Geometric Control on Seismic Rupture and Earthquake Sequence Along the Yingxiu‐Beichuan Fault With Implications for the 2008 Wenchuan Earthquake

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AbstractThe 2008 Mw 7.9 Wenchuan earthquake is the most disastrous seismic event in China since 1976. Both field and seismological investigations suggest a multi‐stage coseismic rupture with most damage associated with the Yingxiu‐Beichuan Fault (YBF) of spatially variable fault strike and dip angles. To investigate the effect of fault geometric complexity on coseismic rupture and paleoseismic pattern on the YBF, we perform earthquake sequence modeling on 3D fault geometry in the framework of rate‐and‐state friction law. Our model produces a long‐term earthquake sequence with quasi‐regular recurrences of whole‐fault ruptures and segmented ruptures. The along‐strike rupture segmentation, earthquake propagation speed, and slip rate are mainly controlled by along‐strike variations of fault dip and strike angles. Particularly, the YBF can be divided into two segments: the southern segment featured by large events (Mw > 8.0) and the northern segment with smaller events (Mw < 7.5), with recurrence intervals primarily determined by the tectonic loading rate. In a whole‐rupture event, the rupture speed mainly correlates with the fault dip angle; a smaller dip angle results in a wider seismogenic zone and higher rupture speeds, whereas the small‐scale variation in rupture speed is regulated by the fault strike angle. The effect of strike variation on the total coseismic slip amount is more pronounced due to the large strike angle gradient along the YBF. After varying the slip vector to reflect the northward transition from the dominant thrust‐slip to strike‐slip faulting during the Wenchuan coseismic rupture, we obtain reasonably good agreement of model simulated coseismic surface displacements with GPS observations.