Crustal Anisotropy in Central Tibetan Plateau: Inferred from Multi-taper Receiver Functions

Tibetan Plateau is the largest and highest plateau on Earth. Evidence has shown that the plateau formed as a result of the collision of the Indian subcontinent with Eurasia. The crust may have thickened by shortening, or a large-scale shallow thrusting may have underplated the plateau. Amplitude and distribution of crustal anisotropy have profound implications on the history of continental deformation. In this study, we first investigated the back-azimuth dependence of P-s converted phases using multi-taper receiver functions (RFs) (Bianchi et al, 2010). We analyzed teleseismic data for 26 temporary broadband stations in ASCENT experiment locating in central Tibet. We stack receiver functions after a moving-window moveout correction. Major features of RFs include: 1) P-s arrival at 8~9s on the radial components, suggesting a crust thickness of 70~80km in the study area; 2) two-lobed intracrustal P-s phases with clear polarity reversal are largely observed on the transverse RFs, which indicate tilted symmetry-axis anisotropy. To study the geometry of anisotropy beneath each station, we compare synthetics generated with one-dimensional anisotropic reflectivity method (Levin and Park, 1997) and the observed RFs, and fit major features by forward modeling. Mapping the amplitude and distribution of crustal anisotropy in the study area will provide important information on the evolution of Tibetan plateau. Bianchi, I., J. Park, N. P. Agostinetti, V. Levin, Mapping seismic anisotropy using harmonic decomposition of receiver functions: an application to Northern Apennines, Italy, J. Geophys. Res., 115, B12317, doi:10.1029/2009JB007061, 2010. Levin, V., and J. Park, P-SH conversions in a flat-layered medium with anisotropy of arbitrary orientation, Geophys. J. Int., v131, pp 253-266, 1997.