Kinematic and dynamic rupture characterization of the 2008 Ms 8 Wenchuan earthquake sequence

该奖项是根据《2009年美国复苏和再投资法案》(公法第111-5号)获得资助的。2008年5月12日，中国汶川7.9级地震是现代地球物理观测记录到的最大板内地震。它在以东北方向为主的龙门山下方约250公里处单边破裂，龙门山是一座陡峭的高山，西北与青藏高原接壤，东南与四川盆地接壤。强烈的地面震动导致500多万座建筑物倒塌，近7万人死亡。这次大地震的发生让地球科学界大多数人感到惊讶，因为震源区历史上缺乏大地震，而且根据地质和大地测量数据，滑移率非常低。这次灾难性地震及其余震序列将通过地震、大地测量和地质观测进行研究。破裂过程将受到约束，以与构造背景和地表观测相匹配，同时与包括本构摩擦定律在内的破裂动力学一致。对这种巨大的板内地震及其余震的定量了解有助于进行危害分析，这最终将有助于指导社会对未来事件的反应。美国有许多应变率非常低的地区，例如新马德里、查尔斯顿，那里发生了大震级地震。这项研究为理解低应变率地区板内地震的特征和过程提供了一个极好的机会。这是一个异常复杂的地震序列，涉及陡峭地形下的多个断层，但异常少有大余震。方法是使用最新的非线性方法来反演地震和大地测量数据，以确定运动学模型。分析的关键将是全力评估运动学模型中的不确定性，以及它们与地球结构、数据分布和被反演数据类型中的不确定性的关系。该运动学模型将作为3D全动态建模的基准，该3D动态建模将涉及多个断层面、地形和3D结构。本次地震的破裂特征是否不同于1999年集集地震等研究较多的逆冲地震，是否反映了其异常的构造加载过程？Ii)逆冲断裂是如何开始的？成核对随后的破裂有什么影响？Iii)两条断层上的破裂是如何动态相互作用的？4)这次地震激发的地面运动有什么特点？与其他大型推覆事件相比，地面运动是否不寻常？

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)The 12 May 2008 Mw 7.9 Wenchuan, China earthquake is the largest intraplate earthquake recorded by modern geophysical observations. It ruptured unilaterally about 250 km beneath the predominantly northeast-trending Longmen Shan, a steep high mountain range that bounds the Tibetan Plateau to the northwest and the Sichuan Basin to the southeast. The strong ground shaking caused over 5 million buildings to collapse and nearly 70,000 fatalities. The occurrence of this major earthquake surprised most of the geoscience community because the source region historically lacks large earthquakes and has a very low slip rate based on geological and geodetic data. This catastrophic earthquake and its aftershock sequence will be investigated with seismic, geodetic and geological observations. The rupture process will be constrained to match the tectonic background and surface observations, and at the same time be consistent with rupture dynamics that includes a constitutive friction law. Quantitative understanding of such giant intraplate earthquakes and their aftershocks can contribute to hazard analysis that will ultimately be useful for guiding societal response for the future events. There are many areas in United States with very low strain rates, e.g., New Madrid, Charleston, where large magnitude events have occurred. This research provides an excellent opportunity to take a large step forward in understanding the character and processes of intraplate earthquakes in areas of low strain rates. This is an unusual complex earthquake sequence involving multiple faults beneath steep topography, but with abnormally few large aftershocks. The approach is to use the newest nonlinear methods for inverting the seismic and geodetic data to determine a kinematic model. Critical to the analysis will be an all out effort to assess the uncertainties in the kinematic model and their relation to uncertainties in earth structure, data distribution and the type of data being inverted. This kinematic model will serve as the baseline for full dynamic modeling in 3D that will involve multiple fault planes, topography and 3D structure. This research addresses the following questions: i) Are the rupture characteristics of this event different from other well studied thrust earthquakes, such as 1999 Chi-Chi earthquake, perhaps reflecting its abnormal tectonic loading process? ii) How did the thrust rupture initiate? What effect did the nucleation have on the subsequent rupture? iii) How did the ruptures on two faults dynamically interact? iv) What are the characteristics of the ground motion excited by this earthquake? Are the ground motions unusual compared with other large thrust events?