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Analysis of the Crust Deformations before and after the 2008 Wenchuan Ms8.0 Earthquake Based on GPS Measurements

DOI: 10.1155/2011/802346

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Abstract:

We use the movement velocities of GPS stations in western Sichuan province, China, to determine the distribution of horizontal strain accumulation before the 2008 Wenchuan Ms8.0 earthquake with a piecewise approximation approach and the coseismic displacements to determine the fault slips of the earthquake with an inversion analysis method. The results show that the distribution of the principal strain rates is strongly related to the active faults in the region, but along Longmenshan fault where the earthquake occurred, the strain rates are much lower than the others. The fault slip distribution shows mainly a thrusting with dextral striking, and the fault slips in the upper parts of the fault plane are in general bigger. Using the current strain accumulation rate and the released energy by the earthquake, we predict such a big earthquake in Longmenshan fault zone will happen in 460 to 1380 years. 1. Introduction On May 12, 2008, a disastrous earthquake of magnitude Ms8.0 occurred in Wenchuan, Sichuan province, China, killing more than 69,000 people and injuring over 370,000 people [1]. Figure 1 shows geological setting in this area. The earthquake occurred at the east boundary of Tibet plateau and the west front of Sichuan basin and is believed to be caused by the collision between Indian plate and Eurasian plate. The red lines show the traces of active faults [2]. The Ms8.0 Wenchuan earthquake occurred in the Longmenshan fault zone (LMSFZ). The LMSFZ mainly consists of three parallel faults running from northeast to southwest [1]: Wenchuan-Maoxian fault (WMF), Yingxiu-Baichuan-Qingchuan fault (YBQF), and Guanxian-Anxian fault (GAF). The Wenchuan Ms8.0 earthquake occurred along over 300?km long YBQF and 40?km long GAF simultaneously [3]. There are 10 aftershocks with magnitude greater than 5.5 within three months near the main earthquake fault YBQF [1]. Figure 1: Geological setting. WMF is Wencuan-Maoxian fault, YBQF is Yingxiu-Baichuan-Qingchuan fault, GAF is Guanxian- Anxian fault, XSHF is Xianshuihe fault, ANHF is Anninghe fault, and LQSF is Longmenshan fault. The red circles represent the main- and aftershocks with magnitude greater than 6.0. The red lines show the active faults based on [ 2]. The inset map shows relative plate motion and the location of our study area. The black arrows show direction and magnitude of plate movements relative to the fixed Eurasian plate, and the black box shows the location of our study area, the western Sichuan province, China. After the earthquake, the area attracted a lot of attentions in scientific community.

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