Using OBS teleseismic receiver functions to invert lithospheric structure-A case study of the southwestern subbasin in the South China Sea

Due to the particular seafloor environment and special outer mechanical structure of the ocean bottom seismometer (OBS), there are some problems which have not been solved in the lithospheric structure inversion using OBS teleseismic receiver functions. Based on the analysis of these problems, we combined the Fourier transform and wavelet analysis to suppress the non stationary noise to obtain a better signal-to-noise ratio and clearer seismic phases recorded by the OBSs at the southwestern subbasin in the South China Sea (SCS). The equipment is broadband OBS of I-4C type produced by the Institute of Geology and Geophysics, Chinese Academy of Sciences. We then inverted the lithospheric structure by applying receiver functions to the teleseismic data recorded at the southwestern subbasin of the SCS successfully. The results show that it is feasible to use receiver functions for the inversion of lithosphere structure based on the passive observation data by OBS, in which the key is to suppress the non-stationary noise. The Moho depth in the southwestern subbasin of the SCS is 10 similar to 12 km with crust thickness of 6 similar to 8 km. The shallow crust is a low velocity layer with sediment thickness 1 similar to 2 km which consists of sediment and volcanic clastic breccia produced by magma eruption after spreading cessation. In the spreading axis center there is a low S-wave velocity zone at the depth of 6 km to 12 km above Moho. We interpreted it as the result of partial melting of the lower crust or the presence of a magma chamber. In the same area at the depth of 17 km to 30 km the vertical S-wave velocity gradient is negative. We interpreted it as the result of hot magma supply upward in the mantle.