Strong earthquake clustering around the eastern Tibetan Plateau after the 2008 MW7.9 Wenchuan earthquake

After the 2008 M(W)7.9 Wenchuan earthquake, the eastern Tibetan Plateau experienced a series of M-W>6.0 earthquakes, including the 2013 M(W)6.6 Lushan, 2014 M(W)6.1 Kangding and 2017 M(W)6.5 Jiuzhaigou events. Based on available constraints, we build a three-dimensional viscoelastic finite element model to calculate Coulomb failure stress caused by these strong earthquakes. In this model, the geometry and slip vector of the initial rupture zone of each earthquake are used to better evaluate the earthquake-related stress projection. Considering reasonable ranges of viscosities for the crust and upper mantle in different tectonic units, numerical results show that after the Wenchuan earthquake, the coseismic Coulomb failure stress change at the hypocenters of the subsequent earthquakes increased to approximately +0.012-+0.040, +0.01-+0.03, and +0.008-+0.015 MPa, respectively. With viscoelastic relaxation of the lower crust and upper mantle, the Coulomb failure stress change at the hypocenters of these earthquakes accumulated to about +0.014-+0.042, +0.016-+0.036, and +0.003-+0.007 MPa just before their occurrence. This suggests that the Wenchuan earthquake indeed triggered or hastened the occurrence of the Lushan, Kangding and Jiuzhaigou events, supporting that strong earthquake clustering around the eastern Tibetan Plateau could be related to stress interaction between the seismogenic faults. Besides, -94% and -6% of the stress increase around (and before the occurrence of) the Kangding earthquake were contributed by the Wenchuan event and the Lushan event, respectively; the positive Coulomb failure stress change at the Jiuzhaigou earthquake hypocenter was related to coseismic slip partitioning of the Wenchuan earthquake. This means that stress interaction among the earthquakes could be controlled by the combined effect of stress of the previous events and by the complexity of earthquake ruptures. Thus, in researches on the earthquake-triggering mechanism, special attentions should be paid on both details of the rupture model and multiple factors of previous earthquakes.