Characteristics of Cenozoic faults in Langshan area, Inner Mongolia: Constraint on the development of normal faults

The Langshan area, located on the northeastern margin of the Alxa block, was subjected to 3 deformation stages during the Cenozoic, which produced thrust faults formed by NW-SE compression in the late Miocene, left-lateral strike-slip faults caused by NNE compression and active normal faults in the late Cenozoic. Based on peripheral Cenozoic structures around the eastern Alxa margin, the authors infer that these Cenozoic faults were related to the gradual propagation of northeast Tibetan Plateau and the readjustment of the stress field. The Langshan piedmont fault zone is now at a stage of linkup, which is compatible with the constant-length fault model with the highest slip rate in the central part. The slip rate from Holocene seems to tend to become lower relative to the slip rate since late Pleistocene. Combined with the focal mechanisms as well as geometries and kinematics of faults in and around the Alxa block, the authors tentatively propose that the Hetao-Jilantai basin and the Yinchuan basin are two different extensional basins linked by a transfer zone, in which nearly NNE-trending dextral faults are developed. The Mw >5 earthquakes within the transfer zone probably occurred on the steep dextral faults as the result of regional SW-NE compression.