通州—三河地区沉积层高分辨率三维S波速度结构和径向各向异性  

High resolution 3D S-wave velocity structure and radial anisotropy of the sedimentary layer around Tongzhou-Sanhe area

作　　者：冯宣政 鲁来玉[1] 秦彤威 张友源 丁志峰[1] FENG XuanZheng;LU LaiYu;QIN TongWei;ZHANG YouYuan;DING ZhiFeng(Institution 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：《地球物理学报》2024年第5期1797-1818,共22页Chinese Journal of Geophysics

基　　金：国家自然科学基金地震联合基金(U1839209);国家重点研发计划(2017YFC1500200)共同资助.

摘　　要：北京大都市区位于冀中凹陷与太行山隆起和燕山褶皱带的交汇区,区内被第四系松软沉积层覆盖,历史和现今的地震活动性表明,其面临潜在的巨震风险.地震风险评估和强地面运动模拟依赖准确的沉积层三维S波速度模型.本文基于布设在通州—三河地区前所未有的密集台阵数据,构建了该区域高分辨率三维S波速度结构和径向各向异性模型.首先将919个台站组成的密集台阵划分为若干子台阵,利用修正的背景噪声聚束分析方法,提取各个子台阵的Love波频散曲线,通过深度反演构建了通州—三河地区三维SH波速度模型.结合由基阶和一阶Rayleigh波模式反演构建的三维SV波速度模型,获得了台阵下方的径向各向异性模型.模型显示,大兴断裂在穿过牛堡屯之后,继续向北东向延伸约20 km.大兴凸起以大兴断裂为界,表现出明显不同的构造特征和沉积过程.断裂的北西侧第四系沉积层较浅,推测约为100~400 m;断裂的南东侧第四系沉积层厚度横向变化较大,发育夏垫凹陷和甘棠凹陷.沉积盆地径向各向异性的幅度可达±20%,地表约0~60 m范围有一较强的负径向各向异性(VSH<VSV)覆盖层,推测与该地区垂直地裂缝发育有关.正的径向各向异性(VSH>VSV)是沉积作用造成的水平层序排列的沉积分层的反映.Beijing metropolitan area,which is covered by the Quaternary soft sedimentary layer,is located in the transition region around Jizhong Depression,Taihangshan Uplift and Yanshan Fold Belt.The seismicity shows that this area is at a risk of the significant earthquake.Seismic risk assessment and strong ground motion simulation rely on accurate 3D S-wave velocity model of the sedimentary layer.Based on the data from the unprecedented dense array deployed in Tongzhou area(sub-center of Beijing),a high-resolution 3D S-wave velocity structure and the radial anisotropy characteristics under the array are studied in this paper.We first divide the dense array consisting of 919 stations into 1485 subarrays.The Modified Cross-correlation Beamforming(MCBF)is used to extract the fundamental mode dispersion curves of Love wave for each subarray.The 3D high-resolution SH-wave velocity structure is then obtained by depth inversion.Combing with the 3D SV-wave velocity structure constructed by fundamental and the first overtone of Rayleigh wave,the radial anisotropy model under the array is built.The model shows that the Daxing Fault extends toward to NE direction after passing through Niubaotun.Bounded by the Daxing Fault,the Daxing High shows different characteristics and sedimentary process.On the northwest of the fault,the shallow Quaternary sedimentary layer with 100~400 m thickness is inferred.Xiadian and Gantang sags are developed on the southeast of the fault,where the thickness of the Quaternary sedimentary layer varies greatly.The radial anisotropy of the sedimentary basin can reach±20%.Near the surface,a covering layer shows a strong negative anisotropy(VSH<VSV)within 0~60 m,which may relate to the development of vertical cracks in this area.Positive radial anisotropy(VSH>VSV)is the reflection of sedimentary stratification of horizontal sequence arrangement due to sedimentation.

关 键 词：通州—三河地区 沉积层 密集台阵 聚束 三维S波速度结构 径向各向异性 

分 类 号：P315[天文地球—地震学]