The stress evolution before the 2013 M7.0 Lushan earthquake in the Longmen Shan area since 1900

摘要

Strong earthquakes can disturb the regional stress field. The variation in the static Coulomb stress changes induced by earthquakes can explain the spatial distribution of certain aftershocks, and cascade earthquake sequences. However, the coseismic Coulomb stress change is not the only stress perturbation, interseismic and postseismic viscoelastic relaxation can also affect the evolution of the stress field. This study focuses on how stress perturbation from four strong earthquakes (the 1933 M7.5 Diexi, 1955 M7.5 Kangding, 1976 M7.2 Songpan and 2008 M8.0 Wenchuan) occurred around the Longmen Shan area in western China affect the occurrence of the 2013 Lushan M7.0 earthquake. In addition, we examine the stress evolution along the Longmen Shan fault zone and its adjacent faults to assess the regional seismic hazard. We construct a 3D viscoelastic finite element model that includes the fault structure, inhomogeneous medium, tectonic stress, gravity to simulate the evolutionary stress field when using observed Global Positioning System (GPS) vectors as the boundary conditions. The simulated results show that the coseismic Coulomb stress change induced by the Kangding, Songpan, and Wenchuan earthquakes is positive at the hypocenter of Lushan earthquake. In particular, the coseismic Coulomb stress change imparted by the Wenchuan earthquake exceeds the earthquake-triggering threshold of 0.01MPa, Additionally, the tectonic stress at the hypocenter of the Lushan earthquake increases with time, indicating the stress cumulates gradually at this location. We also compare the distribution of the earthquakes (from 1933 to 2013) with the effective and Coulomb evolutionary stress fields. Almost 70% of the earthquakes in the research region are located in the effective and Coulomb stress-enhanced areas. Our study helps to better understand the origin of Lushan earthquake and provide a theroetical basis for assesing regional seismic hazard.