Present-day deformation and stress state of Longmenshan fault from GPS results-comparative research on active faults in Sichuan-Yunnan region

The 2D finite element model of Sichuan-Yunnan Region was established in this paper. The deformation movement of the main faults in this region is simulated by using the 'block loading' method and GPS data from 1999 to 2007. The simulated slip rate and stress accumulating rate along Longmenshan Fault is compared with those of other faults to determine the particular geodynamic condition which may have caused Wenchuan Earthquake and Lushan Earthquake. The results show that before Wenchuan Earthquake the right-lateral slip rate and the thrusting rate along Longmenshan Fault were respectively similar to 1 mm . a(-1) and similar to 0. 5 mm . a(-1), which were fairly lower than other faults while the stress was relatively high and of the same magnitude compared with other faults. In addition, the axis of principal compressive stress is perpendicular to the fault strike with a wide compressive zone. The accumulating rate of compressive pressure on the fault surface was -333. 74 Pa . a(-1), which was the highest among the faults in the region. The results above indicate that the compressive stress in the east of Bayan Har block and Longmanshan Fault had been increasing rapidly which lead to the local real stress being at high level and accordingly seismic activities. During this seismic active period, strong earthquakes should occur in clustering fashion. As a result; Wenchuan 8. 0 earthquake and Lushan 7. 0 earthquake successively occurred in less than 5 years.