剪切波分裂揭示的华北克拉通中部造山带上地壳地震各向异性  

Upper crust seismic anisotropy in the central orogenic belt of North China Craton revealed by shear-wave splitting

作　　者：王想 高原[3] 吴鹏[4] 周依 王时 WANG Xiang;GAO Yuan;WU Peng;ZHOU Yi;WANG Shi(Hebei Hongshan National Observatory on Thick Sediments and Seismic Hazards,Xingtai Hebei 054000,China;Hebei Earthquake Agency,Shijiazhuang 050021,China;Institute of Earthquake Science,China Earthquake Administration,Beijing 100036,China;Handan Central Seismic Station,Handan Hebei 056001,China;Shijiazhuang Central Seismic Station,Shijiazhuang 050021,China)

机构地区：[1]河北红山巨厚沉积与地震灾害国家野外科学观测研究站,河北邢台054000 [2]河北省地震局,石家庄050021 [3]中国地震局地震预测研究所,北京100036 [4]邯郸地震监测中心站,河北邯郸056001 [5]石家庄监测中心站,石家庄050021

出　　处：《地球物理学报》2022年第7期2503-2517,共15页Chinese Journal of Geophysics

基　　金：中国地震科技星火计划(XH17007,XH21003Y);河北省地震局星火计划重点项目(DZ20170109002,DZ20180402056,DZ202108090114);河北“十三五”科技支撑项目(2018-130000-74-01-001627)共同资助。

摘　　要：利用布设在华北克拉通中部造山带的流动地震台网和区域固定地震台网的近场地震波形资料,获得55个台站、符合剪切波分裂分析的共计534条有效记录,得到每个台站下方的剪切波分裂参数(快剪切波偏振方向和慢剪切波时间延迟),展现了研究区上地壳各向异性分布特征.结果显示,华北克拉通中部造山带区域优势快波方向大致呈NE向,与华北区域背景主压应力方向近EW向有所差别,揭示出研究区内山西地堑与太行山隆起等形成的盆山构造对地壳结构的影响.台站优势快波方向主要平行于主压应力方向,或与断裂/构造走向一致,表明断裂与局部地质构造对各向异性的影响以及断裂构造与应力场的相互影响.山西地堑优势快波方向呈NE向,其中大同盆地离散性较大.山西地堑北端与张-渤地震带交汇区北侧优势快波方向呈WNW向,南侧呈NE向且离散较大.太行山隆起与华北盆地交汇区的优势快波方向同为NE向,第二优势快波方向近EW向,体现了华北地区的各向异性特征.山西地堑的时间延迟从南到北逐渐减少但变化不大,分区平均值最大相差0.2 ms·km^(-1).太行山隆起与华北盆地交汇区的时间延迟和山西地堑北端与张-渤地震带交汇区北侧相对较小,表明该区上地壳变形程度相对较小,可能与该区地震活动较强、难以积累更强的地壳变形有关.本研究还对该区域的地壳和上地幔的耦合问题进行了初步讨论,认为华北克拉通中部造山带的壳幔耦合关系不能用壳幔解耦或壳幔耦合进行简单描述.Using the near-field local seismic data from temporary and permanent seismic network in the central orogenic belt of the North China Craton,we obtain the anisotropic parameters at 55 stations by the shear-wave splitting(SWS)analysis from a total of 534 individual measurements.The results show that the polarization of fast shear-wave(PFS)at most stations is parallel to the direction of the regional compressive stress(EW),while it at some stations is consistent with the strike of fault or the trend of major geological structures,indicating that the anisotropic mechanism is influenced by faults,geological structure,and the regional compressive stress.The predominant PFS in Shanxi Graben is in NE direction.However,the PFS in the north of the intersection area of the Shanxi Graben and the Zhang-Bo Seismic Belt is in WNW orientation,but the rose diagram of PFS orientations in the south is complicated,with the predominant PFS in NE direction.The predominant PFS in the intersection of Taihang Mountain uplifting and North China Basin is in NE orientation,and the secondary dominant PFS is in nearly EW direction,reflecting the complex anisotropic characteristics in the North China.The time delay of the Shanxi Graben gradually decreases from south to north.The biggest difference between subzones is 0.2 ms·km^(-1).The time delay of the intersection area of Taihang Mountain uplifting and North China Basin,and the north of the intersection area of the Shanxi Graben and the Zhang-Bo Seismic Belt are relatively small,indicating that the upper crust deformation in this area is relatively weak and strong seismic activity is to the disadvantage of strain accumulation.Our results also suggest that the extent of crust-mantle coupling cannot be explained by the simple relationship of decouple or couple.

关 键 词：华北克拉通中部造山带 山西地堑 张家口—渤海地震带 剪切波分裂 上地壳各向异性 主压应力 快波偏振方向 慢波时间延迟 

分 类 号：P315[天文地球—地震学]