Phase velocity array tomography of Rayleigh waves in western Sichuan from ambient seismic noise
Phase velocity array tomography of Rayleigh waves in western Sichuan from ambient seismic noise
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发表时间：
2010
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通讯作者：
Li Yu;Cheng Jiu;L. Shun
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作者：
Li Yu;Cheng Jiu;L. Shun
中国地震局地质研究所地震动力学国家重点实验室于2006年在川西地区(26°N~32°N，100°E~105°E)布设了297个宽带台站的可移动台阵。利用互相关技术获得了面波经验格林函数，并测量了所有可能的台站对的瑞雷波相速度频散曲线，然后利用这些频散测量结果反演了周期2~35之间的瑞雷波相速度图。结果表明，川甸地块、松潘-甘肃地块与四川盆地的地壳结构存在显著差异，主要表现在：(1)短周期(S 2~8)相速度图与地表地质特征有很好的相关性，川甸地块的上地壳结构，以及川甸地块的上地壳结构，松潘-甘泽地块和四川盆地受龙门山断裂和鲜水河断裂的良好制约，尤其是四川盆地的前陆，其显著的低速构造表明确实存在厚重的沉积；(2)中期(S 12~18时)相速度图显示，川甸地块和松潘-甘孜地块的中下地壳速度结构具有明显的横向非均质性，包括大小不一的低速带，而四川盆地下的上、中地壳则表现为高速度结构；(3)长周期(S 25~35)相速度图显示，松潘-甘孜地块和川甸地块在中下地壳具有明显的低速异常，表明这两个地块的中下地壳相对较弱，四川盆地中下地壳具有较强的中下地壳力学异常，尤其是龙门山断裂沿线的地壳速度结构北有高速异常，南有汶川地震震中以南的低速异常。
A transportable array with 297 broadband seismic stations was deployed in the western Sichuan (26°N～32°N, 100°E～105°E) in 2006 by the State Key Laboratory of Earthquake Dynamics,Institute of Geology, China Earthquake Administration.From the ambient noise data recorded at 156 stations of this array to the north of 29°N from January to December of 2007, we have obtained the surface wave empirical Green's functions (EGF) using cross-correlation technique and measured the Rayleigh-wave phase velocity dispersion curves for all possible station pairs.These dispersion measurements were then used to invert for phase velocity maps of Rayleigh waves between periods 2～35 s.Our results manifest the significant discrepancies between the crustal structures of the Chuandian block, Songpan-Garze block and Sichuan basin, which can be summarized as follows.(1) The phase velocity maps at the short periods (2～8 s) are well-correlated with the surface geological feature, and the upper crust structures of the Chuandian block,Songpan-Garze block and Sichuan basin are well confined by the Longmen Shan faults and Xianshuihe faults, especially in the foreland of the Sichuan basin, where the significant low-velocity structure suggests that a thick sediment does exist;(2) The phase velocity maps at the intermediate periods (12～18 s) manifest that the middle and lower crust velocity structure of the Chuandian and Songpan-Garze block has apparent lateral heterogeneities, including low- velocity zones of different sizes, and the upper and middle crust beneath the Sichuan basin shows high velocity structure;(3) The phase velocity maps at the long periods (25～35 s) manifest that the Songpan-Garze block and Chuandian block have an evident low-velocity anomaly in the middle-lower crust, suggesting that the middle-lower crust of these two blocks is relatively weak, and the middle-lower crust of Sichuan basin has high-velocity anomaly, suggesting a mechanically strong middle-lower crust in the basin.In particular, the crustal velocity structure along the Longmen Shan faults has a high-velocity anomaly to the north and a low-velocity anomaly to the south of the hypocenter of the Wenchuan earthquake.