Joint Inversion Of Receiver Functions And Gravity Data And Its Application In The Northeastern Margin Of The Tibetan Plateau

The crustal thickness (H) and the wave velocity ratio (?) are two important parameters to reveal the structure and material composition of the crust, thus benefitting in providing evidence for the studies of crustal deformation and dynamics.The H-? stacking technique in receiver function analysis is popular for estimating H and ? parameters, and has been widely applied in many places. However, in practical applications, complicated structure beneath some seismograph stations and poor quality of seismic waveform data will result in unclear multiple reflection phases of receiver function and the uncertainty solution of H-? stacking. This dissertation proposes an improved approach for joint inversion of receiver function and gravity data, to estimate crustal thickness and wave velocity ratio parameter, and to reduce uncertainty and to improve the accuracy and efficiency of inversion. This approach will provide technical support for revealing regional crustal structure and material composition.The main achievements of this dissertation are as follows:1. This dissertation presents a simplified and improved algorithm for the joint inversion of receiver function and gravity data, including simplification of gravity anomaly composition, initialization crustal thickness and wave velocity ratio, and improvement of the likelihood estimation algorithm of gravity inversion. These improvements lead to H-? stacking spectrum focused and clear relatively, so as to reduce the uncertainty of inversion and improve picking efficiency and accuracy of the crustal thickness and velocity ratio parameter.2. The theoretical model tests verify the effectiveness of this approach.Parameter tests show that the Vp value, the sliding window size and grid spacing have little effect on the joint inversion, while the initial value of crustal thickness and velocity ratio have great influence on the joint inversion. So, it is necessary to set reasonable initial values of the crustal thickness and velocity ratio generally for joint inversion.3. The actual data test in the northeastern margin of Tibet Plateau also proves the effectiveness of the presented approach. The results show that the average crustal thickness of Alashan block and Ordos block is about 45km, and the Poisson's ratio is about 0.29, which indicates that the crust is mainly composed of mafic rocks. The average crustal thickness of the Tibet Plateau is about 56km and the Poisson's ratio is about 0.23, which indicates that the crust is mainly composed of felsic rocks. And the average crustal thickness of the intersection of the three blocks is about 49km, the Poisson's ratio is around 0.27, which indicates that the crust is mainly composed of felsic and mafic rocks. The study shows that there is a negative relationship between the crustal thickness and Poisson's ratio which supports the thickening of the upper crust in the northeastern margin of the Tibet plateau.