Dense-array ambient noise tomography of the eastern Tibetan Plateau: a high-resolution model of the crustal low-velocity zone and its tectonic evolution implications

The Cenozoic collision and convergence of the Indian and Eurasian plates have resulted in north–south crustal shortening, crustal thickening, and overall surface uplift of the Tibetan Plateau. Accompanying the outward expansion of the plateau, lateral tectonic extrusion promoted its rapid uplift and further crustal thickening. The Tibetan Plateau underwent eastward expansion from the Late Miocene to the Early Pliocene. We collected continuous waveform data recorded by dense seismic arrays deployed across the eastern Tibetan Plateau and constructed a high-resolution 3-D S-wave velocity and azimuthal anisotropy model using ambient noise tomography. The model delineates in detail the upper and lower boundaries of the low-velocity zone (LVZ) in the mid-lower crust. The spatial distribution of the LVZ is consistent with regions characterized by pronounced lateral extrusion and deformation in the eastern Tibetan Plateau. Furthermore, the LVZ exhibits strong azimuthal anisotropy, providing direct evidence for the pathways of ductile crustal flow. The high-resolution model reveals correlations between variations in LVZ thickness and surface topography, Moho depth, and contemporary GPS observations. These findings indicate that ductile crustal flow functions as an active mechanical layer and plays a dominant role in surface uplift, crustal thickening, and ongoing deformation across the eastern Tibetan Plateau. The large-scale deformation of the eastern Tibetan Plateau, which accounts for surface uplift and crustal thickening, is generally modeled as being driven by ductile crustal flow. As an active tectonic driving layer, this flow diverges into three branches extending eastward and southeastward along the Qilian, Songpan–Ganzi, and Qiangtang Terranes, further triggering lateral extrusion and deformation of the eastern Tibetan Plateau.