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

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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.