Crustal azimuthal anisotropy and deformation beneath the northeastern Tibetan Plateau and adjacent areas: Insights from receiver function analysis

Abstract

We present crustal azimuthal anisotropy measurements at 246 stations by fitting the sinusoidal moveout of P-to-S receiver functions to infer crustal deformation field in the northeastern (NE) Tibetan Plateau and adjacent areas. The dominant orientation of the observed crustal anisotropy shows a systematic spatial variation: NW-SE in the NE Tibetan Plateau and western Alxa Block, nearly NE-SW in the eastern Alxa Block and Yinchuan-Hetao Graben, and E-W in the eastern portion of the Western Qinling Terrane. The magnitude of crustal anisotropy varies from 0.15 to 0.75 s with an average of 0.36 ± 0.11 s. Fault parallel crustal anisotropy with large magnitudes observed in the NE Tibetan Plateau provides independent constraints on the lateral extent of the deformation zone associated with the faults. The observed spatial distribution of crustal anisotropy, when combined with previous crustal velocity and Poisson's ratio measurements, implies that channel flow in the middle-to-lower crust is unlikely to exist beneath the NE Tibetan Plateau. The main characteristics of crustal anisotropy observed in the western Alxa Block are similar to areas affected by the Indo-Eurasian collision, while those observed in the eastern Alxa Block are comparable to the stable North China Craton.