摘要
利用2002-2003年中国地震局地质研究所台阵实验室以唐山大震区为中心布设的40个流动宽频带地震台站和首都圈数字台网的33个宽频带台站的远震数据,采用接收函数非线性反演方法得到其中72个宽频带台站下方60 km深度范围内的S波速度结构.根据得到的各台站下方地壳上地幔的S波速度结构,并综合刘启元等(1997)用接收函数非线性反演方法得到的延怀盆地15个宽频带流动台站下方的地壳上地幔S波速度结构模型,给出了39°N-41°N ,114°E-7.19. 5°E区域内沿不同走向、不同深度S波速度分布.由于综合了利用首都圈数字地震台网的宽频带台站以及流动地震台阵的观测数据,本文给出了较前人同类研究空间分辨率更好的结果.结果表明:(1)研究区的速度结构,特别是怀来以东的速度结构十分复杂.在10-20 km深度范围内,研究区地壳具有高速和低速异常块体的交错结构.研究区中上地壳速度结构主要被与张渤地震带大体重合的NW向高速条带和穿越唐山大震区的NE向高速条带所控制,而其中下地壳的速度结构主要为延怀一三河一唐山地区上地幔隆起所控制.(2)研究区内存在若干壳内S波低速体,它们主要分布在唐山,三河及延怀盆地等地区.在这些地区,壳内低速体伴随着壳幔界面的隆起和上地幔顶部速度结构的横向变化.(3)地表断层分布与地壳速度结构分区有较好的相关性,表明断层对不同块体有明显的控制作用.其中,宝坻断裂,香河断裂和唐山断裂均为超壳断裂.(4)首都圈内大地震的分布与壳内低速体及上地幔顶部的速度结构有密切关系.对于唐山大地震的成因,仅考虑板块作用引起的水平应力场是不够的,有必要充分重视由于上地幔变形引起的地壳垂直变形和上地幔物质侵人造成的热效应.
In this study we use the nonlinear inversion method of receiver functions to investigate the S-wave velocity structure of the crust and upper mantle beneath the capital circle region from teleseismic broadband waveform data recorded at 40 movable stations deployed over the Tangshan earthquake region in 2002-2003 by the Laboratory of Lithospheric Seismic Array, Institute of Geology, China Earthquake Administration and recorded at 33 permanent stations of the Digital Seismic Network in the Capital Circle. Based on these results, combining the S-wave velocity structures of the crust and upper mantle beneath 15 moveable broadband seismic stations over the Yanhuai basin by Liu et al. （1997）, we present the S-wave velocity distribution along the profiles with different azimuths and horizontal distributions at different depths over the region of 39°～41°N and 114°-119.5°E. Our results show the crustal velocity structure with spatial resolution higher than former studies due to using the data recorded by permanent and movable stations simultaneously. Our results show： （1） the S-wave velocity structure of the crust and upper mantle down to 60 km deep beneath our research area, especially to the east of the Yanhuai basin, is quite complicated. The crust at depth of 10-20 km has an interlaced structure of alternating high- and low-velocity anomalies. The upper and middle crust is dominated by the NE-direction high-velocity anomalous region parallel with the Zhangjiakou-Bohai seismic zone as well as the belt across the Tangshan earthquake region, while the lower crust is dominated by the uplift of the upper mantle beneath the Yanhuai, Sanhe and Tangshan region. （2） beneath our research region exist several S-wave low velocity bodies in the crust, which are mainly distributed in the Tangshan, Sanhe, Yanhuai region, accompanied by the uplift of the crust-mantle boundary and lateral variations of the upper mantle velocity structure. （3） the fault system on the surface is well correlated with the crustal velocity structure, suggesting that the different crustal blocks are dominated by the faults. Among them, the Baodi fault, Xianghe fault, and Tangshan fault are through the crust. （4） large earthquakes in the capital circle region are related closely to the low velocity bodies in the crust and the velocity structure at the top of the upper mantle. As for the genesis of the Tangshan earthquake, it will not be sufficient only considering the horizontal stress field caused by the plate tectonics and it becomes also important to pay much attention to the vertical crustal deformation caused by the upper mantle uplift as well as the thermal effects caused by the upper mantle material intrusion.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2009年第10期2472-2482,共11页
Chinese Journal of Geophysics
基金
国家重大基础研究计划(973)(2004CB418402)资助
关键词
首都圈
接收函数反演
流动地震台阵
地壳上地慢S波速度结构
Capital Circle region
Receiver function inversion
Movable seismic array
S-wave velocity structure of the crust and upper mantle structure
