Dynamic Rupture Simulations of the 2008 Mw7.9 Wenchuan Earthquake: Implication for Heterogeneous Initial Stress and Complex Multifault Geometry.

The 2008 Mw7.9 Wenchuan earthquake ruptured northwest‐dipping imbricate oblique reverse faults along the Longmenshan thrust belt at the eastern margin of the Tibetan Plateau, and developed one of the most complex coseismic rupture patterns for reverse faulting events ever reported in intraplate settings. To evaluate to what extent complex fault geometry and heterogeneities in initial stress can explain the characteristics of coseismic observations, we simulate spontaneous dynamic rupture propagation governed by slip‐weakening friction law on the geometrically complex multifault system loaded by heterogeneous stress. Our model reproduces many observed features including the multifault ruptures, locations of the maximum slip, Interferometric Synthetic Aperture Radar observations, source time functions and peak ground velocities. Our results suggest that the maximum horizontal principal stress in the northern part of Beichuan Fault (BFC) is rotated approximately 6.5° counterclockwise compared to that in the southern part of BFC, yet this rotation is not sufficient to produce a supershear rupture. We infer that the fault core zone in the southwestern Beichuan Fault (BCF) may have been more severely damaged than the northeastern counterpart, which provides an explanation that the rupture in the northern BCF propagates faster than in the southern portion. Besides, we find that Coulomb failure stress changes on Wenchuan‐Maoxian Fault (WMF) may be counteracted by the aftershock slips of the Lixian Fault, which suggests Wenchuan earthquake could not significantly push the WMF closer to failure. Plain Language Summary: The 2008 Wenchuan earthquake caused great destruction to cities and counties along the northwestern margin of the Sichuan Basin. At least three faults slipped in this event, showing complex surface deformation. In this study, we develop a complex non‐planar multifault model containing heterogeneities tectonic stress, using computer simulation to reproduce dynamic rupture process of this event. The results derived from simulations are well consistent with many observed features, and help to explain why the zones near Yingxiu and Beichuan towns suffered the most intensive shock. Also, our numerical simulations help to constrain the distribution of spatial tectonic stress fields. Furthermore, we infer that the fault core zone in the southwestern Beichuan Fault may have been more severely damaged than the northeastern counterpart, which provides an explanation that the rupture in the northern Beichuan Fault propagates faster than in the southern portion. Besides, we found that the mainshock has increased the Coulomb failure stress on the Wenchuan‐Maoxian Fault (WMF), which did not slip in this event. However, we speculate the mainshock could not significantly push the WMF closer to the edge of a new earthquake. Key Points: Our model with complex multifault geometry and heterogeneous initial stress reproduces major observations of the Wenchuan earthquakeThe rupture speed variations may be caused by the fault damage zones difference, rather than fault geometry and stress heterogeneityThe positive Coulomb stress changes on the Wenchuan‐Maoxian Fault caused by the mainshock may be relaxed by aftershocks on Lixian fault [ABSTRACT FROM AUTHOR]