Low Velocity Layer Investigation in Central Qiangtang in North Tibet and Its Dynamic Implications

In order to investigate the distribution characteristics of the low velocity layer in the central Qiangtang basin, this study conducted the TITAN-Ⅰ teleseismic receiver functions across the Qiangtang basin. And the signal-to-noise ratio of the receiver function was improved by the phase filtering technique in the time frequency domain. Finally, the one-dimensional S wave velocity structure in the depth of 100 km below each station is obtained by the nonlinear inversion of conjugate gradients algorithm for the complex spectrum ratios of receiver function. The results show that the phase filtering method in the time frequency domain can significantly improve the signal-to-noise ratio and make the one-dimensional S wave velocity structure of the subsequent inversion more reliable. The Moho depth of the Qiangtang basin is 58 ±6 km, and where has a higher Poisson's ratio. The low velocity layer in the mid-lower crust is widely distributed. The transverse discontinuity is discontinuous, and the depth is between 20 and 30 km, the thickness of the layer is 6-12 km, the shear wave velocity is 3.4±0.1 km/s. In some areas, there is a thin layer of 4 km thin layer in the mid-upper crust with a depth of 10 km. The low velocity layer in the mid-lower crust of the Qiangtang basin is caused by the deep mantle derived magma upwelling along the tectonic weak zone, resulting in partial melting in the mid-lower crust and upper mantle.