Collaborative Proposal: Active Faulting Within the Eastern Tibetan Margin and western Sichuan Basin, P.R. China

西藏东缘是世界上最神秘的高原边缘之一。 海拔从四川盆地内的不到500米上升到6.5公里以上，距离约30至50公里。 这比喜马拉雅山脉的前缘更陡，喜马拉雅山脉的起源是西藏下面的印度次大陆的活跃逆冲。 然而，与喜马拉雅山形成鲜明对比的是，西藏东缘显示出微弱的活动逆冲证据。 此外，缺乏一个重要的沉积盆地毗邻的边缘和大地缩短的情况下，进一步证明了活跃的逆冲作用的insignificance。新的实地调查表明，虽然活跃的逆冲作用确实是稀缺的，有充分的证据，显着的活跃走滑断层。 初步勘察现场调查显示，有三个，可能是四个明显的右行走滑断层，走向东北，和两个主要的左行走滑断层，走向~N-S。 现在的研究重点是确定这些断层的速率和详细的几何形状，其中每一个断层都是限制该地区相对地壳运动的计划中的关键组成部分。 这些观测结果能够限制各种假设，从而使我们能够了解西藏边缘这一部分的演化。早期的调查还揭示了四川盆地内存在重要活动断层的可能性。 这一点特别令人关注，因为可疑断层可能代表着明显的强烈地面运动，而四川盆地是约6000万人的家园，断层滑动的速度正在通过仔细的采样策略来确定，通过宇宙成因放射性核素分析来估计被断层抵消的地貌的年龄。 活动断层的类型和模式是通过结合图像分析、地形分析和在野外勘测工作中确定的区域的详细野外测绘来确定的。 滑动速率和断层几何形状的组合产生一组运动学，区分竞争模型。

The eastern margin of Tibet is one of the most enigmatic plateau margins in the world. Elevations rise from less than 500 m within the Sichuan Basin to more than 6.5 km over a distance of about 30 to 50 km. This is steeper than the Himalayan front, which owes its origin to the active thrusting of the Indian subcontinent under Tibet. In stark contrast to the Himalaya, however, the eastern margin of Tibet shows insignificant evidence of active thrusting. Moreover, the lack of a significant sedimentary basin adjacent to the margin and the absence of geodetic shortening further testify to the insignificance of active thrusting.New field investigations indicate that while active thrusting is indeed scarce, there is ample evidence for significant active strike-slip faulting. Initial reconnaissance field investigation reveals three and possibly four significant right-lateral strike-slip faults that trend NE, and two major left-lateral strike-slip faults that trend ~N-S. Research is now focused on determining the rates and detailed geometry of these faults, each of which are critical components in planned attempts at constraining relative crustal motions in the region. These observations are able to constrain the various proposed hypotheses and therefore enable us to understand the evolution of this part of the Tibetan margin.Early investigation has also revealed the likelihood of significant active faulting within the Sichuan Basin. This is of particular concern, because the suspect faults may represent significant strong ground motions and the Sichuan Basin is home to about 60 million people.Rates of fault slip are being determined by a careful sampling strategy whereby the ages of landforms that have been offset by faulting are being estimated by cosmogenic radionuclide analyses. The style and pattern of active faulting is being determined by a combination of imagery analysis, topographic analyses, and detailed field mapping in regions previously identified during reconnaissance field work. The combination of slip rates and fault geometry yields a set of kinematics that discriminate among the competing models.