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Abstract:
We present a three-dimensional model of shear wave velocity for the upper mantle of China and the surrounding region by analyzing 50,338 vertical component multi-mode Rayleigh wave seismograms, recorded at 144 permanent and more than 300 temporary broadband stations in and around China. The procedure involves combination of 1-D path average models obtained by modeling each Rayleigh waveform up to the 4th higher mode in a tomographic inversion scheme. The dense station network and the use of multi-mode analysis help to achieve a lateral resolution of a few hundred kilometers down to 400 km depth. The seismic lithosphere, as it is defined by the crust and the high velocity mantle lid, is to the first order thin in east China and thick in the west, with a high velocity lid extending down to about 200 km depth beneath much of the Tibet–Pamir plateau. Beneath India, the thickness of the seismic lithosphere gradually increases from ~ 100 km in south India to more than 150 km in north India, where it underthrusts the Tibetan plateau to approximately the Jinsha River Suture. High velocity lid extending down to 100–150 km depth is also observed in the Tarim basin, Sichuan basin and Ordos block. In the eastern part of the North China craton the seismic lithosphere is probably close to or thinner than 70 km. Adjacent to these areas, the high velocity lid in the eastern Yangtze craton and South China fold system extends down to 70–80 km depth. A large-scale subhorizontal high velocity body is observed at depths of 150–350 km beneath the entire east China cratonic areas. This high velocity body might be the remnant of a delamination process which resulted in the decratonization of the North China and the Yangtze cratons.
