固定台站与流动台阵资料揭示的青藏高原东北缘及邻区上地壳地震各向异性  

Seismic anisotropy of the upper crust in the northeastern border of the Tibetan Plateau and adjacent areas revealed by both permanent and temporary stations

作　　者：刘同振 高原[1] 夏新宇 李抒予 LIU TongZhen;GAO Yuan;XIA XinYu;LI ShuYu(Key Laboratory of Earthquake Prediction,Institute of Earthquake Forecasting,China Earthquake Administration,Beijing 100036,China;Center for Geophysical Survey,China Geological Survey,Langfang Hebei 065000,China)

机构地区：[1]中国地震局地震预测研究所(地震预测重点实验室),北京100036 [2]中国地质调查局地球物理调查中心,河北廊坊065000

出　　处：《地球物理学报》2025年第3期857-881,共25页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(42494863);中国地质调查局地质调查项目(DD20243193)共同资助。

摘　　要：利用甘肃、宁夏、陕西、四川和内蒙古固定地震台网(2018年10月至2021年11月)和中国地震局地震预测研究所布设的跨海原断裂带流动地震台阵(SACHY)部分台站(2012年11月至2014年10月)记录的近场小震波形资料,运用剪切波分裂系统分析方法(SAM),分析了青藏高原东北缘及邻区的上地壳各向异性特征.本研究对流动地震台阵采用微震识别技术,获得中国地震台网中心公布的地震目录里没有的许多微震事件,新增1.6倍剪切波分裂有效数据.结果表明,青藏高原东北缘快剪切波偏振方向主要有NE、NW及近EW向,呈现明显的分区特征.研究区可分为五个区域,其中海原断裂带及北侧银川地堑又分为两个子区.银川地堑周缘,台站快剪切波偏振方向为NE,与构造应力场有很好的一致性;海原断裂带附近台站的快剪切波偏振方向与断裂带走向大致平行;青藏块体东侧,台站快波方向为NW向,与主压应力方向及大地测量资料揭示的构造变形场一致;龙门山断裂带北段台站快剪切波偏振方向呈现NW和ENE向,受到区域构造应力场和断裂的共同作用;秦岭造山带邻区台站快剪切波偏振方向为近EW向,与震源机制揭示的构造应力方向吻合;渭河盆地周缘,台站快波方向为NE向,与华北块体主压应力方向一致.慢波时间延迟结果显示,在构造边界或大型断裂带局部地区呈现出强各向异性区,揭示出构造作用的差异性.结合区域已有的地球物理学研究结果,本文研究结果支持海原断裂带为青藏高原壳内物质北东向伸展的边界带.Utilizing the seismic data recorded by the permanent seismic networks in Gansu,Ningxia,Shaanxi,Sichuan,and Inner Mongolia(from October 2018 to November 2021),as well as some stations of the mobile seismic array(SACHY)deployed across the Haiyuan fault zone by the Institute of Earthquake Forecasting of China Earthquake Administration(from November 2012 to October 2014),we applied the shear-wave splitting analysis method(SAM)to investigate the upper crustal anisotropy beneath the northeastern margin of the Tibetan Plateau and its adjacent areas.For the temporary stations,we employed microseismic identification techniques to detect missing microseismicity not listed in the earthquake catalog published by the China Earthquake Network Center,increasing the shear-wave splitting data by 1.6 times.The results show that the fast shear-wave polarizations in the northeastern margin of the Tibetan Plateau are primarily in NE,NW,and nearly EW,indicating distinct spatial differences.We separated the study area into five sub-areas,with the Haiyuan fault zone and the north side of the Yinchuan graben further being sub-divided into two areas.Around the periphery of the Yinchuan graben,the polarization of fast shear waves is NE,which is consistent with the tectonic stress field.For the stations around the Haiyuan fault zone,the polarization of the fast shear waves is nearly parallel to the strike of the fault zone.At the eastern side of the Tibetan block,the polarization of the fast waves is NW,which is in agreement with the main compressive stress and crustal movement direction revealed by geodetic data.In the northern segment of the Longmenshan fault zone,the polarizations of fast shear waves are in NW and ENE respectively,influenced by the regional tectonic stress and the fault deformation.Adjacent to the Qinling orogenic belt,the fast shear-wave polarization is nearly EW,matching the tectonic stress direction revealed by the focal mechanism.Around the Weihe basin,the fast polarization is NE,consistent with the main compressive

关 键 词：青藏高原东北缘 剪切波分裂 上地壳各向异性 微震识别 应力 断裂 地壳变形 

分 类 号：P315[天文地球—地震学]