Structure Of Crustal And Upper Mantle’s Discontinuities Beneath NE China-Revealed By Receiver Function

The Northeast China(NE China)sites between Siberian Plate and North China Plate,and the Pacific Ocean to the east.Since Paleozoic,The NE China has sequentially been influenced by multiple tectonic activities,such as the close of Paleo-Asian Ocean and Mongolia-Okhotsk Ocean,those tectonic activities had a huge influence on the deep structure beneath NE China.So the research on crustal and upper mantle’s discontinuities is significant for deducing the tectonic origin in NE China.Recently,the receiver function method has been widely applied to investigate the structures of the crust and upper mantle.In this work,we study the high-resolution crustal structure of Northeast China by using receiver function method.A total of 259 stations which consist of the China Earthquake Administration,NECESSArray stations and 26 Ji Lin university temporary stations are used in this study,and finally selected 16,070 high-quality receiver functions.We use the H-κ and CCP stacking methods to obtain a high-resolution crustal structure beneath Northeast China.The results show that the Moho depth beneath study area generally coincide a mirror relationship with the surface elevation.The west portion of Great Xing’an Range exist an abrupt change for Moho depth.In the center of study area,the crustal thickness of Songliao basin is very thin due to the regional extension in late Mesozoic.In Songliao basin,the variation of Moho is decreasing from the west to east,and we speculate it is related to the subducting Pacific slab.The east part of the study area really has a complicated Moho structure,and multiple phases can be observed between Yilan-Yitong and Dunhua-Mishan faults,which may relate to the mantle-material’s underplating.Around Changbai volcano area,a thick crust and high Vp/Vs structure can be observed,which indicates that magma chamber maybe exist in the crust.Our results provide an efficient geophysical constraint on the crustal structure and dynamic in NE China.The H-κ stacking method is effectively to estimate the crustal parameters beneath the station used the receiver functions from the stations lying on the bedrock,however,for the stations locating on sedimentary basin,the low-velocity sedimentary layer can give rise to strong reverberations in receiver functions,usually influencing and even masking the useful phases from Moho discontinuity,then obtaining an incorrect estimating of crustal structure.In order to accurately measure the crustal structure in the sedimentary basin,we present a method that using the predictive deconvolution method to remove the near-surface reverberations,and autocorrelation is also applied on the observed receiver functions to determine the prediction step length,which is defined by the two-way travel-time of the S wave in the sedimentary layer.Synthetic and actual receiver function tests show that,the near-surface reverberations can be effectively removed by applying predictive deconvolution method,and the processed receiver functions are suitable to accurately estimate the subsediment crustal structure using an improved H-κ stacking method.Contrast to the other methods of removing near-surface reverberations in receiver function,the proposed method has the features of simple parameters,small computational complexity and clear phases,which is suitable to mass data processing.The evolution of Changbai volcano is an important tectonic issue in NE China.We study the detailed mantle transition zone(MTZ)structure beneath the active Changbai intraplate volcano using a receiver-function method.A total of 3005 teleseismic receiver functions recorded by 26 Jinlin University(JLU)and 44 China Earthquake Administration(CEA)broadband stations are obtained by using a common-conversion-point(CCP)stacking method.For conducting the time-to-depth conversion,in addition to the one-dimension(1-D)IASP91 model,we also use a three-dimension(3-D)velocity model of the study region so as to take into account the influence of structural heterogeneities.The 3-D conversion points of Ps waves are distributed in an area with 122°E~132°E longitude and 38°N~48°N latitude,and in a depth range of 350~750 km.Our results reveal significant depth variations of the 410,520 and 660 km discontinuities.A broad depression of the 410 km discontinuity and a low-velocity anomaly are revealed beneath the Changbai volcano,which may reflect a large-scale partial melting around the 410 km discontinuity with a positive Clapeyron slope.The 520 km discontinuity is identified clearly and its uplift occurs above the stagnant Pacific slab.We also find a prominent depression of the 660 km discontinuity,which is elongated along the trend of deep-earthquake clusters in a range of 39°N~44°N latitude,and the depression area has a lateral extent of about 400 km.Because the 520 and 660 km discontinuities correspond to positive and negative Clapeyron slopes,respectively,we think that the 520 uplift and the 660 depression are caused by the cold subducting Pacific slab.A part of the Pacific slab may have penetrated into the lower mantle and so caused the large-scale 660 depression in front of the deep-earthquake clusters.Our results also reveal a part of the upper boundary of the subducting Pacific slab in the MTZ.These findings shew new light on the complex structure and subduction dynamics beneath the Changbai intraplate volcano.