滇西地区地壳三维精细结构成像与构造特征研究  

Three-dimensional fine structure imaging and tectonic characteristics of the crust in western Yunnan

作　　者：马永 张海江[2] 高磊 宋程 毕金孟 高也[1] MA Yong;ZHANG HaiJiang;GAO Lei;SONG Cheng;BI JinMeng;GAO Ye(Tianjin Earthquake Agency,Tianjin 300201,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]天津市地震局,天津300201 [2]中国科学技术大学地球和空间科学学院,合肥230026 [3]中国地质科学院,北京100037

出　　处：《地球物理学报》2023年第9期3674-3691,共18页Chinese Journal of Geophysics

基　　金：中国地震局三结合项目(3JH-202302019);天津市地震局科研项目(Zd202304)共同资助。

摘　　要：利用滇西及周边地区中国地震台网固定台站,中国地震局地球物理研究所和中国科学院地质与地球物理研究所的临时密集台阵的地震观测数据,使用具有一致性约束的双差地震层析成像方法,联合反演了滇西地区50 km以上深度VP、VS和VP/VS的三维精细结构模型.结果显示,在本研究区域范围内,地震主要集中在高速体的薄弱区域或高低速体过渡带偏向高速体的一侧,空间分布与速度结构之间表现出了很好的对应关系.低速异常体的分布情况非常复杂,受断裂构造限制十分明显,最大控制深度甚至达到了上地幔顶部.本文的地壳结构模型显示,滇西地区的莫霍面深度东西向变化幅度较小,而北南向由深变浅,且起伏变化较大,最深处大于55 km,最浅处约为29 km.波速比存在明显的壳幔边界转换带,在地壳内部变化范围为1.5~1.9,在上地幔顶部均在1.9~2.1之间,且与莫霍面的变化趋势一致.在腾冲火山区下方存在早期火山通道内冷却固结的岩浆侵入体或难以挥发的高密度残留体表现的高速体、尚未固结的岩浆囊或部分熔融物质的低速异常体和延伸至上地幔顶部的热流通道.大理地区存在北南向低速异常条带,推测可能为青藏高原下方向南运移的地壳物质,在区域构造应力作用下,促使在高低速异常体的转换区出现频繁的地震活动.龙陵、澜沧和耿马的4次7.0级以上强震虽然相距较远,但是它们具有相同的发震结构和孕震环境.模型结果可为分析滇西更多重点区域的深部构造背景提供精细的地壳结构数据支持.This paper used the seismic data from the fixed stations of the China Earthquake Networks Center,the temporary stations of the Institute of Geophysics,CEA and the Institute of Geology and Geophysics,CAS in western Yunnan and its surrounding areas to invert the three-dimensional fine structure models of VP,VS and VP/VS at depths of less than 50 km in western Yunnan by the consistency constrained double-difference tomography method.The results show that earthquakes are mainly concentrated in the weak area of the high-speed body or the transition zone of the high-low-velocity body is biased to the high-speed body,with good correspondence between the spatial distribution and the velocity structure.The distribution of low-velocity anomalous bodies is very complicated and restricted by fault structure,since the maximum control depth even reaches the top of the upper mantle.The crustal structure model shows that the depth of the Moho surface in western Yunnan varies little in the east-west direction,which it changes from deep to shallow in north-south direction with huge fluctuations.The deepest part is greater than 55 km,and the shallowest part is about 29 km.There is an obvious transition zone at the crust-mantle boundary,ranging from 1.5 to 1.9 in the inner crust and 1.9 to 2.1 at the top of the upper mantle,which is consistent with the variation trend of the Moho surface.Under the Tengchong volcanic area,there are high-velocity bodies represented by cooling and consolidated magmatic intrusions or unvolatilized high-density residues in the early volcanic channels,unconsolidated magma capsules or low speed abnormal bodies of molten materials,and heat flow channels extending to the top of the upper mantle.There are low-velocity anomalous bands in the North-South direction in the Dali area,which may be the crustal material migrating southward in the lower Tibetan Plateau.Under the action of regional tectonic stress,frequent seismic activity occurs in the transition zone of high and low velocity anomalies.Although the fo

关 键 词：滇西地区 双差层析成像 联合反演 速度结构 构造特征 

分 类 号：P315[天文地球—地震学]