Mapping the upper mantle discontinuities beneath China with teleseismic receiver functions

We used teleseismic body waves recorded at stations of the Chinese Center of Digital Seismic Network to map the upper mantle discontinuities beneath continental China. The CRUST2.0 and an S -tomography model beneath each station were combined with the one-dimensional tracing method to convert time series of radial receiver functions to depth series. Clear signatures corresponding to the 410- and 660-km discontinuities (‘410’ and ‘660’) are visible at almost all of the stations. The average S velocity contrast of ‘410’ beneath the study area is close to the global average, but that for ‘660’ is smaller than the global average. The average depth of ‘410’ is 413 km, and the peak-to-peak topography is about 36 km, with regional depressions that correlate with the Datong quaternary volcano in northern China. The ‘660’ topography exhibits a peak-to-peak variation of about 43 km, and its average depth is 669 km; the depressions of the ‘660’ in northeastern, southeastern and northern China are well correlated with the past subduction around the Pacific Ocean and Philippine Sea. The width of the transition zone is also increased in the region with the deeper ‘660’. Our results would appear to indicate that there may be a low-velocity layer below a depth of approximately 600 km that may be the accumulated garnetite layer of an ancient crust above the ‘660’.