摘要
利用海原弧形构造区及周围区域地震台网1970—2015年期间记录的天然地震到时数据,采用双差地震层析成像方法对构造区地壳三维速度结构与地震震源位置进行联合反演,获得了高分辨率的三维VP、VS以及VP/VS模型,分析讨论了速度、波速比分布与强震发生以及断裂等之间的关系.结果显示:研究区域内地震主要沿断裂呈弧状展布,速度在横向分布上具有较大的差异,波速比变化范围为1.60~1.80,平均值约为1.70.大型断裂诸如海原—六盘山断裂带、青铜峡—固原断裂带等位于高速与低速的过渡带,断裂两侧地震波速差异较大.研究区内历史强震多处于高低速过渡区域,海原强震下方下地壳存在低速、高导薄弱层(25~30 km深度),推测原因主要为流体作用所致.依据相对较低的速度与波速比分布推测研究区地壳主要组成成分为酸性的长英质.速度剖面显示地壳可分为上、下两层,上、下地壳厚度变化由西南向东北逐渐减薄,减薄幅度相近;结合前人研究结果推测构造区地壳增厚模式可能主要为上、下地壳共同增厚.
We collected first arrivals of P and S waves recorded by regional seismic stations in the Haiyuan arcuate tectonic zone and its adjacent regions from 1970—2015.Velocity structure and hypocenter parameter were inverted jointly by Double-difference tomography(Tomodd),and a high resolution three-dimensional(3D)P and S wave velocity(VP、VS and VP/VS)model of the crust beneath the Haiyuan arcuate tectonic zone was constructed.The relationship between distribution of velocity,VP/VS ratio and strong earthquakes and faults is discussed.The tomography results reveal earthquakes are mainly distributed along faults,and the velocity has a great difference in the lateral distribution in the study area.The VP/VS ratio varies from 1.60 to 1.80,1.70 on average.Large faults such as the Haiyuan-Liupanshan fault zone and Qingtongxia-Guyuan fault zone are located in the transition zone of high and low velocity,and the velocities across the fault zones exhibit a sharp contrast.Most of historical major earthquakes in the study area mainly occurred at the boundaries of low and high velocity.At 25~30 km depth,a weak layer with low velocity and high conductivity is observed in the lower crust below the 1920 Haiyuan great earthquake,which is presumably associated with fluid.The relatively lower velocity and VP/VS ratio may indicate that the composition of the crust in the study area is mainly acidic felsic.The velocity profiles show that the crust can be divided into upper and lower layers,of which the thicknesses gradually reduces from southwest to northeast,and the extents of thinning are similar.Coupled with previous studies,we propose that the joint thickening of the upper and lower crust is the main deformation mechanism as the crustal thickening mode in the study area.
作者
莘海亮
曾宪伟
康敏
高级
XIN HaiLiang;ZENG XianWei;KANG Min;GAO Ji(Geophysical Exploration Center,China Earthquake Administration,Zhengzhou 450002,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Earthquake Agency of Ningxia Hui Autonomous Region,Yinchuan 750001,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第3期897-914,共18页
Chinese Journal of Geophysics
基金
中国地震局地震科技星火计划项目（XH16051Y,XH18053Y）
国家自然科学基金项目（41704058）联合资助
关键词
海原弧形构造区
双差层析成像
地壳速度结构
波速比
Haiyuan arcuate tectonic zone
Double-difference tomography
Crustal velocity structure
V P/V S ratio
