Stress modulation of the seismic gap between the 2008 Ms 8.0 Wenchuan earthquake and the 2013 Ms 7.0 Lushan earthquake and implications for seismic hazard

Between 2008 and 2013, the M-s 8.0 Wenchuan earthquake and the M-s 7.0 Lushan earthquake occurred successively in the Longmenshan fault one. Their aftershocks delineated a prominent seismic gap approximately 50 km long, hereafter referred to as the WLSG. The possibility of an event of M-s 7.0 or above occurring in the WLSG is a matter of great concern. In this study, we estimated the change of Coulomb failure stress (Delta CFS) along the WLSG caused by historical earthquakes in the last 300 yr. Our results revealed that 20 major earthquakes cast a stress shadow on the WLSG before 2008 (-148.7 to -7.0 kPa), hindering the rupture of the Wenchuan earthquake and the Lushan earthquake. The Wenchuan earthquake had an important influence on the stress redistribution of the WLSG, resulting in significant stress increase (14.7 to 337.5 kPa). As of 2018, although the negative Delta CES caused by historical earthquakes (especially the Dayi earthquake) pushed the southern end of the WLSG away from failure, the positive peak Delta CFS of 323.0 kPa greatly encouraged the rupture of the northern WLSG. The small afterslip and weak microseismicity indicate that the WLSG is a stress barrier with high seismic potential, which can explain the mechanism of rupture termination of the Wenchuan earthquake and the Lushan earthquake.