Stratified Crustal Anisotropy From Receiver Function

Continental dynamics has been the leading direction of the research in the present-day solid earth sciences. In spite of the wide range of issues involved in the continental dynamics, its core problem is to study the deformation and dynamic mechanism of the continent. The anisotropy of the earth medium is closely related to its mineral composition,temperature and pressure, stress state and deformation history. The anisotropic parameters of the earth medium have become an important basis for inferring the deformation of different layers in the subsurface of the Earth.Early studies suggested that the anisotropy of the earth’s interior is mainly derived from olivine lattice-preferred orientation formed by the mantle plastic flow under high temperature and high pressure, and it is mainly manifested in the upper mantle or top of the upper mantle, and the crustal anisotropy could be ignored. In recent years, however, the results from the P-wave receiver function have shown that not only the crustal anisotropy can not be ignored, but also the anisotropy of the different layers of the crust and its mechanism are not the same. Therefore,the study on the anisotropy of the crust is not only important for the determination of the anisotropy of the lithospheric mantle, but also is of great significance for understanding the deformation style of different layers of the crust.The teleseismic receiver function has become an important way to study the crustal anisotropy. However, in view of the complexity of the crustal medium, how to extract anisotropic parameters at different depths from the receiver function is still a subject to be solved.Study of crustal anisotropy from teleseismic receiver function is faced with two problems: 1) the scattering wave field from the crustal media and its laterally inhomogeneous structures often causes interference hard to be tolerated for extracting the anisotropic parameters from the receiver function; 2) study of the crustal anisotropy from receiving function relied on its complete orientation of receiver function, but it is often difficult due to the lack of azimuth of the receiver function caused by the distribution of stations and seismic events.The main works involved in this dissertation includes: 1) on the basis of the existing research, we calculate the synthetic seismograms of the receiving functions of the stratified-crustal anisotropic media with back azimuths by using the generalized reflection-transmission coefficient matrix method, and study the effects of the anisotropic parameters at different layers on the receive function wavefield; 2) introducing the curvelet transform theory into the receiver function study and combiningthe compressed sensing theory with the curvelet-based denoising method,we realize denoise of the receiver function and wavefield reconstruction of missing data, simultaneously; 3) using the particle swarm optimization theory, we develop a global inversion algorithm of stratified anisotropic receiver function; 4) the proposed method is applied for the interpretation of the Sichuan movable array data.Our results show that 1) when anisotropy parameters of double layers are the same, the wavefield of their receiver function is almost same with that of a single layer, and the wavefield of their receiver function are greatly affected not only by the anisotropic parameters of each layer,but also by the differences of anisotropic parameters between the layers;2) the anisotropy of the receiving function is sensitive to the azimuth angle of the anisotropic symmetric axis more than its plunge; 3) the tangential component of the receiver function is sensitive to the anisotropic parameters more than its radial component; 4) different from the isotropic thin layer, the anisotropic thin layer can lead to discrete conversion phase; 5) the anisotropic thin layer between layers make only limited effects on the receiver function wavefield, but the reverberations within the sediments will disturb the estimation of anisotropic parameters of the crust; 6) the tests from the observed data and the numerical tests show that the scattering noise in the receiver function caused by the complex crustal media and its laterally inhomogeneous structures can be effectively suppressed via the curvelet-based denoising method, and the receiver functions at missing orientations can be well reconstructed; our method can be used not only for processing the data recorded at a single station, but also for array observation of a single event; however, the former case is better than the latter; 7) the numerical test and validation results show that in case of the fixed isotropic velocity model, the anisotropic parameters of the stratified crust can be reliably obtained from the receiver function via our global inversion method based on the particle swarm optimization;8) introducing the denoise technology is of great valuable to correctly parse anisotropic parameters of different layers; 9) the results from the receiver function data of the West Sichuan array show that, the anisotropy of the crust beneath the eastern Tibet is layered, and the differences of the anisotropy in different layers suggest that the crustal deformation at different strata is in different styles.In short, the results of this paper provide a new theoretical basis for the study of the stratified crustal anisotropy from the receiving function. However, in view of the complexity of the crustal structure in the eastern Tibet Plateau, its layered anisotropy is still needed to be further studied.