Imaging the Mantle Lithosphere below the China cratons using S-to-p converted waves

Abstract

We used S-to-p converted waves from over a thousand seismic stations of the permanent Chinese National Seismic Network to study the large scale structure of the mantle lithosphere beneath the cratons in China. To avoid possible sidelobes of the Moho caused by the deconvolution in the S-receiver function method, we skipped the deconvolution and used the SV onset time as reference time instead of the time of the deconvolution spike. With this new method the lithosphere-asthenosphere boundary (LAB) is observed near 80 km depth below both the North and the South China cratons. However, at the north-eastern margin of the Tibetan Plateau the LAB is observed at about 160 km depth, smoothly shallowing towards the west and abruptly ending at the western end of the North China Craton. This structure is not visible in traditional S-receiver function data because it is overwhelmed by Moho sidelobes. There is no indication of a deeper (near 200 km) cratonic lithosphere-asthenosphere boundary in the other parts of the China cratons as it is observed in other cratons. We hypothesise that at the north-eastern margin of the Tibetan Plateau the original thickening of the lithosphere towards the craton is preserved whereas in most parts of the North and South China Cratons the lower part of the lithosphere is removed by some mechanism. The Moho is well observed. It deepens from 30 to 40 km at the sea shores in the east to 60–70 km below eastern Tibetan Plateau.