Analysis of the stress environment of the 2008 and 2014 Yutian Ms7.3 earthquakes

An M(s)7. 3 earthquake occurred on 21 March, 2008 in Yutian, Xinjiang Uygur Autonomous Region. Six years later, on 12 February 2014, another M(s)7. 3 earthquake happened about 100km apart from the former one in the same area. Focal mechanism shows that the earthquake in 2008 is associated with strike-slip fault, and the one in 2014 is related to normal fault. We calculate the velocity field, stress field and strain field of the research area using 3D Finite Element Method numerical simulation, and compare the simulating result with the actual observational data. The relative movement directions of several main strike slip faults derived from numerical simulation result are consistent with field geological observation, which shows the reliability of our simulation. Based on the numerical result, we further discuss the stress environment, seismogenic mechanics and dynamic factor of two earthquakes. It is suggested that Yutian and its neighborhood area are mainly in northeast-southwest compression and northwestsoutheast extension. Under the constraints of GPS velocity, the principal extensional strain rate in northwest-southeast direction is much greater than compression strain rate in 2008 Yutian earthquake epicenter, which led to normal fault in NNE direction. While the principal extensional strain rate is nearly equal to the principal compression strain rate in 2014 Yutian earthquake epicenter, which can easily cause sinistral strike slip fault in NEE direction.