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以 2006年中国地震局地质研究所地震动力学国家重点实验室在川西地区(26°N～32°N,100°E～105°E)布设了由297台宽频带数字地震仪组成的流动观测台阵.利用该密集台阵29°N以北156个台站2007年1～12月份的地震环境噪声记录和互相关技术,我们得到了所有台站对的面波经验格林函数和瑞利波相速度频散曲线,并进一步反演得到了观测台阵下方2～35 s周期的瑞利波相速度分布图像.本文结果表明,观测台阵覆盖的川滇地块、松潘甘孜地块和四川盆地的地壳速度结构存在显著差异,具体表现为:(1)短周期(2～8 s)相速度分布与地表构造特征相吻合,作为川滇地块、松潘甘孜地块和四川盆地之间的边界断裂,龙门山断裂带和鲜水河断裂带对上述三个地块上地壳的速度结构具有明显的控制作用,四川盆地前陆低速特征表明相应区域存在较厚的(约10 km)沉积盖层;(2)中周期(12～18 s)相速度分布表明,川滇地块和松潘—甘孜地块中上地壳速度结构存在明显的不均匀横向变化,并形成了尺度不同且高、低速相间的分块结构,而四川盆地中地壳整体上已经表现出相对高速;(3)长周期(25～35 s)相速度分布表明,松潘甘孜地块,特别是川滇地块中下地壳表现为广泛的明显低速异常,意味着它们的中下地壳相对软弱,而四川盆地的中下地壳呈现整体性的相对高速,意味着四川盆地具有相对坚硬的中下地壳,并且以汶川地震的震中为界,龙门山断裂带的地壳结构显示了北段为高速异常,南段为低速异常的分段特征.
Based on the observation that there are 297 broadband digital seismographs in the western Sichuan region (26 ° N ~ 32 ° N, 100 ° E ~ 105 ° E) in 2006 by the State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration Using the seismic environment noise recording and cross-correlation techniques from 156 stations north of 29 ° N of this intensive array in January 2007 to December 2007, we obtain the empirical Green’s function and the Rayleigh waves Phase velocity dispersion curves were obtained and the Rayleigh wave phase velocity distribution images were obtained by inversion from 2 to 35 s below the observed array.The results of this paper show that the distributions of the Rayleigh wave velocities in the Sichuan-Yunnan block, the Songpan-Ganzi block and the Sichuan The velocity structure of the crust in the basin is significantly different. The specific manifestations are as follows: (1) The phase velocity distribution of the short period (2 ~ 8 s) agrees well with the surface tectonics. As the distribution between the Sichuan-Yunnan block, the Songpan-Ganzi block and the Sichuan Basin The boundary faults, the Longmenshan fault zone and the Xianshuihe fault zone have a clear control over the velocity structure of the upper crust in the above three blocks. The low-speed foreland character of the Sichuan Basin indicates that there is a thick (about 10 km) sedimentary cover in the corresponding area Layer; (2) medium cycle (12 ~ 18 s) phase velocity The degree distribution shows that the upper and upper crustal velocity structures of Sichuan-Yunnan block and Songpan-Garzê block have obvious non-uniform lateral variation, and the formation of block structures with different scales and high and low velocities, and the middle crust of Sichuan Basin has been (3) The distribution of long-period (25-35 s) phase velocities indicates that the middle and lower crusts of the Songpan-Ganzi block, especially the Sichuan-Yunnan block, show a wide range of obvious low-velocity anomalies, meaning that their middle and lower crust Relatively weak, while the middle and lower crusts of Sichuan Basin show a relatively high overall rate, which means that the Sichuan Basin has a relatively hard middle and lower crust. And taking the epicenter of the Wenchuan earthquake as a boundary, the crustal structure of the Longmenshan fault zone shows that the northern segment is High-speed anomalies, the southern section of low-speed anomalies of the segmentation features.