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青藏高原东缘地区地形陡峭、起伏大,经历了新生代的快速冷却和剥蚀,却没有显示出该前陆盆地产生过大量级地壳缩短或调解过程的证据。我们通过应用各种地貌观测结果对平行于该高原边缘的几条大断层的运动和滑动速率进行约束,来论述这一矛盾。北川和彭灌断层主要是右旋滑动的活动构造,沿该高原边缘可连续追踪达200km。这两条断层都断错了河流填充阶地,得到的宇宙成因核素10Be经继承校正后,暴露物的年龄少于15ka,说明了晚更新世的活动。彭灌断层沿走向的两个地点在全新世看来活动过。两条断层晚第四纪的视下落速率沿走向是变化的,但一般都小于1mm/a。走滑位移的速率很可能要高出几倍,可能约为1～10mm/a,但仍旧约束不好。四川盆地西缘特别是山前带,在晚第四纪也发生了褶皱和右旋走滑活动。这些观测证明了该高原东缘形成和保持的模式,没有发生大的上地壳缩短。这些也表明,与青藏高原东缘平行的断层的活动可能预示着人口密集的四川盆地存在很大的地震危险性。
The eastern margin of the Qinghai-Tibet Plateau is characterized by steep, undulating terrain, rapid cooling and erosion during the Cenozoic, but no evidence of massive crustal shortening or mediation in the foreland basin. We discuss this contradiction by applying various geomorphological observations to constrain the motion and slip rates of several large faults parallel to the edge of the plateau. The Beichuan and Peng-Guan faults are mainly dextral slip tectonics and can be traced continuously up to 200km along the edge of the plateau. Both of these faults disrupted the river-filling terrace, and the derived cosmic radionuclide 10Be, with its inheritance corrected, exposed less than 15 ka, indicating Late Pleistocene activity. Two locations along the Peng-Guan fault appear to have been active during the Holocene. The Late Quaternary apparent velocities of the two faults vary along the strike, but are generally less than 1 mm / a. The rate at which slip is likely to be several times higher may be about 1 to 10 mm / a, but the constraints remain poor. The western margin of the Sichuan Basin, especially the piedmont belt, also experienced folds and dextral slip events in the late Quaternary. These observations demonstrate the pattern of formation and maintenance at the eastern margin of the plateau, with no major upper crust shortening. All these also indicate that the activity of the fault parallel to the eastern edge of the Qinghai-Tibet Plateau may indicate that there is a great earthquake risk in the densely populated Sichuan Basin.