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We present high‐resolution 3D images of the crustal S‐wave velocity structure beneath northeastern Tibet, via ambient noise imaging techniques. The data come from continuous recordings taken in one year by a seismic array consisting of 366 broadband stations in the study region. The results show a substantial and pervasive middle crust low‐velocity structure (<3.4 km/s) beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The growth of the northeastern Tibetan Plateau in the study region is manifested in its northeastward expansion and thickening driven by crustal channel flow, accompanied with upper crust shortening. Plain Language Summary: The growth mechanisms of the Tibetan Plateau (TP) have been considered controversial for decades. Expansion of the northeastern TP and the interaction with its peripheral area have become of major interest to researchers. In this study, we present a high‐resolution 3D image of the crustal S‐wave velocity structure beneath this area by analyzing the continuous ambient noise data recoded by a dense seismic array via ambient noise imaging techniques. The results show a substantial and pervasive middle crust low‐velocity structure beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The channel flow slows down gradually with its outward protrusion. The upper and lower crust is decoupled. In addition to the crustal channel flow, upper crust shortening takes part in the growth of the northeastern Tibet. Key Points: High‐resolution 3D crustal shear‐wave velocity images beneath the northeastern Tibetan margin via ambient noise imaging techniquesSubstantial and pervasive middle crustal channel flow is found beneath the northeastern TibetThe northeastward expansion of the northeastern Tibet is driven by crustal channel flow, accompanied with upper crust shortening [ABSTRACT FROM AUTHOR]

We present high‐resolution 3D images of the crustal S‐wave velocity structure beneath northeastern Tibet, via ambient noise imaging techniques. The data come from continuous recordings taken in one year by a seismic array consisting of 366 broadband stations in the study region. The results show a substantial and pervasive middle crust low‐velocity structure (<3.4 km/s) beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The growth of the northeastern Tibetan Plateau in the study region is manifested in its northeastward expansion and thickening driven by crustal channel flow, accompanied with upper crust shortening. Plain Language Summary: The growth mechanisms of the Tibetan Plateau (TP) have been considered controversial for decades. Expansion of the northeastern TP and the interaction with its peripheral area have become of major interest to researchers. In this study, we present a high‐resolution 3D image of the crustal S‐wave velocity structure beneath this area by analyzing the continuous ambient noise data recoded by a dense seismic array via ambient noise imaging techniques. The results show a substantial and pervasive middle crust low‐velocity structure beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The channel flow slows down gradually with its outward protrusion. The upper and lower crust is decoupled. In addition to the crustal channel flow, upper crust shortening takes part in the growth of the northeastern Tibet. Key Points: High‐resolution 3D crustal shear‐wave velocity images beneath the northeastern Tibetan margin via ambient noise imaging techniquesSubstantial and pervasive middle crustal channel flow is found beneath the northeastern TibetThe northeastward expansion of the northeastern Tibet is driven by crustal channel flow, accompanied with upper crust shortening [ABSTRACT FROM AUTHOR]

• 1. Ambient noise tomography with topography correction is used to study the 3D crustal velocity structure. • 2. The S-wave velocity structure controls the downward stretch of the Longmen Shan faults. • 3. The expansion of the middle-lower crustal low-velocity layer is responsible for the growth of eastern Tibet. The Longmen Shan (LMS) fault zone is located on the eastern margin of the Tibetan Plateau and is a representative area for studying the eastward growth of the plateau. In this study, we present a 3-D crustal S-wave velocity structure beneath the LMS fault zone and its adjacent regions with a lateral resolution of ∼ 10 km down to a depth of 25 km from data recorded at 57 stations over one year using seismic ambient noise imaging techniques. The high and steep topography of the LMS is considered when building the high-resolution image of the upper and middle crust. The imaging provides further evidence for the high-angle listric characteristics of the LMS faults south of Beichuan, and the feature disappears toward the north, indicating differences in deformation from south to north. The structural characteristics are well correlated with the aftershock distribution and the rupture of the Wenchuan earthquake, which indicate a change in the mechanism from mostly thrust in the south to mostly strike slip in the north. The velocity structure controls the downward stretch of the faults. The results support that crustal channel flow is responsible for the growth of eastern Tibet. The eastward movement of the weak crustal material was blocked by the hard crust surrounding the Minshan uplift, resulting in great differences in the velocity structures and fault properties south and north of Beichuan. [ABSTRACT FROM AUTHOR]

The Yinchuan-Hetao (YC-HT) graben is the boundary zone between the Ordos and the Alax blocks in NW China, which shows tectonic patterns distinct from the Haiyuan arcuate and Liupanshan thrust belts to the south. As a Cenozoic rift, the YC-HT graben originated from back-arc spreading related to westward subduction of the western Pacific, but its deformation and development may have been more influenced by the extension of the northeastern Tibetan Plateau (NETP) since the Quaternary. To investigate the dynamics of deep deformation of the YC-HT graben and adjacent regions, we apply the receiver function method to obtain the seismic structure in this area. Our results show that the depth of the Moho beneath the YC-HT graben is ∼50 km and significantly greater than that beneath the Alxa and Ordos blocks. The crust of the Ordos block is characterized by a layered structure, and the intracrustal structure below the YC-HT graben has undergone significant deformation. The Vp/Vs ratio in a local area of the western Hetao graben is as high as ∼1.9. By combining our observations with previous geophysical and geological studies, we speculate that the influence of NETP expansion has reached the YC-HT graben at depth. Meanwhile, the upper and lower crust experienced different deformation modes in this area, which manifested as elastic deformation in the upper crust and plastic deformation in the lower crust. [Display omitted] • Crustal velocity discontinuity structure and Vp/Vs ratios are obtained in the northwestern border of the Ordos, NW China. • Thickened crust and high Vp/Vs anomalies in the crust dominate the Yinchuan-Hetao graben. • Upper and lower crust beneath the Yinchuan-Hetao graben have undergone extensional and thickening deformation respectively. [ABSTRACT FROM AUTHOR]