The relationship between stress changes and strong earthquakes since 1900 around the Bayan Har block in northern Tibet, China

Abstract

Abstract A 3D viscoelastic finite-element model of the Qinghai-Tibet Plateau, including the Bayan Har block, is established in this article. This model takes into consideration differences in the regional geological structure, the main active fault zone, the active tectonic block (hereafter referred to as a block) and boundary fault zone, the irregular topography and layered lithospheric structure, and the seismic velocity structure of the crust and mantle. Moreover, the present tectonic background stress field in the research area is reconstructed using the constraints of the observed values for the rate of crustal horizontal movement and the direction of maximum principal compressive stress. On these bases, the historical strong earthquake sequences with Ms\u202f≥\u202f7 that have occurred around the Bayan Har block since 1900 AD are simulated. Based on the Coulomb failure stress and equivalent stress data, the relationships between stress evolution and strong earthquakes, the interactions between strong earthquakes are investigated. In addition, we have also explored the changes in stress on the Longmenshan fault zone before and after the 2008 Wenchuan earthquake, as well as the relationships between stress evolution and regional seismicity. The results show that the occurrence of strong earthquakes around the Bayan Har block may be related to the increase in the total stress in the source area. The influence of long-term tectonic stress loading on strong earthquakes cannot be ignored. The 2008 Wenchuan earthquake induced an increase in stress in the southern section of the Longmenshan fault zone, indicating that the 2008 Wenchuan earthquake has an obvious promoting effect on the 2013 Lushan earthquake. The seismicity of the Bayan Har block and its adjacent areas may be affected by the regional total stress state.