Using a topography-dependent tomographic scheme, the seismic velocity structure of the Eastern Tibetan Plateau, including the uplifted Longmenshan (LMS) orogenic belt, is accurately imaged in spite of the extreme topographic relief in the LMS region and thick sedimentary covers in the neighbouring Sichuan Basin. The obtained image shows a high-resolution upper crustal structure on a 500 km-long profile that is perpendicular to the LMS. The image clearly shows that the crystalline basement was uplifted within the LMS orogenic belt, and that the neighbouring Songpan-Ganzi Terrane was covered by a thick flysch belt, with evidence of near-surface thrust faults caused by convergence between Eastern Tibet and the Sichuan Basin. The indication that the lower crust beneath the LMS was folded and pushed upwards and the upper crust was removed by exhumation, supports the concept of a lower crustal channel flow beneath Eastern Tibet. The image also reveals that the destructive Wenchuan earthquake of year 2008 occurred in the upper crust, directly at the structural discontinuity between Eastern Tibet Plateau and the Sichuan Basin.

译文

采用地形相关的层析方案,尽管LMS地区地形起伏极端,邻近的四川盆地沉积覆盖层较厚,但仍准确成像了包括隆升龙门山 (LMS) 造山带在内的青藏高原东部地震速度结构。所获得的图像显示了垂直于LMS的500   km长轮廓上的高分辨率上地壳结构。图像清楚地表明,LMS造山带内的结晶基底隆起,邻近的松潘-甘孜地体被厚的飞石带覆盖,有西藏东部和四川盆地之间的会聚引起的近地表逆冲断层的证据。LMS下方的下地壳被折叠并向上推动,而上地壳被挖掘出的迹象支持了西藏东部下方的下地壳通道流的概念。该图像还揭示了2008年汶川破坏性地震发生在上地壳上,直接发生在青藏高原东部和四川盆地之间的结构不连续处。

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