Coulomb Stress Change and Evolution Induced by the 2008 Wenchuan Earthquake and its Delayed Triggering of the 2013 Mw 6.6 Lushan Earthquake

Abstract

Online Material: Table of GPS velocities. Almost five years after the 12 May 2008 M w 7.9 Wenchuan earthquake, the Longmenshan fault zone was struck by the April 20 M w 6.6 Lushan earthquake, with its hypocenter located ∼45 km southwest of the southern end of the Wenchuan surface rupture (Han et al. , 2014; Zhang et al. , 2014; Fig. 1). Such proximity in space and time between the two events implies that the later event is an aftershock of the previous one, or in other words, the previous event played a more important role in the occurrence of the latter than the long‐term tectonic loading did. Early studies on the problem had split opinions. On one hand, Du et al. (2013), Liu et al. (2013), and Xu et al. (2013) considered the two earthquakes as independent events. Wang et al. (2013) and Parsons and Segou (2014), on the other hand, claimed that the Lushan earthquake should be viewed as an aftershock of the Wenchuan earthquake. Whereas each group has its own basis of reasoning, lack of quantitative examination makes these claims less convincing. In recent years, Coulomb stress change has been widely used in estimating magnitude of stress loading for identification of areas or structures at increased risk of earthquake triggering (e.g., Harris, 1998; Stein, 1999; Chery et al. , 2001; Freed and Lin, 2001; Pollitz and Sacks, 2002; Freed, 2005; Steacy et al. , 2005; Gomberg and Felzer, 2008). In this paper, we apply this method to investigate to what extent the Lushan earthquake has been triggered by the Wenchuan earthquake. Previous studies have explored the consequence of the 2008 Wenchuan earthquake on the changes in Coulomb stresses on …