Crustal deformation characteristics and tectonic implications on the northeastern margin of the Tibetan Plateau

Abstract

This study utilizes continuous waveform data from 50 portable stations and 38 permanent stations deployed on the northeastern margin of the Tibetan Plateau. Using ambient noise cross-correlation, we obtained Rayleigh wave phase velocities for periods ranging from 1 to 35 s and subsequently inverted these data to obtain the 3D azimuthally anisotropic shear wave velocity model. The results indicate a clear zonation of azimuthal anisotropy characteristics within the study area. Using the Haiyuan-Liupanshan fault zone as the dividing line, the shallow crust of the eastern Ordos block exhibits weak anisotropy due to sedimentary layer, with fast wave direction-oriented NS. In the middle and lower crust, the fast wave directions are oriented NE. On the western side, the shallow crust exhibits fast wave directions consistent with the regional tectonic orientations. The middle and lower crust exhibits two dominant fast wave directions influenced by regional principal tectonic stress: NE-SW, primarily distributed at the eastern end of the Haiyuan fault zone, and NWW-SEE, mainly found near the northern side of the North Qinling fault zone. These two differing directions result in the left-lateral strike-slip movement of the Haiyuan fault zone and the clockwise rotation of the Longzhong Basin. The average azimuthal anisotropy results show significant tectonic influence on the shallow parts of the northeastern margin of the Tibetan Plateau, with consistent deep fast wave directions in the Haiyuan-Liupanshan area, suggesting a possible coupling deformation mechanism. The North Qinling fault zone area shows significant changes in anisotropy amplitude and fast wave directions around 45 km depth, indicating a decoupling layer and discontinuous deformation mechanisms between the upper and lower crust.