华北克拉通中西部及周边地区瑞利面波相速度方位各向异性  

Rayleigh wave phase velocity and azimuthal anisotropy in the central and western North China Craton and surrounding areas

作　　者：钟世军[1,2] 吴建平[1] 司政亚 ZHONG ShiJun;WU JianPing;SI ZhengYa(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Beijing Earthquake Agency,Beijing 100080,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]北京市地震局,北京100080

出　　处：《地球物理学报》2024年第8期2926-2945,共20页Chinese Journal of Geophysics

基　　金：国家自然科学基金(42174117);中国地震局地球物理研究所基本科研业务专项(DQJB23B22)资助。

摘　　要：利用“中国科学台阵探测”项目的密集流动台站以及区域固定台站的地震面波记录,采用程函面波成像方法,得到了华北克拉通中西部及周边地区14~100 s周期高分辨率的瑞利面波相速度方位各向异性分布图像.结果显示,鄂尔多斯块体内部中长周期(20~100 s)为大范围高速和弱各向异性分布特征,但在块体西南部区域各向异性明显增强,向东可一直延伸至108°E附近.我们认为,受青藏高原影响,鄂尔多斯块体西南部岩石圈已发生明显变形,高原扩张对鄂尔多斯块体的影响超出了止于六盘山逆冲推覆带的传统认识.在鄂尔多斯块体内部,长周期(80~100 s)的相速度显示高速区向中部和东南部区域收缩,各向异性强度在高速区外围明显增强,揭示了块体边界带的岩石圈在后期构造活动过程中已遭受不同程度的变形改造,厚度发生了不同程度的减薄.山西断陷带北部大同火山区附近,在20 s以上周期为显著低速异常,不同周期段各向异性存在明显差异,我们推测该区不同深度的各向异性差异与鄂尔多斯块体东北部岩石圈不同深度的几何形态以及青藏高原远程挤压效应有关.山西断陷带中南部区域,在20~60 s周期显示高速和近EW向快波方向,与鄂尔多斯块体中东部高速区具有较好的连续性,认为该区岩石圈仍保留部分原有华北克拉通岩石圈的属性.青藏高原东北缘地区不同周期相速度表现为明显的低速异常,快波方向呈现较为一致的NWW-SEE向分布特征,揭示了在高原下方壳幔介质变形连续一致,符合岩石圈垂直连贯变形模式.We have obtained high-resolution Rayleigh surface wave phase velocity and azimuthal anisotropy maps at periods of 14~100 s in the central and western North China Craton and its surrounding regions from Eikonal surface wave tomography.The surface wave data comes from the dense portable stations of ChinArray and permanent stations of China National Seismic Network.The results show that there exhibits a wide range of high-velocity and weak anisotropy in the Ordos Block at periods of 20~100 s,but the anisotropy is strong in the southwest of this block,and it can extends eastward to 108°E.The results indicate that the lithosphere has undergone significant deformation in the southwestern Ordos Block under the influence of the Tibetan Plateau.The influence of the plateau expansion on the Ordos Block is obviously beyond the Liupanshan thrust belt.The high-velocity anomaly shrinks to the central and southeastern regions in this block at the long periods(80~100 s),and the anisotropy is significantly stronger around the high-velocity region,which reveals that the boundary zones of Ordos Block have been subjected to different degrees of deformation and modification,and resulting in non-uniform lithospheric thinning.Datong volcanic field in the north of Shanxi Rift Zone is characterized by low velocity anomaly at periods of greater than 20 s,and the anisotropy shows significant difference at different periods.We speculate that this phenomenon is related to the geometry of lithosphere at different depths in the northeastern Ordos Block and the long-range compression effect from Tibetan Plateau.High-velocity and near E-W fast wave direction are shown at periods of 20~60 s in central and southern Shanxi Rift Zone,which consistent with that in the central and eastern Ordos Block.We speculate that the lithosphere still remains some properties of the ancient North China Craton in this region.In northeastern margin of the Tibetan Plateau,where dominated by prominent low-velocity anomaly and consistent NWW-SEE fast wave direction at

关 键 词：鄂尔多斯块体 山西断陷带 青藏高原东北缘 程函方程面波成像 相速度 快波方向 

分 类 号：P315[天文地球—地震学]