Study of Coseismic Damage and Post-mainshock Healing on the Longmen-Shan Fault Ruptured in the 2008 M8 Wenchuan Earthquake in China

该奖项由2009年美国复苏与再投资法案(公法第111-5条)资助。位于青藏高原东缘、中国西部的龙门山断裂具有活动构造的特点。在2008年5月12日汶川特大地震中，断裂带全长300公里，最大滑移量大于9米。其破裂长度、滑动和震级与1857年和1906年加州大地震的破裂长度、滑动和震级相当。PI和学生将利用汶川地震后四川地震台网(SSN)记录的数据和部署在破裂处的便携式地震仪，研究与这次8级地震相关的LSF上的同震岩石破坏和主震后恢复。我们将在1万多次汶川余震中识别重复地震群，并利用它们的波形数据来测量汶川地震引起的地震速度的时间变化。他们还将利用近断层台站记录的余震产生的断层带捕获波来描绘LSF上低速损伤区的地下结构。龙门-山断裂的结果将与我们之前对1992年7.4级陆地地震和1999年赫克托矿震的Parkfield San Andreas断层和破裂带岩石损伤和修复过程的研究结果进行比较。由于四川地震台网记录的2008年汶川8级地震前震和余震序列的数据密度很高，这项研究将是少数几个与8级大地震有关的发震深度断层带岩石损伤和修复的研究案例之一。丰富的汶川8级地震的意外资料将提高我们研究活动断裂性质和破坏带深度的时空变化的分辨率。断裂带破坏的空间范围以及地震周期中强度的损失和恢复是理解断层力学和物理学的关键因素。通过中国大地震与美国大地震的对比，最基本的断裂带状态信息有助于全球对地震过程和灾害的了解。这项工作将使我们能够确定大地震时断裂带的物理性质的演化，记录破坏性地震的特征，并帮助我们评估美国和中国发震区的潜在地震危险性。本次汶川8级地震研究项目将根据《中美地震研究议定书》开展。该项目将涉及博士后和研究生研究员。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5) The Longmen-Shan Fault (LSF) located at the east margin of the Tibetan Plateau in western China is featured by active tectonics. It was broken in total length of 300 km with the maximum slip larger than 9 m in the devastating M8 Wenchuan earthquake on May 12, 2008. Its rupture length, slip and magnitude are comparable with those of the 1857 and 1906 big earthquakes in California. The PI and student will study the co-seismic rock damage and post-mainshock healing on the LSF associated with this M8 earthquake using the data recorded at the Sichuan Seismic Network (SSN) stations and portable seismographs deployed at the ruptures after the Wenchuan earthquake. We shall identify clusters of repeated earthquakes among more than ten thousands of Wenchuan aftershocks and use the waveform data from them to measure temporal changes in seismic velocity caused by the Wenchuan earthquake. They will also delineate the subsurface structure of the low-velocity damage zone on the LSF using fault-zone trapped waves generated by aftershocks recorded at near-fault stations. The results from the Longmen-Shan Fault will be compare to those obtained from our previous studies for the process of rock damage and heal at the Parkfield San Andreas Fault and rupture zones of the 1992 M7.4 Lands and 1999 M7.2 Hector Mine earthquakes.Because of the density of the data recorded at the Sichuan Seismic Network for the pre-shock and aftershock sequence of the 2008 M8 Wenchuan earthquake, this study will be one of a few cases to illuminate the in-situ fault-zone rock damage and healing at seismogenic depths associated with a big M8 earthquake. The wealth of unexpected data from the M8 Wenchuan earthquake will improve the resolution in our study of the spatio-temporal variations in properties of the active faults and the depth extent of the damage zone. The spatial extent of fault-zone damage and the loss and recouping of strength across the earthquake cycle are critical ingredients in understanding of fault mechanics and physics. With a comparison of big earthquakes in China with those in US, the most basic information on the in-situ state of the fault zone aids the understanding of earthquake processes and hazards globally. The proposed work will allow us to determine the evolution of fault-zone physical properties with a big earthquake, document characteristics of damaging earthquakes and help us to evaluate potential earthquake risk in seismogenic regions in USA and China. This research project on the M8 Wenchuan earthquake will be carried out under the Sino-US Earthquake Study Protocol. The project will involve post-doctoral and graduate researcher.