The Study Of Receiver Function Method And Lithospheric Structure Beneath The Northern Of North China Craton

With the quick development of the seismic networks and the portable broadband seismic observation technique, the teleseismic receiver function (RF) method has become the most important method of exploring the crust and upper mantle structure since the receiver function was proposed by Langston. However, the lithospheric thickness estimated by PRF suffers from interference from PsPs+PpSs phases, and no areal LAB distribution was revealed within the limitations of the dataset.Farra and Vinnik proposed the S receiver function (SRF) using the similar method of RF. Due to the S to P (Sp) conversions phase from deep velocity discontinuities arrived before the direct S phase, the S receiver function (SRF) technique appears to overcome this problem and can be used to identify the lithosphere-asthenosphere boundary (LAB). However, the researches about the synthetics of SRF are still very less and there are also some disadvantage about the SRF, so we did some research about the synthetics of SRF to achieve the process of the SRF calculation and some special considerations.We calculated the systhetic seismogram and the synthetic RF by using the FK method and iterative deconvolution method. We obtained the best range of the epicentral distances and the time window for deconvolution. After calculating the incidence angle of Sp wave, we consider it is necessary to roate the seismogram before deconvolution.Since the seismic migration imaging method was applied to image the seismic array data, the RF stacking image method was widely used to image the crustal and upper mantle structure. However, there is some inherent defect due to the plane wave approximation. We improved the common conversion point (CCP) stacking method by calculating the relation between the rayparameter and the converted depth. The improved CCP stacking method can project the convert wave amplitude to the position near the real convertion position.We calculated the SRFs and determined the crustal and lithospheric structure in North China Craton (NCC) by using teleseismic waveform data collected by two seismic arrays in the NCC. The Moho depth decreases from40km beneath the western NCC to30km beneath the eastern NCC. This observation is quite consistent with that from PRFs, although the resolution of SRFs is lower than that of PRFs due to the longer periods of S waves. The LAB depth varies from60km to80km beneath the central and eastern NCC with no abrupt change and the lithospheric thickness decreases from130km to80km in the western NCC. Two negative interfaces were revealed in the NCC, we consider the shallow one is the MLD and the deeper one is LAB and the LAB overlapped with the MLD in the central and eastern NCC. The surface wave tomography results and the SKS splitting results support our results.We calculated the PRFs and determined the fine crustal structure in Cangdong faults by using teleseismic waveform data collected by a seismic array in Bohai Bay. The results revealed that the basement depth varies strongly in Cangdong faults and our result is consistent with the results obtained by the deep seismic sounding profiles and tomography.Combined with the results of seismic tomography, SKS splitting studies and the thermal studies, we discussed the thining mechanism of the NCC. We consider that the thinning of NCC is the result of mantle flow beneath the margin of Ordos plateau and the mantle flow caused by the subduction of the Pacific plate. The mantle flow caused by the subduction of the Pacific plate is responsible for the thinning of the eastern NCC. The subduction of India plate caused the upper mantle material of the Tibet plateau flows to the east and become a bifurcated flow around the Ordos plateau. We suggest that the horizontal mantle flow beneath the northwestern margin of Ordos plateau and the mantle flow generated by the subduction of the Pacific plate converge beneath the Shanxi rift and cause the thinning of the lithosphere beneath the central NCC and the eastern part of the western NCC. Our results provide an important source of information for understanding reactivation and destruction mechanism of the NCC.