Fault Geometries and Structures Associated With the Rupture Endpoints of the 2008Mw7.9 Wenchuan Earthquake, Eastern Tibet Plateau, China

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AbstractThe 2008 Wenchuan earthquake (Mw7.9) initiated at the southern part of the Yingxiu‐Beichuan fault of the Longmen Shan fault zone, eastern Tibet Plateau. The earthquake rupture propagated northeast for ~300 km, producing dextral‐thrust slip along the fault zone. Numerous studies have documented the characteristics of the rupture zone; however, the exact endpoints and the termination structures at both ends remain poorly constrained. On the northeasternmost rupture section, the aftershock distribution extends ~50 km along strike past the end of the observed surface rupture, suggesting that the rupture may extend northeastward at depth. Our field observations show that the aftershock zone follows a NE‐trending linear trace indicative of an active fault at the surface and confirm that the Qingchuan fault, which is one of the faults of the northeastern Longmen Shan fault zone and is reported to have ruptured during the 2008 earthquake by some studies, did not rupture during the Wenchuan earthquake. Detailed investigations show that the rupture terminated at an area between the Qingchuan and the Bahai‐Yuquanba faults where these two faults bound a 10‐ to 20‐km wide mountain block. To the southwest, the southwesternmost end of the Wenchuan earthquake rupture zone terminated south of Sanjiang, where a NE‐trending 50‐cm high fault scarp marks the endpoint of the surface rupture. Our study suggests that fault step overs at the northeastern and southwestern segments may have acted as a barrier to rupture propagation and thus play an important role in controlling the rupture propagation but were not critical in terminating the rupture, whereas the cross structures and/or stratigraphy (complex or massifs) in the northeastern and southwestern rupture endpoints area appear to have controlled the rupture termination.