王怀富^1,2,,
吴建平^1,,,
周仕勇²,
房立华¹,
王未来¹,
刘雅宁¹
1. 中国地震局地球物理研究所, 北京 100081
2. 北京大学理论与应用地球物理研究所, 北京 100871

基金项目: 国家重点研发计划项目（2018YFC1503400）资助和国家自然科学基金项目（41374097，41774067）资助


详细信息

作者简介: 王怀富, 男, 1990年生, 固体地球物理学专业博士研究生.E-mail:wanghf@cea-igp.ac.cn

通讯作者: 吴建平, 男, 1963年生, 研究员, 博士生导师, 主要从事地震学与地球内部物理研究.E-mail:wjpwu@cea-igp.ac.cn

中图分类号: P315

收稿日期:2019-03-14
修回日期:2019-11-13
上线日期:2020-03-05

Rayleigh wave azimuthal anisotropy in the Southeastern Tibetan Plateau from Eikonal tomography

WANG HuaiFu^1,2,,
WU JianPing^1,,,
ZHOU ShiYong²,
FANG LiHua¹,
WANG WeiLai¹,
LIU YaNing¹
1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
2. Institute of Theoretical and Applied Geophysics, Peking University, Beijing 100871, China


More Information

Corresponding author: WU JianPing,E-mail:wjpwu@cea-igp.ac.cn

MSC: P315

--> Received Date: 14 March 2019
Revised Date: 13 November 2019
Available Online: 05 March 2020


摘要
摘要:青藏高原东南缘作为高原物质侧向挤出的前沿地带，是研究岩石圈变形机制、高原物质侧向逃逸和深部动力学等科学问题的关键地区之一.本文利用研究区内540个宽频带流动地震台站记录的远震面波资料，基于程函方程面波层析成像方法获得了青藏高原东南缘周期14~80 s瑞利面波相速度和方位各向异性分布图像.结果显示：14~20 s周期内，面波方位各向异性分布与断裂带的走向和最大主压应力的方向密切相关，可能受到了断裂带和区域构造应力场的共同作用.川滇菱形块体的北部次级块体及丽江—小金河断裂带附近随着面波周期的增加，各向异性快波方向从NS向逐步转变为NE-SW方向，并与断裂带大致平行，而其以南的攀枝花附近表现为高相速度和弱各向异性的特征.我们推测，在川滇菱形块体北部存在明显的下地壳流，流动方向与块体向南的挤出方向基本一致，该地壳流受到攀枝花附近的高速、高强度坚硬块体阻挡，其前缘向西南方向流动.川滇菱形块体中部地区由于坚硬块体的存在，下地壳没有明显的通道流.在红河断裂以西地区，30~60 s周期范围的面波各向异性快波方向和红河断裂大致平行，推测可能与渐新世至中新世早期印支地块向南东方向的挤出密切相关.研究区东北部，四川盆地南缘地壳各向异性以NE-SW和NEE-SWW向为主与SKS快波方向明显不同，推测主要与该地区地壳的早期构造变形有关同时也说明SKS各向异性主要来自上地幔介质；在研究区南部104°E以西的中长周期面波各向异性方向与SKS分裂研究获得的近EW快波方向基本一致，但在104°E以东地区面波各向异性较弱且快波方向与SKS的观测结果存在明显差异，我们推测东部SKS各向异性来源深度至少在150 km以下.
关键词: 程函方程/
面波相速度/
方位各向异性/
剪切波分裂

Abstract:As the frontier zone for lateral extrusion of plateau material, the southeastern margin of the Tibetan Plateau is one of the key areas for studying lithospheric deformation, plateau material lateral escape and deep dynamics. Based on data of 540 broadband digital seismic stations in the study area, we obtain the Rayleigh wave phase velocity and azimuthal anisotropy distribution images at 14~80 s periods of the southeastern margin of the Tibetan Plateau by Eikonal surface wave tomography. The results show that the azimuthal anisotropy distribution of the surface waves at 14~20 s period is closely related to the direction of the fault zone and the direction of the maximum principal compressive stress, which may be affected by the fault zones and the regional tectonic stress field. With the increase of the surface wave period near the northern sub-block of the Sichuan-Yunnan diamond block and Lijiang-Xiaojinhe fault zone, the anisotropic fast wave direction gradually changes from NS to NE-SW and is roughly parallel to the fault zone. However, the vicinity of Panzhihua is characterized by high velocity and weak anisotropy. We speculate that there is a lower crust flow in the northern part of the Sichuan-Yunnan active block, and the flow direction is basically the same as the southward extrusion direction of the block. The crustal flow is blocked by the high-speed, high-strength block near Panzhihua in the middle of the Sichuan-Yunnan block and its leading edge flows to the southwest. There is no obvious channel flow in the lower crust in the central region due to the presence of hard blocks. In the west area of the Red River fault, the fast wave direction of surface wave anisotropy at the period of 30~60 s is roughly parallel to the Red River fault, which is speculated to be closely related to the extrusion of the Indosinian block to SE from the Oligocene to the Early Miocene. In the northeast of the study area, the crustal anisotropy of the southern margin of the Sichuan basin is dominated by NE-SW and NEE-SWW, which are obviously different from the SKS fast wave directions. It is speculated that the anisotropy is mainly related to the early tectonic deformation of the crust in this area, which also indicates that the SKS anisotropy mainly comes from the upper mantle. The anisotropic direction of the mid-long period surface waves in the west of 104°E south of the study area is basically consistent with the nearly EW fast wave direction obtained by SKS splitting research. But the surface wave anisotropy is weaker in the east of 104°E and the fast wave direction is significantly different from SKS splitting. We speculate that the SKS anisotropy source depth in the east is at least below 150 km.
Key words:Eikonal equation/
Rayleigh Wave phase velocity/
Azimuthal anisotropy/
Shear wave splitting



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