Characteristic of crustal structure beneath the rifts in southern Tibetan plateau

The method of 2-D travel time inversion, which can be applied to determining 2-D velocity structure and interfaces simultaneously, is used in this paper to reprocess the data of Paiku Co-Pumoyingcuo seismic profile across the Nyima- Tingri rift and Shenzha-Dinggye rift. P-wave velocity structure and interfaces beneath the profile are obtained. The interfaces in the crust near Tingri and Dinggye which are located on rifts have a tendency to uplift, and velocities of middle and lower crusts are high. Low velocity layer in upper crust has an offset. Compared with the distribution of the earthquakes in this region, it is speculated that normal faults near Tingri and Dinggye extend to the upper mantle. Apparently it is affected by deep material: the uplift of mantle causes partial melting in the crust, thus the thickness of crust in this area becomes thin, and tension failures occur in this region easily. On the basis of the characteristics of the earthquakes' distribution and the structures of the crustal velocity and interfaces, materials from the mantle still uplifts and the failures are still active.