Role of initial stress rotations in rupture dynamics and ground motion: A case study with implications for the Wenchuan earthquake
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abstract
Motivated by observations in the 2008 Mw 7.9 Wenchuan earthquake, we study effects of systematic changes in the principal stress orientation along the fault strike on rupture dynamics and ground motion using a 3D finiteelement method. Based on Anderson's theory of faulting, we set up the initial stress field with rotations in stress orientations along strike for a dynamic rupture model of a shallow dipping fault. We find that initial stress rotations along strike can cause dramatic changes in rupture speed and produce distinct patterns in slip distribution and peak ground motion. When a mismatch (unfavorable for faulting) between fault geometry and initial stress orientations is encountered, rupture can spontaneously stop. Some firstorder features in the Wenchuan event may be partially caused by rotations in the principal stress orientation along strike, such as the rupture arrest at the northeast end and two severe destruction zones in the observed seismic intensity distribution. These results may have important implications for assessing seismic hazards imposed by faults with changes in the initial stress field along strike worldwide.
