Studies Of Receiver Functions Analysis And The Crustal And Upper Mantle Structures From Broadband Seismics

Though plate tectonics in geology can well explain the kinemics and dynamics of oceanic plates, it is a challenge to explain the intra-continental deformation by plate tectonics, since compositions and rheological structures of continental lithosphere are different from those of oceanic lithosphere. Another important issue of plate tectonics is about the refine structures of the continental lithosphere. The details of the crustal and upper mantle structures are very important to study the continental lithosphere and the continental dynamics. Thus, the challenge to plate tectonics is a great chance to Seismology, which is the most effective way in investigating the inner earth. With several decades of improvement, the seismological method-receiver functions, which investigate the inner structures of earth by converted waves, have become a common and effective way in the study of refine structures beneath seismic stations.The continent in China formed by the convergence of several blocks, which was affected by several intensive tectonic events. At present, it is in the domain of the Indo-Tibet collision and the subduction of west pacific, and suffered significant intra-continental deformation. Beneath related regions with intensive tectonics, the crustal and upper mantle structures are very complicate. Thus, it requires improving the investigation and data analysis, to provide accurate evidence to study the intra-continental dynamics. Based on the study of receiver functions, we proposed following improvements. Updip H-k stacking could reduce the influence of dipping Moho in calculating the average crustal thickness and Vp/Vs ratio, polarization analysis are applied to enhance the signal to noise ratio and accuracy of data cutting, and lateral sliding window is introduced to CCP stacking method to increase the rays coverage and lateral resolution. By applying these improvements to following interesting study regions, we obtained refined crustal and upper mantle structures for the study of intra-continental dynamics.In southwest Yunnan, the crustal structures are very complex for the influence of Indo-Tibet collision. We applied the updip H-k stacking method in this region and obtained reliable result of the variation of Moho depth and average crustal Vp/Vs ratio. This evidence is important for southeastward flowing of the lower crustal materials beneath Tibet Plateau.From the Paleozoic to the Mesozoic, Weihe Graben and adjacent regions experienced three impressive compressional tectonic events, and the tectonic regime transformed to extension in the Cenozoic as the far-field effect of India-Tibet collision. The receiver functions study reveals that the thick sedimentary in the graben failed the P wave receiver functions, while the S wave receiver functions are not affected. Thus, the CCP stacking image of the S receiver functions represent reliable evidence for the crustal structures. The CCP image shows impressive lateral variation of Moho depth, which varies from-20km to-50km. The Moho dips towards the south beneath every tectonic unit, and presents significant discontinuity, such as uplift, offset and overlapping, between these tectonic units. The crustal structures suggest that the compressional tectonic events before the Cenozoic were very intensive and resulted in the large scale over-thrusting zone in the lower crust and the most upper mantle. The far-field effect of India-Tibet collision in the Cenozoic has limited effects on the deep structures. The crustal structures indicate that, the crustal extension was limited in Weihe graben, and barely affected the Moho below and the crustal structures beside Weihe Graben.As the oldest tectonic unit on the earth, craton is very important to study the construction of continent and the tectonics in the Archean. North China Carton (NCC), the most important tectonic unit in China, formed in the Paleoproterozoic and its east block suffered destruction in the Mesozoic. In the southern NCC, our receiver function analysis shows that thick cratonic lithosphere remains and the depth of LAB is～380km. The west part of the NCC is very stable with a thickness about280km, and it contains a partial melting belt at～120-200km, which is probably the common character of stable cratons. The Mesozoic cratonic destruction limitedly affected the cratonic lithosphere beneath the trans-NCC Orogen and the east part of the NCC. The lithosphere at the～80-200km depth is partial melted which results from the Mesozoic cratonic destruction. Beneath this partial melting zone, there is the remains of Archean lithosphere, which reaches the depth at～380km. There are inner structures in the remains of Archean lithosphere. A high-velocity slab extends from the most-upper mantle of the western NCC into the remains of Archean lithosphere. This slab were explained as the Paleoproterozoic subducted slab between the east and the west parts of the NCC, which indicates the subduction was eastward with low dipping angle. This study provides evidence for the construction, evolution and destruction of craton.By improving the applications of receive functions, we obtained the refined crustal and upper mantle structures beneath the regions suffering intensive intra-continental deformation, analyzed the related dynamics and mechanism, and provide the details of deep structures for the study of intra-continental deformation.