Structural analysis of the right-lateral strike-slip Qingchuan fault, northeastern segment of the Longmen Shan thrust belt, central China

摘要

The eastern margin of the Tibetan Plateau is marked by the Longmen Shan thrust belt (LSTB), which is dominated by thrust faults and thrust-related fold structures that is home to the 2008 M_W 7.9 thrusting-type Wenchuan earthquake. Although previous works demonstrated that the seismogenic fault for the earthquake changed coseismic slip sense from thrust-dominated slip in the central and southeastern segments of the LSTB to right-lateral strike-slip-dominated displacement along the Qingchuan fault (northeastern segment of the LSTB), the related structures and current activity of the Qingchuan fault remains unclear. Topographic analyses of 0.5-m-resolution WorldView imagery and Digital Elevation Model (DEM) data, field investigations and structural analysis of the fault zone reveal that: ⅰ) stream channels and late Pleistocene-Holocene terrace risers and alluvial fans are systematically offset dextrally along the Qingchuan fau ⅱ) foliations developed in the fault zone indicate a right-lateral strike-slip-dominated displacement; and ⅲ) geological evidence and seismic data show that the Qingchuan fault is currently active as the main seismogenic fault dominated by a right-lateral strike-slip with an average slip rate of ca. 3-5 mm/yr. Our results demonstrate that the spatial change in slip sense along the LSTB from thrust-dominated in the central and southwestern sectors to right-lateral strike-slip-dominated in the northeastern sector is mainly caused by a change in the orientation of fault geometry from NE-SW to ENE-WSW along the LSTB.