The Structure Of The Crust And Upper Mantle In Northeast China From Teleseismic Receiver Function

Northeastern China is located east of Xingmeng orogen, north of the North China Craton, west of Pacific Sea. As a back-arc region of subduction of the Pacific, not only deep earthquakes frequently occered, but also one of the most intense areas of volcanism, is the ideal place to study the dynamics of the Pacific subduction.Firstly, we introduced the results of the crust and upper mantle structure study and northwest Pacific subduction in the recent years in the northeastern China. We compare the receiver function results with the tomography, triplicate waveform and do the further study about crust anositropy and crust and upper mantle structure by receiver functions.We use teleseismic data recorded by116temporary stations and121national earthquake network stations located in NE China to calculate the receiver functions and got the crust anositropy by auto mative shear-wave splitting program, and also get information of crustal thickness and Poisson's ratio by H-K stacking. We also use CCP stacking method to map the topography of the upper mantle discontinuities and do some preliminary investigation with the deep dynamic model of northeastern China.Results are summarized in the fllowing.l)The delay time between fast wave and slow wave of the crust anositropy in the northeastern China is about0.15-0.3%秒. It is much smaller than the time delay of SKS/SKKS anositropy. The crust beneath most stations show the fast wave polarization direction is nearly northwest, the same direction as the tensile stress and the movement of the plate. We infer that the main stress of the crust is tensile stress. But also a few stations located near the fault and Greater Khingan Mountains show a different fast wave direction which is northeast. This mean the crustal anositropy is regional and complexity. By the compareation with SKS/SKKS in the same area, the crustal fast wave polarization is almost the same as it of the SKS/SKKS. And this means the anositropy is come from the under crust, and this reflect that the consistency of the crust and mantle vertical deformation.2) The overral performance of the crustal thickness of the northeastern China is eastern and western thicker than the central. The crustal thickness beneath Greater Khingan Mountains, Hulunberer Plateau and Jiamusi massif are much chicker, about36-42km. In the Songliao Basin, Lesser Khingan Range trough fold belt, Jiaoliao uplift, east of Yanshan bold belt and south Liaohe Basin the crustal thickness is thin, and it is between29km and36km. The Poisson Ratio in the study area is a little higher, such as it in the Greater Khingan mountains bold belt, Songliao Basin, Changbai mountains the Poisson Ratio is larger than0.25. the high value of Poisson Ratio means that beneath this region maybe exist melting(Changbai Mountain) or upwelling make the under crust contains much Fe and Mg elements. The heat flow in this region is always higher than around. The Moho is flat in the west of the gravity lineament. With the influence of the deep faults which named Nenjiang faults, Yilan-Yitong faults and Dunhua-Mishan faults, the Moho becomes up and down in some region. Especially near the Dunhua-Mishan faults, the Moho shows a clear dislocation, we infer it has a close relationship with the Pacific slab subduction.3) Both the410km and660km discontinuities express a wide range of sinking. The410km discontinuity about sinks10km and the660km sinks10-30km. We infer there exists upwellings beneath the Songliao Basin from the thickness of the upper mantle transition zone become thinner. There are several interfaces near the660km in Yilan-Yitong faults, it is suggested that the subduction slab reached near this location and making the mantle materials upwelling and make a seriously influence on the Songliao Basin.