摘要
鄂尔多斯及邻区一直是研究活动地块间相互作用和物质运移的热点区域.青藏高原的扩展与鄂尔多斯地块内部及周缘的变形之间的耦合关系仍有待厘定.基于“中国地震科学台阵探测”项目的密集台阵和固定台网数据,本文利用区域地震全波形层析成像方法获得了研究区三维S波速度和径向各向异性结构,结果表明:鄂尔多斯地块存在以37°N为界的南北速度结构差异,南部的相对低速反映了较厚的地壳,与地形地貌相对应;鄂尔多斯西南缘在中、上地壳表现为负径向各向异性结构特征,S波速度扰动在中地壳呈显著的低速异常,延伸到鄂尔多斯西南部,该区域作为青藏高原扩展的前缘,速度结构特征反映了中地壳滑脱,上地壳缩短变形的地壳增厚模式;具有扩展早期构造变形特征的阿拉善地块南部呈相对低速,在上地壳表现为明显的负径向各向异性;鄂尔多斯东缘的山西断陷带存在南北速度结构差异,断陷带北部下地壳为低速异常,反映受地幔热物质改造的软弱物质堆积,断陷带中部则呈相对高速结构特征,推测其深部构造应力、应变环境比较稳定;负径向各向异性结构在南北地震带北段和山西断陷带浅部均有分布,为深入研究地震活动性与地壳速度结构的关系提供了波形成像证据.
The Ordos Block and its adjacent areas are not only the hot spots for studying the interaction between active blocks,but also the migration of materials between active blocks.However,the coupling relationship between the crustal deformation in and around the Ordos Block and the extension of the Tibetan Plateau remains to be determined.In this paper,based on the seismic data in the 20~40 s recorded by permanent stations from China National Seismic Network and mobile stations from ChinArray-Himalaya broadband seismic array,the three-dimensional S-wave velocity structure and radial anisotropy structure in the study area are obtained by using full-waveform tomography.The imaging results revealed that:There is a difference in velocity structure between the north and south part with 37°N as the boundary.The low-velocity feature of the southern Ordos reflects the thicker crust,which corresponds to the topography.The middle and upper crust in the southwest margins show negative radial anisotropy,in which the S-wave velocity perturbation in the middle crust is a significant low-velocity anomaly,extending to the southwest of the Ordos Block.This region is speculated to be the front edge of the expansion of the Tibetan Plateau.It is believed that the velocity structure characteristics reflect the crustal shortening model that detachment in the middle crust and thickening deformation in the upper crust underneath the southwest margins of the Ordos Block.The southern Alashan Block,which has the characteristics of early tectonic deformation during the expansion of the Tibetan Plateau,shows relatively low-velocity feature and obvious negative radial anisotropy in the upper crust.There is a difference in velocity structure between the north and south part of the Shanxi rift zone in the eastern margin of Ordos.The lower crust of the northern Shanxi rift zone shows low-velocity anomaly,reflecting the accumulation of weak materials under the influence of mantle thermal material transformation,while the central Shanxi rift zone is a relatively high-velocity structure,suggesting that the deep tectonic stress and strain environment is stable.In addition,the negative radial anisotropic structures are distributed in the northern section of The North-South Seismic Belt(NSSB)and the upper crust of the Shanxi rift zone,which provides waveform imaging evidence for further study of the relationship between seismicity and crustal velocity structure.
作者
杨镓文
侯卫生
陈九辉
李俊毅
郑文俊
YANG JiaWen;HOU WeiSheng;CHEN JiuHui;LI JunYi;ZHENG WenJun(School of Earth Sciences and Engineering,Sun Yat-Sen University,Guangdong Provincial Key Lab of Geodynamics and Geohazards,Zhuhai 519082,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,China;State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China)
出处
《地球物理学进展》
CSCD
北大核心
2024年第1期48-62,共15页
Progress in Geophysics
基金
国家重点研发计划(2017YFC1500103)
国家自然科学基金项目(41972302)联合资助.
