Surface wave dispersion across Tibet: Direct evidence for radial anisotropy in the crust
Recordings in western Tibet of Rayleigh and Love waves at periods less than 70 s from aftershocks of the 2008 Sichuan earthquake cannot be matched by an isotropic velocity model beneath Tibet. These intermediate-period Rayleigh and Love waves require marked radial anisotropy in the middle crust of Tibet, with the vertically polarized S-waves propagating more slowly than S-waves with horizontal polarization. The magnitude of anisotropy inferred using paths entirely within Tibet is slightly greater than that obtained previously from a tomographic inversion of a dataset covering a larger region. Anisotropy in the middle crust likely reflects deformation of the middle crust, and is consistent with the notion of mid-crustal flow and thinning of the crust.