Surface rupture in the 12 May 2008 Sichuan earthquake

2008年5月12日在四川省发生的中国地震，震级为7.9级，摧毁了中国西部的大片地区。地震发生在世界上一些最陡峭、最崎岖的山脉--龙门山之下。这一山脉比喜马拉雅山脉更陡峭，形成了青藏高原的东部边缘，青藏高原是印度和欧亚大陆之间5公里高的碰撞带。龙门山的起源有些神秘，因为该地区相对较少显示出构造活动的迹象，也很少发生历史地震。尽管这种平静，但PI和Co-I之前的工作表明，龙门山的断层在地质上最近是活跃的，在过去的10000年里发生了地震。两条长断层，特别是北川和彭关断层，几乎贯穿了龙门山的整个长度，显示出过去几千年、有时甚至数百年来发生过地震的明显证据。滑移率从每年几分之一毫米到可能每年许多毫米不等。然而，该地区陡峭的地形和高降雨量意味着，过去这些地震的证据很快就会因侵蚀而消失，因此这些对滑移率的估计，甚至是断层的确切位置，都非常不确定。5月12日的地震提供了一个前所未有的机会来观察下伏断层上的几何形状和滑动感，并了解造成龙门山的短期和长期变形模式之间的关系。在拟议的研究中，我们将绘制地震中发生的地表滑动的模式，并测量沿破裂带不同点处的滑动方向和滑动量。这次地震似乎发生在北川断裂上，但地表滑动方式复杂，可能涉及多条断层。解开这种复杂性的细节是理解地表以下断层之间的几何关系，以及这些断层随着时间的推移相互作用和演化的好方法。地震中滑移的分布可以直接与基础设施的破坏模式和地震引发的山体滑坡的发生进行比较。它还可以用来检查和校准估计地震规模的快速、远程方法，如地震学或基于卫星的遥感技术。

The 12 May 2008 earthquake in Sichuan Province, China, had a magnitude of 7.9 and devastated a large area of western China. The earthquake occurred beneath some of the steepest and most rugged mountains in the world, the Longmen Shan or Dragon's Gate Mountains. This range, steeper than the Himalaya, forms the eastern edge of the Tibetan Plateau, the 5 km high collision zone between India and Eurasia. The origin of the Longmen Shan are somewhat mysterious, because the region shows relatively little sign of tectonic activity and has had very few historical earthquakes. Despite this quiescence, previous work by the PI and Co-I has shown that the faults in the Longmen Shan have been active in the geologically-recent past, with earthquakes in the last 10000 years. Two long faults in particular, the Beichuan and Pengguan faults, run almost the entire length of the Longmen Shan and show clear evidence of earthquakes during the last few thousands, and in some cases hundreds, of years. The rates of slip vary between fractions of mm per year to possibly many mm per year. The steep topography and high rainfall in the region, however, mean that the evidence of these past earthquakes is quickly lost through erosion, and so these estimates of slip rates and even the exact locations of the faults are very uncertain. The 12 May earthquake provides an unprecedented opportunity to view the geometry and sense of slip on the underlying faults, and to see the relationships between the short-term and long-term patterns of deformation that have created the Longmen Shan. In the proposed research, we will map the pattern of surface slip that occurred in the earthquake and measure the orientation and amount of slip at different points along the rupture zone. The earthquake appears to have occurred on the Beichuan fault, but the pattern of slip at the surface is complicated and it may be that more than one fault was involved in the earthquake. Untangling the details of such complexity is a good way of understanding the geometrical relationships between faults below the surface, and the way in which the faults have interacted and evolved over time. The distribution of slip in the earthquake can be directly compared to the pattern of damage to infrastructure and the occurrence of earthquake-triggered landslides. It can also be used to check and calibrate rapid, remote methods of estimating earthquake size, such as seismological or satellite-based remote sensing techniques.