Understanding the structure of crust and shallow upper mantle beneath western Tibet through the joint inversion of Rayleigh wave group velocity dispersion with interpolated receiver functions

We present the 3-D shear wave velocity variationin the crust and upper mantle structure of western Tibet using a joint inversion of Rayleigh wave group velocity dispersion and interpolated receiver function. The lateral sampling of the receiver function and the surface wave dispersion is equalized by the interpolation scheme. This new method of spatial interpolation eliminates difficulties caused by back azimuthal variation in the receiver function. We have jointly inverted these interpolated receiver functions with the Rayleigh wave group velocity dispersions obtained from the earthquake and ambient noise tomography to map the tectonic structure of western Tibet. The study reveals remarkable variation of the seismic characteristics in the crust and shallow upper mantle of western Tibet. The mapped Moho depth is ~74 km in the northern part of the plateau, whereas it is ~69 km in the southern part. A thick mid-crustal slow-velocity zone from ~10km up to ~40 km depth has been observed, which could be attributed to partial melt. A noteworthy finding is the variation in slower crustal velocity between the south and north of the Lhasa Block (LB). We interpret this as the Indian crust that has been underthrusted beneath the Tibetan plateau, and the northern limit of the Indian lithosphere extends to the southern part of the LB.