Constraining Moho Characteristics With Frequency-Dependence Of Receiver Function And Its Application In Northeastern Margin Of The Tibet Plateau

The complexity of the Moho,although reflected in many observations of seismology currently,is rarely discussed.Actually,the study of the properties of the Moho is of great significance in the scientific issues of crustal material composition,crust-mantle material exchange,the internal temperature and pressure environment of the earth and interaction between blocks.Nowadays,the accumulation of massive observation data provides us with the possibility to try studying the complexity of the Moho.In this study,based on the simulation of full-waveform theoretical seismograms of different Moho velocity models,the receiver functions at different frequencies are calculated.Through systematic analysis of the frequency-dependence characteristics of the theoretical receiver functions of different Moho velocity models,it is found that the properties of the Moho are reflected in the frequency-dependence characteristics of the receiver functions to some extent.According to the results of numerical experiments,receiver functions at different frequencies based on different Moho velocity models are classified and summarized,which can be used as important reference for studying the frequency-dependence characteristics of Moho in observations.Take,for example,Gaotai Seismic Station,fixed station located on the northeastern margin of the Tibet Plateau.Based on 5 years' teleseismic records,the receiver functions at different frequencies are deeply analyzed.The morphology of the Moho beneath the station was analyzed with reference to the numerical test results,and the crustal and Moho velocity models beneath the station were constructed.The results show that the Moho beneath the Gaotai Seismic Station is not a simple first-order velocity discontinuity,but a velocity transition zone.Combined with previous research results of artificial earthquakes and petrology in this area,the properties of the Moho beneath Gaotai Seismic Station was analyzed and discussed.Further,we applied this analysis method to a high-density temporary seismic array on the northeastern margin of the Tibet Plateau.Based on 2 years' teleseismic records and according to the distribution of piercing points,the frequency-dependence characteristics of stacking PMs phases on different profiles are analyzed.The results show that the short-period receiver function splitting characteristics in research area are variable,and there are obviously different splitting characteristics on both sides of the majority faults.Meanwhile,the different splitting characteristics appear alternately along the profile's direction in the area.It is likely that the uplift of the Tibet Plateau and its expansion to the northeast led to the complexity of the crustal structure in the area.Receiver function method is a widely used seismological method for studying crustal structures.But in most researches with receiver function,Moho is generally assumed as a sharp first-order velocity discontinuity,and its properties are less discussed.As the seismic observation data massively increases,we can relatively accurately extract the information caused by the complexity of the Moho.Based on the numerical test results and the summary and analysis of the data of single fixed station and mobile observation array,this study demonstrates the feasibility of studying the complexity of the Moho and provides a feasible idea for the study of the properties of the Moho.