平挤压状态;应力结构为走滑型,与地震定位和震源机制解结果相同;应力形因子R=0.57,表明最大主压应力σ1、中间主压应力σ2和最小主压应力σ3的本征值基本呈等差数列排列,其中σ1和σ3均为确定值。WNW−ESE向的地震密集条带具右旋走滑兼有正断和逆断分量,NNW−SSE向的地震密集条带具左旋走滑特征,表现为共轭断层特征。综合认为研究区曾发生过一次M>7.0地震,近NW−SE向水平挤压的应力状态与北部NW−SE向甘孜—玉树—鲜水河断裂带强烈左旋走滑有关。Field geological survey revealed the presence of an earthquake surface rupture zone 50 km long near the Maisu fault in the northern segment of the Jinshajiang fault zone,with a maximum vertical offset of 2 m.Based on the continuous waveform data of a dense seismic array set up around the rupture zone from December 2020 to July 2022,578 seismic events in the area of 31.55°N−31.85°N and 98.31°E−98.98°E were located by using the double-difference location method.The obtained seismic events were then analyzed using the HASH method based on P-wave initial motion to invert the focal mechanisms,and 37 focal mechanism solutions were acquired.The stress state of the study area was further analyzed by using the damped region-scale stress inversions method based on the focal mechanism solutions.The precise location results show that within the study area,there is a seismic belt 40 km long oriented WNW−ESE along the earthquake surface rupture zone,with focal depths clustered in the range of 3−10 km,and the depth profile steeply dips to the north.Moreover,there is another belt 30 km long oriented NNW−SSE,with focal depths concentrated at 3−11 km,dipping to the west.The results of focal mechanism solutions indicate that source mechanisms in this area are mostly strike-sip,accounting for 51.4%of the total.In addition,there are also a small number of reverse and normal fault mechanisms.The dominant azimuth of the P-axis of the focal mechanism solution is nearly NW−SE,which is similar to the direction of the maximum principal compressive stressσ1 at 323°.The overall dips of the P-axes,T-axes,maximum compressive stressσ1,and minimum compressive stressσ3 are small,suggesting that it is under an NW-SE oriented horizontal compressive stress regime.The stress structure is strike-slip,consistent with the earthquake location and focal mechanism solution results.The stress factor(R=0.57)indicates that the maximum compressive stressσ1,the intermediate compressive stressσ2 and the minimum compressive stressσ3 are b

关 键 词：麦宿断裂 地表破裂带 地震定位 震源机制解 发震构造 

分 类 号：P315.5[天文地球—地震学]