The static Coulomb stress change of the 2013 Lushan M_S7.0 earthquake and its impact on the spatial distribution of aftershocks

On 20 April 2013, a M_S7.0 earthquake struck Lushan County, Sichuan Province. The epicenter is on the southwest segment of the Longmenshan fault zone which is only about 85 km from the 2008 Wenchuan M_S8.0 earthquake only after 5 years. This paper first calculated the impact of Coulomb stress change induced by the Wenchuan earthquake on the Lushan earthquake, and found that the Lushan earthquake have been triggered by the Wenchuan earthquake (Coulomb stress increased by 0.012 MPa). Then the Coulomb stress change generated by the Lushan earthquake and the Wenchuan earthquake were calculated. The results show that the aftershocks have been promoted by the combined effect of the two strong earthquakes. More than 85% of the aftershocks occurred in the Coulomb stress increasing region. However, the Lushan earthquake alone cannot trigger the aftershock sequence (only 48.7% aftershocks fall into the increasing region). Furthermore, the calculation result also indicate that the Lushan earthquake has little influence on the surrounding faults. Only the northeast segment of the Longmenshan fault is brought closer to failure. Due to the Wenchuan earthquake, most of the surrounding faults, such as the Anninghe, Daliangshan, Barkam, Minjiang and Huya faults are being unloaded, while the southeast segment of the Xianshuihe fault and middle segment of the Longmenshan fault are enhanced, accelerating occurrence of new earthquakes.