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

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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?