In this study, I applied ambient noise tomography to continuous waveform data from 118 stations with broadband seismometers in northeastern Xizang in the time window of 2011–2012. The 3D S-wave velocity in the depth of 0–50 km was obtained. The results reveal distinct velocity anomalies at various depths, shedding light on the complex crustal and upper mantle structures and their dynamic evolution in this region.

At a depth of ~10 km, significant low-velocity anomalies are observed in the Qaidam Basin, the western part of the Ordos Block, and the Hexi Corridor, while the Qilian Mountains exhibit high-velocity anomalies. The low-velocity anomaly in the Qaidam Basin is likely associated with thick sedimentary layers and fluid saturation, whereas the low-velocity anomalies in the western Ordos and the Hexi Corridor may be related to local sedimentary basins and fault structures.

At a depth of ~30 km, the Qaidam Block transitions from a low-velocity to a high-velocity anomaly, indicating a more stable lower crustal structure. In contrast, the Songpan-Ganzi Block shows significant low-velocity anomalies, which may be attributed to partial melting in the middle to lower crust. The Qilian Block gradually shifts from high to low velocity, reflecting the complex processes of crustal thickening and tectonic deformation in this region.

At a depth of 50 km, the western part of the study area primarily reflects the velocity distribution of the lower crust, while the northeastern part reveals the characteristics of the upper mantle.

Further analysis indicates the presence of distinct low-velocity layers in the middle to lower crust of both the Songpan-Ganzi Block and the Qilian Block. The low-velocity anomaly in the Songpan-Ganzi Block is likely caused by the viscous flow of mid-lower crustal materials. The low-velocity layer in the Qilian Orogenic Belt may be related to crustal shortening and thermal weakening resulting from the collision between the Xizang Block and its surrounding blocks. The existence of these low-velocity layers provides critical insights into the mechanisms of crustal deformation in the northeastern margin of the Qinghai-Xizang Plateau.

The findings of this study offer important geophysical evidence for understanding the crust-mantle deformation characteristics in the northeastern margin of the Qinghai-Xizang Plateau, contributing significantly to unraveling the dynamic processes of plateau uplift and expansion.