The ∼430-km-long, east−west-striking northern West Qinling fault is seismically active and serves as a critical tectonic bridge, facilitating strain transfer between the contractional northeastern margin of the Tibetan Plateau and the extensional North China Craton. Using high-resolution Satellite for Earth Observation (SPOT) imagery in combination with field observations, this study analyzes geomorphic markers, geologic evidence, and geodetic constraints on left-lateral slip deformation along this structurally complex fault system and examines strain transfer between strike-slip faults in Northeast Tibet. The western segment (∼120 km) exhibits diagnostic left-lateral geomorphic signatures, with four distinct classes of river channel offsets measuring 3500−4100 m, 340−430 m, 75−130 m, and ∼35 m. These cumulative displacements contrast sharply with the subdued morphology along the central segment (∼160 km), where Neogene basin deformation records a Pliocene compressional phase, as evidenced by an angular unconformity between Quaternary deposits and the underlying Neogene red strata. The eastern segment (∼150 km) displays brittle deformation textures, including fault breccias and ultracataclasites, but lacks evidence of significant Holocene activity. Cumulative offsets (∼4000 m) along the western segment align with a long-term low slip rate of 0.8−1.7 mm/yr, assuming deformation initiated at 5 Ma or 2.4 Ma. GPS velocity field corroborates a slow slip rate, showing ∼1 mm/yr sinistral motion in the west and negligible activity in the east. Regionally, the northern West Qinling fault and active faults in West Qinling form a structural continuation of the active East Kunlun sinistral fault system and extend eastward through the southern Weihe graben into East Qinling. Slip transfer occurred through fault bending and bifurcation. By integrating surface deformation with the subsurface velocity structure, we propose a layered-flow model wherein the eastward extrusion of the materials from beneath the Tibetan Plateau through the Qinling belt induces mechanical decoupling between upper-mantle flow and brittle crustal deformation. This vertically partitioned rheology could explain the observed disparity between surface fault kinematics and subsurface mass transport dynamics.
Zhang et al. (Tue,) studied this question.