Waveform inversion of S-wave velocity model in the central Qiangtang in North Tibet and its geological implications

The Qiangtang basin is the largest Mesozoic-to-Cenozoic marine sediment basin in China. The central metamorphic belt in central Qiangtang divides it into South Qiangtang basin and North Qiangtang basin. This study conducted a series of teleseismic receiver functions across the Qiangtang basin. The teleseismic data came from a temporary seismic array in Qiangtang basin. High-quality receiver functions were picked up from 738 teleseismic traces of 338 teleseismic events recorded by 27 stations along 88. 5 degrees E in 2009-2010. 1-D S-wave velocity model was calculated by the nonlinear inversion of conjugate gradients algorithm for the complex spectrum ratios of receiver function. Because the method made full use of amplitude ratio between the vertical and radial components of the receiver function in time domain, the final model from the method is completely independent of the initial model parameters. The velocity model indicated that the Moho beneath Qiangtang area rises slowly from south to north. The South Qiangtang basin has an average Moho depth of 68 km. In the North Qiangtang basin the average Moho depth is 60 km, which are in accordance with H-kappa stack and deep seismic reflection results. There is a continuous low velocity layer beneath the North Qiangtang basin. While in the South Qiangtang basin the low velocity area is discontinuous, which causes hot springs along thrust faults. The sedimentary thickness was determined by deep seismic reflection and Poisson's ratio. There is one large sedimentary basin in the South Qiangtang basin and two in the North. Geological survey suggested that the two depressions in North Qiangtang, Longwei Co and Baitan Lake, have pretty good outlook in petroleum exploration.