Computation of the present-day strain rate field of the Qinghai-Tibetan plateau and its geodynamic implications

Many researchers have calculated strain rates from the same GPS measurement data and obtained different results. In this paper, we introduce the Kriging method in geo-statistics to the study of GPS velocity field. Interpolating the scattered GPS velocity data of the Qinghai-Tibetan plateau and its adjacent areas to grid point values by the Kriging method, we calculate the strain rates from these nodal values of all elements similar to derivatives of shape functions(essential Lagrange interpolation function) in the finite element algorithm. and obtain the distribution of the strain rate field in the Qinghai-Tibetan plateau. The results show that the main part of the Qinghai-Tibetan plateau is in the state of compression in north-south direction, and of extension in the orientation of east-west. On the contrary, in the eastern part of Qinghai-Tibet, the strain rate behaves compressively in east-west and extension in north-south trending. The orientations of principal strain rates are consistent with those of the P axis and T axis in focal mechanisms. The high values of maximum compressive principal strain rates are located in the Himalayan main boundary thrust zone (MBT) and its adjacent regions. The maximum extensional principal strain rate is higher than that of the compressive one in some regions of the interior of the Qinghai-Tibetan Plateau, so the region is in the state of extension. Also, the surface dilation strain rate shows that it is in the state of surface compression in the Himalayan and its surrounding areas, and it is in the state of surface extension in the interior of the Qinghai-Tibetan Plateau. The distribution of maximum shear strain rates clearly shows the patterns of some main active fault zones. The result of the strain rate in this study suggests that the contemporary tectonic strain of Tibet inherits the long term geological deformation.