Ambient noise Rayleigh wave tomography in the northeastern Tibetan Plateau

Two years of seismic ambient noise observed by three provincial networks are used to estimate 2D Rayleigh wave group velocity and 3D shear wave velocity structure of northeastern Tibetan Plateau. Compared with traditional surface wave tomography, ambient noise tomography may provide refined structure of the crust and uppermost mantle. Low group velocities of 8 s and 10 s periods coincide with sedimentary layer and crystalline basement, while the high velocity zones denote igneous cores of the major mountain ranges. Qilian mountain and Qinling mountain show high velocity, but Qaidam basin, Hexi corridor of Gansu Province and western Ordos block show low velocity. 15 s and 20 s period group velocities represent the structure of middle crust, and the high velocity zones expand to north and east in 15 s period group velocity map. Whereas in the 20 s period group velocity map most areas show low velocity anomaly, which may correspond to the low velocity crustal layer revealed by previous studies. 30 s and 40 s period group velocity maps represent the velocity structure around the depth of Moho. The velocity maps show low velocity zones in Tibetan Plateau and high velocity towards the north and the east, suggesting that the crust is thick in Tibetan Plateau and thinned in the northern and the eastern studied areas. In addition, 3D shear velocity structure shows low velocity zone beneath Qilian orogen and Garze terrain. The two zones are connected by a lower crustal low velocity zone to the east of Qaidam basin, which may be a channel of northward material movement.