Research On Joint Seismological Inversion Methods For The 1-D Layered Crustal Structure

The study of crustal structure is of great significance for understanding the physical properties of the seismic source,the mechanism of crustal deformation,and the dynamics of the crust and mantle.In recent decades,seismologists have developed many joint inversion methods to obtain the fine velocity structure of the crust.However,the existing joint inversion methods used to study crustal structure focus on the shear wave velocity structure,there is less research on the joint inversion of layered VP/VS ratio and azimuthal anisotropy.Considering the importance of the VP/VS ratio and the anisotropy for our understanding of the internal structure and deformation of the earth and the insufficiency of related research methods,this paper studies joint seismological inversion methods for the 1-D layered crustal structure.The research mainly includes the following two aspects:(1)A method for inverting 1-D layered crustal VP/VS structure by combining Rayleigh wave dispersion,ZH ratio,and receiver function data.The receiver function has strong constraints on the average VP/VS of the crust,on the other hand the surface wave data(phase velocity and ZH amplitude ratio)are sensitive to both the S-wave velocity structure and the P-wave velocity structure.The existing two-step inversion scheme of these three kinds of data can obtain a more reliable one-dimensional shear wave velocity structure.On this basis,this thesis proposes a new method of inverting the crustal shear wave velocity structure and the VP/VS structure simultaneously,which was used as the third step to invert the reliable layered VP/VS structure within the crust.We conducted a series of synthetic data tests on the method to verify the reliability of the method,and then successfully applied it to the real data recorded by a permanent station located in the Sichuan Basin.The inversion results of this station indicate the existence of a 10-km thick high VP/VS layer in the shallow crust beneath the station,which corresponds to the very thick sedimentary layer in the Sichuan Basin.However,the middle and lower crust has a medium-low VP/Vs ratio,corresponding to the ancient crust of this location.(2)A method for inverting 1-D layered crustal azimuthal anisotropy structure by combining Rayleigh wave dispersion and ZH ratio.The azimuthal anisotropy of the crustal medium provides important constraints for studying the evolution and deformation of the earth.Traditional methods usually use shear wave splitting,surface wave dispersion inversion,and other methods to study the crustal azimuthal anisotropy of S-wave velocity.However,different methods and data often give different results.Therefore,we have developed a method that combines Rayleigh wave dispersion and ZH ratio data to invert 1-D layered azimuthal anisotropy.Make full use of the consistent and complementary sensitivity of Rayleigh wave phase velocity and ZH amplitude ratio.Synthetic data test shows that our method has strong anti-noise ability,which can obtain stable and reliable results even with noisy data.The two seismological joint inversion methods of the crustal structures proposed in this thesis can obtain a more reliable layered crustal VP/VS ratio structure and azimuthally anisotropic S-wave velocity structure beneath the station,providing important tools to study the crustal structure and deformation characteristics.