Receiver Function Inversion And Research Of Crustal Structure Beneath KMI Seismic Station

Receiver function has been proved to be very useful for the determination ofcrustal and upper mantle discontinuities. In this thesis receiver function is particularlyanalysed. A new technique is tried to improve time series filter of the seismic records.This method is utilized to obtain the crustal structure beneath the KMI digital seismicstation in Yunnan province and works quite well. Details about receiver function areexplored as follows:1. The concept of P-to-S converted wave of teleseismic and the three-componentrecord is explained.2. Forward problem: The method of generalized reflection-transmission coefficientmatrix is used to compute three-component seismograms. Transverse componentin theoretic seismograms is zero in isotropic media. Source equalization theory ofreceiver function is deeply discussed. The meanings of the water level fractionand Gaussian filter-width parameter are described.3. Backward problem: The least-square method is introduced to do inversion andpeeling algorithm of inversion which suggest doing inversion step by step fromshallow crust to deep crust is improved. This technique can remove the effects ofthe multiples in the internal crust and conversions at the base of the sediments onMoho conversions to get real velocity structure of S wave by horizontalcomponent inversion.4. The free crustal structure is obtained beneath KMI digital seismic station withreceiver function analysis. Moho depth is about 45km in northern crust and 42kmin southern crust and 43km in average. Its whole crust can be described asthree-layer structure. The average thickness of the thick upper crust is about 15km,and the average velocity is 3.48km/s. The middle crust is about 15-27km, and itsaverage velocity is 3.8km/s. The northern lower crust is about 27-45km, and thesouthern lower crust is about 27-41km. The average velocity is 4.05km/s. Theheterogeneity has been found between the northern and southern crust beneath theKMI digital seismic station. In upper crust there is an obviously lower-velocityzone in northern crust than that in southern. Its configuration bound is basically ingood agreement with the sediments cover. A low-velocity zone(3.3km/s) deepfrom 2km to 4kin is found in southern crust, which is corresponding with thedrape section. In southern crust the velocity is low from about 10km to 20km, andthen increase from about 40km to 50km because of the influence of the southernmantle, and the high-velocity zone move northward with depth increasing.These important geophysical parameters are correlated with the structure of Yunancollision zone. They may provide some evidence to the procedure of geodynamicsand mechanism of structure deformation of Yunnan block.