The Format Criterion Of Doctoral Dissertation Of CUP

Mapping seismic structures of sedimentary basins is of great importance to better evaluate energy resources and seismic hazards.In this study,we develop a joint Bayesian Monte Carlo nonlinear inversion method that utilizes the complementary nature of Rayleigh wave phase velocity,Rayleigh wave particle motion,and teleseismic P and coda wave in responding to sedimentary structures.Synthetic tests demonstrate that the joint inversion can retrieve the input sedimentary structures better than inversions with surface or body wave data alone.We apply the method to two broadband stations inside the Songliao Basin in northeast China to invert for sedimentary structures beneath the two stations.We verify our results by successfully isolating the Moho P-to-S conversion from sediment reverberations in regular receiver functions with a wavefield-downward-continuation technique.We further demonstrate that we can extend our method to single station inversion by excluding the Rayleigh wave phase velocity in the inversion.As the Rayliegh wave phase velocity are extracted through the ambient noise correlation technique,and stacking is an important method to enhance the SNR of the signals.Nowadays,the time-frequency domain phase weighted stacking(tf-PWS)technique based on the S transform has been functions(EGFs)derived from ambient noise data,mainly due to its superior power in enhancing weak signals.Questions such as the induced waveform distortion and the feasibility of phase velocity extraction are yet to be thoroughly explored.In this study,we also investigate these issues by conducting extensive numerical tests with both synthetic data and USArray TA ambient noise data.We find that the bias of the measured phase velocity associated with waveform distortion caused by the tf-PWS employed in stacking emprical Green'smethod is less than 0.1%,sufficiently small that the measured phase velocities can be safely used in regular surface wave tomography.We also find that tf-PWS implemented with a time inversion S transform(IST)tends to cause large waveform distortion.The extracted phase velocities are systematically larger than those measured from linearly stacked ones,and the discrepancy can reach as much as ~0.4% at periods larger than 60 s.If tf-PWS is used in stacking EGFs,then frequency IST is preferred to transform the stacked S spectra back to the time domain for the stacked EGFs.Then we systematically apply the tf-PWS and joint inversion techniques to the Wombat array,deployed in south east Australia.To verify the accuracy of the inverted model,sedimentary depths from four boreholes are used.On average,the differences between the inverted sedimentary depths and the drilled depths are 198 m.Based on the fact that the locations of the four boreholes are not completely overlap with the stations,that differences are acceptable.Besides,the bounderies between the high and low velocity anomalies outlines are consistent with the bounderies of the basin and orogenies,which further imply the inverted shallow structure are reasonable.