How Did the 2013 Lushan Earthquake (Ms = 7.0) Trigger its Aftershocks? Insights from Static Coulomb Stress Change Calculations

Abstract

The Lushan earthquake Ms7.0 occurred at 08:02 Beijing Time (00:02 UTC) on 20 April 2013, located on the eastern margin of the Tibetan Plateau, where the 2008 Ms8.0 Wenchuan earthquake took place. The other strong shock following the Wenchuan earthquake occurred on the Longmen Shan thrust fault. A large number of aftershocks were recorded after the mainshock. To investigate how the aftershocks were triggered, we firstly relocated the 6-month aftershock sequence by the double-difference algorithm. Next, we calculated Coulomb failure stress changes imparted by the Lushan mainshock both on the optimally oriented plane and on the aftershock nodal planes. Then we examined the correspondence between the Coulomb failure stress changes and the spatial distribution of the aftershocks. The computed results show that most of the aftershock hypocenters did not occur on the region with the positive Coulomb stress changes caused by the Lushan mainshock. Moreover, the majority of aftershock nodal planes were brought away from failure by coseismic Coulomb stresses. This implies that coseismic static Coulomb stress changes may not be the governing process for aftershock genesis. In contrast, postseismic stress transfer by processes of afterslip and pore fluid flow are assumed to play an important part in aftershock triggering, based upon the spatiotemporal distribution of the aftershocks.