The MS 8.0 Wenchuan earthquake ranks as one of the world's largest intraplate megathrust events in the last 150 years. Field investigation shows clear surface breaks along two thrusts, Beichuan and An XianGuan Xian (Pengguan) faults, of the NEtrending Longmen Shan thrust fault system. The principal rupture, on the NWdipping high angle Beichuan fault is over 200 km, possibly 225 km long. Slip on this fault is dominantly NW hangingwall up thrust in the south; to the northeast, it changes to oblique thrust with near equal amounts of thrust and rightlateral components. Maximum scarp height reaches ~11 m locally. Basinward of this rupture, another continuous surface break is observed for over 70 km on the parallel, shallowerNWdipping Pengguan fault. Slip on this latter fault was pure thrusting, with a maximum scarp height of 3~3.5 m. Wenchuan rupture is one of the very few reported instance of coseismic surface rupture on parallel thrusts. Because the coseismic rupture is partitioned on the highangle thrusts within the imbricate thrust system, rather than the frontal thrusts, Wenchuan rupture is thus an outofsequence thrusting event, similar to the 1999 Chichi M 7.5 and the 2005 Kashmir M 7.6 earthquakes, suggesting that outofsequence thrusting events are more common than previously thought. This long rupture, largeoffset, thrusting event calls for a reevaluation of the lower crustal channel flow models, which anticipate little or no active shortening of the upper crust along that edge of the plateau, and for an urgent quantitative reassessment of slip rates and paleoseismic behavior on other slowmoving yet with potential of large earthquakes, active faults along the denselypopulated eastern margin of the Tibetan plateau.