Preliminary Study of Crust-Upper Mantle Structure of the Tibetan Plateau by Using Broadband Teleseismic Body Waveforms

As part of a joint Sino-U.S. research project to study the deep structure of the Tibetan plateau, 11 broadband digital seismic recorders were deployed on the plateau for one year of passive seismic recording. In this report we use teleseimic P waveforms to study the seismic velocity structure of crust and upper mantle under three stations by receiver function inversion. The receiver function is obtained by first rotating two horizontal components of seismic records into radial and tangential components and then deconvolving the vertical component from them. The receiver function depends only on the structure near the station because the source and path effects have been removed by the deconvolution. To suppress noise, receiver functions calculated from events clustered in a small range of back-azimuths and epicentral distances are stacked. Using a matrix formalism describing the propagation of elastic waves in laterally homogeneous stratified medium, a synthetic receiver function and differential receiver functions for the parameters in each layer can be calculated to establish a linearized inversion for one-dimensional velocity structure. Preliminary results of three stations, WNDO, TUNL and XIGA located in central, northern and southern plateau are given in this paper. The receiver functions of all three stations show clear P − S converted phases. The time delays of these converted phases relative to direct P arrivals are: WNDO 7.9 s (for NE direction) and 8.3 s (for SE direction), TUNL 8.2 s, XIGA 9.0 s. Such long time delays indicate the great thickness of crust under the plateau.