Palaeoseismology and kinematics characteristics of the Xiaoyudong rupture, a short but significant strange segment characterized by the May 12, 2008, Mw 7.9 earthquake in Sichuan, China

Three faults were involved in the rupture process of the May 12, 2008 Mw7.9 Wenchuan earthquake, representing a rarely documented case of multiple faults rupturing simultaneously. Distinct from the other two major NE-trending surface ruptures, the ~ 7 km long Xiaoyudong surface rupture is oriented NW340° and shows thrust- and left- slip faulting. In order to understand what role Xiaoyudong rupture played in the tectonic evolution of Longmenshan thrust system, we conducted a detailed investigation including geomorphic feature observation, coseismic displacement measurement, paleo-rupture event trenching, and fault kinematic estimation of the Xiaoyudong area. Our results not only document an in situ paleoearthquake occurred at 3.2-2.3 ka BP, but also present the Xiaoyudong rupturing event as an oblique thrust with minor components of left lateral slip. We also found vertical and sinistral slip rate estimated as 1.1-1.5 mm/yr and 0.5-0.7 mm/yr, respectively. Finally, we suggest that the Xiaoyudong rupture is not a passive tear fault but an active participator of slip partitioning on multiple faults within the Longmenshan thrust system, and moreover, it gave strong response to both the 2008 and the penultimate earthquake while it kept silence with the antepenultimate event. ⺠This study documented an in situ paleoearthquake occurring at 3.2-2.3 ka BP near the town of Xiaoyudong; ⺠The Xiaoyudong rupturing event was presented as an oblique thrust with minor components of left- lateral slip; ⺠This study put a few essential constraints on the thrusting process of the Longmenshan tectonic system and suggest that the Xiaoyudong rupture is not a passive tear fault but an active participator of slip partitioning on multiple faults within this thrust system.