Crustal Thickness and Poisson’s Ratio in Tianshan Region from Receiver Functions

The structure and physical properties of the crust in the Tianshan region are important for studying the tectonic evolution process within the Tianshan crust. We extracted the receiver functions by collecting the teleseismic waveform from 43 permanent and temporary stations in the Tianshan region (40–46° N, 78–92° E), and obtained the crustal thickness and Poisson’s ratio by using the H–κ–c stacking method to eliminate the effects of the anisotropy and dipping interface in the crust. The results from the H–κ–c stacking method are more robust than those obtained from traditional H–κ stacking. The crustal thickness in the study area ranges from 38 to 62 km with an average of 51 km. The overall crustal thickness is found to be thicker at the Tianshan Mountains but thinner in the basins to the north and south. It is assumed that these features are related to the subduction of Tarim Basin and Junggar Basin beneath the Tianshan Mountains, where insertion and subduction occurred, resulting in crustal shortening and thickening. The Poisson’s ratio in most areas of the Tianshan Mountains ranges from 0.23 to 0.27, close to the average for continental crust. In the contact zone between the southern margin of Junggar Basin and Tianshan Mountains and from the northern margin of Tarim Basin to the western part of the Tianshan Mountains, the Poisson’s ratio reaches as high as 0.3. Based on the velocity structure, electrical conductivity, density, and heat flow study, the higher Poisson’s ratio near the contact zones is probably related to partial melting of the mass with low melting point from the basins due to the subduction. The Tianshan Mountains and Tarim Basin show a clear unbalanced isostatic gravitational state.