基于背景噪声成像研究海原—六盘山地区地壳三维速度结构及其构造意义  

Three-dimensional crustal velocity structure and tectonic implication of the Haiyuan-Liupan Mountain area based on ambient noise tomography

作　　者：李蒙亚 曾宪伟[1] 姚华建[2] 冯吉坤[2] 李新艳[1] 杨硕 LI MengYa;ZENG XianWei;YAO HuaJian;FENG JiKun;LI XinYan;YANG Shuo(Earthquake Agency of Ningxia Hui Autonomous Region,Yinchuan 750001,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]宁夏回族自治区地震局,银川750001 [2]中国科学技术大学地球和空间科学学院,合肥230026

出　　处：《地球物理学报》2024年第12期4666-4680,共15页Chinese Journal of Geophysics

基　　金：宁夏自然科学基金项目(2022AAC03696,2023AAC03812);震情跟踪定向工作任务(2022010125)联合资助.

摘　　要：海原—六盘山地区地处青藏高原东北缘,是青藏块体东北向挤压的前缘地带,地质构造活动活跃,历史上曾发生过多次7级以上地震.但该区域已多年未发生6级以上强震,是一个具有发生强震危险性的地震空区.精细的速度结构能够为认识海原—六盘山地区的构造活动性和地震危险性提供帮助.本文以布设在该区域的50个流动台站和38个固定台站为基础,提取Rayleigh波相速度频散曲线,通过面波直接成像方法获得了研究区地壳三维精细横波速度结构,再结合区域2010年至2023年地震精定位的结果,得到以下认识:(1)研究区以海原—六盘山断裂为分界线,东西两侧结构差异显著.东侧鄂尔多斯块体浅部以大范围的低速沉积层为主,对应较低的地震活动性;西侧为高速异常,对应较高的地震活动性.(2)精定位结果显示,大部分地震发生在高低速异常体边界线上,分布特征与地表构造单元表现出较好的一致性.(3)六盘山和鄂尔多斯西缘靠近西秦岭北缘断裂带呈现明显的高速异常,推测该区域地处祁连造山带,反映了深部致密的基底结晶.(4)海原—六盘山地区的地壳厚度自南西向北东逐渐减薄,且在本研究区域的中下地壳未发现低速异常体“通道”.The Haiyuan-Liupan Mountain region,located on the northeastern edge of the Tibetan Plateau,is the frontal zone of the northeastern compression of the Tibetan block,characterized by active geological structures.Historically,this region has experienced several earthquakes with magnitudes exceeding 7.However,there have been no strong earthquakes of magnitude 6 or higher in many years in this area,making it a seismic gap with potential risks of strong earthquakes.Detailed velocity structures of the Haiyuan-Liupan Mountain region can help to understanding regional tectonic activity and seismic hazard.This study performed ambient noise tomography to obtain high-resolution three-dimensional crustal shear wave velocity structure,based on the continuous data from 50 temporary and 38 permanent seismic stations deployed in the study region.Combined with the precise earthquake relocation results from 2010 to 2023,several insights were obtained.(1)The study area,divided by the Haiyuan-Liupan Mountain fault,exhibits notable structural differences between its eastern and western sides.The eastern side,part of the Ordos Block,primarily consists of large area low-velocity sedimentary layers associated with lower seismic activity;whereas,the western side is featured by prominent high-velocity anomalies and higher seismic activity.(2)Precisely relocated earthquakes indicate that most earthquakes occur along the boundaries of high and low-velocity anomalies,with their distribution showing good consistency with surface tectonic units.(3)Near the northern margin of the Western Qinling fault zone,the Liupan Mountain and western edge of the Ordos display distinct high-velocity anomalies,suggesting that this area is part of the Qilian orogenic belt with dense crystalline basement at depth.(4)The crustal thickness in the Haiyuan-Liupan Mountain region gradually decreases from the southwest to the northeast,and no low-velocity“channels”were observed in the middle to lower crust within the study area.

关 键 词：青藏高原东北缘 背景噪声成像 地壳 海原—六盘山断裂带 地震活动性 

分 类 号：P315[天文地球—地震学]