维西—乔后断裂带的深部变形机制与构造活动特征  

Deep deformation mechanism and active tectonic along the Weixi-Qiaohou fault zone

作　　者：王一咪 徐龙辉 杨海燕[1] 金明培[3] WANG YiMi;XU LongHui;YANG HaiYan;JIN MingPei(Department of Geophysics,Yunnan University,Kunming 650091,China;Guangzhou Nanyue Seismic Engineering Survey Co.,Ltd.,Guangzhou 510070,China;Yunnan Earthquake Agency,Kunming 650224,China)

机构地区：[1]云南大学地球物理系,昆明650091 [2]广州南粤地震工程勘察有限公司,广州510070 [3]云南省地震局,昆明650224

出　　处：《地球物理学报》2023年第3期1070-1085,共16页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(42174064,41964002);国家重点研发计划子专题(2018YFC150330303)共同资助。

摘　　要：维西—乔后断裂是滇西地区一条典型的活动断裂,沿该断裂历史上多次发生过中强震,周边地区地壳变形强烈.地震各向异性是了解地球内部变形方式的重要手段,Moho面P-to-S转换波(Pms)的到时为探测具有水平对称轴的地壳各向异性提供了一种有力的诊断工具.本文利用大理及周边地区的68个宽频地震台站记录的远震三分量波形提取P波接收函数,并从叠加的P波接收函数里拾取不同后方位角对应的Pms震相到时,用网格搜索方法拟合该到时以获取地壳各向异性参数.获得的59个Pms震相的分裂参数表明,Pms分裂时间在0.06±0.06 s到0.97±0.10 s之间,平均值为0.50±0.07 s.优势快波偏振方向为SE-NW,地壳变形总体受控于区域的走滑运动.然而,在漾濞县及周边地区,快波偏振方向变为SW-NE,本文认为这主要由下地壳软弱物质向西南流动所致,同时也是导致维西—乔后断裂南段表现出正断层活动特征的原因.The Weixi-Qiaohou fault is a typical active fault in western Yunnan along which many moderate and strong earthquakes occurred and the crust experienced strong deformation. The arrival times of the converted P-to-S phase at the Moho(Pms) provide a powerful diagnostic tool to detect seismic anisotropy of the crust with a horizontal axis of symmetry and investigate the deformation of the Earth′s interior. With this purpose, we computed P-wave receiver functions from 3-component teleseismic waveforms recorded at 68 broadband seismic stations deployed in the Dali region, which were then moveout corrected to a reference epicentral distance of 67°. We then picked up the Pms phase arrival times of the stacked trace at each station and fit the Pms arrival times to measure crustal anisotropy using the grid-search method. Thus, we obtained a total of 59 Pms wave splitting parameters that show that the delay times between fast and slow waves range from 0.06±0.06 s to 0.97±0.10 s, being the average delay time of 0.50±0.07 s. The dominant fast-wave polarization direction is SE-NW, and crustal deformation is generally controlled by regional strike-slip movement. However, the dominant fast polarization direction changes to SW-NE in Yangbi and the adjacent region, a feature we attribute to the variation to the southwestward lower-crust flow, which is why normal faulting occurred in the south segment of the Weixi-Qiaohou fault.

关 键 词：P波接收函数 地壳各向异性 Pms分裂 方位叠加 下地壳流 

分 类 号：P315[天文地球—地震学]