Northeastern Tibet is an important place for understanding the growth of the Tibet plateau and its eastward extrusion. To distinguish the model responsible for the development of northeastern Tibet, we have analyzed Rayleigh wave data recorded by the Northeast Tibet Seismic (NETS) array and applied the Two-Plane-Wave (TPW) tomography method to compute average and 2-D phase velocities.

Vertical component seismograms from 70 events at 35 stations were filtered at 17 center frequencies with a narrow bandwith of 10 mHz. Average phase velocity varies from 3.21 km/s at 20 s to 3.84 km/s at 100 s. Compared to the average phase velocities in southeastern Tibet, these values are higher in the period range of 20-50 s and lower at longer periods, probably indicating a faster and thinner crust and slower upper mantle in northeastern Tibet. We also obtained average phase velocities in three sub-regions which are separated by the Kunlun and Haiyuan fault.

The northernmost subarea including part of the Odos block is characterized with the highest phase velocity while the area to the south of the Kunlun fault is the slowest in northeast Tibet. 2-D variation of phase velocity was calculated in the periods from 20s to 100s. The low velocity anomaly is imaged along and to the south of the Kunlun fault at each period. And relative high velocity is consistently imaged to the north of Kunlun fault. 3-D shear wave inversion was conducted to understand the crust and upper mantle structure from the obtained phase velocities. A relative low velocity zone is image beneath Kunlun fault in the lower crust and upper mantle. The mechanisms responsible for this low velocity zone will be interpreted to help understand the tectonic and the role of Kunlun fault playing in the rising of Northeast Tibet.