Three-dimensional S-wave velocity structure in eastern Tibet from ambient noise Rayleigh and love wave tomography

We apply ambient noise tomography to continuous three-component broadband seismic data between January 1, 2008 and December 31, 2008 from the regional networks of 76 stations deployed by China Earthquake Administration. Ambient noise cross-correlations were performed to produce the Green’s functions of each station-pair. Within the period from 6 to 50 s, Rayleigh and Love wave dispersion curves were measured using the multiple filter analysis method. Then three-dimensional (3-D) S-wave velocity structures from the surface down to 70 km are inverted from both Rayleigh and Love wave dispersion results. The obtained S-wave velocity maps show strong lateral variations and correlate well with the distinct geological and tectonic features in the study area. The Sichuan basin displays low velocity in shallow depth due to thick sedimentary deposits but high velocity in the mid-lower crust; the eastern Tibetan plateau is clearly featured with a low-velocity zone in its mid-to-lower crust which is consistent with the crustal flow model proposed to explain the mechanism of uplift and pattern of deformation for the Tibetan plateau. Meanwhile, our results also exhibit that the crustal thickness decreased from the eastern Tibetan plateau to the Sichuan basin.