Study Of The Crust-mantle Discontinuity Structure In Eastern China With Receiver Function Method

For the crust-mantle discontinuity structures in eastern China.,the following work has been done:Based on the traditional H-?stacking method of receiver function,we propose an improved iterative H-?stacking method.The method needs two steps of stacks.The first step we use the converted wave at the bottom of the sediment to get the thickness and Vp/Vs ratio of the sediment.The second step we use the results of the sediment and the converted wave at Moho discontinuity to calculate the crustal thickness and Vp/Vs ratio.The Taylor series expansion and "recovery test" show that the error of this method is very small(<0.8%).From the actual data test,it can be seen that when there is a certain thickness of sediment layer under the station,the thickness of sediment and crust obtained by the improved sequential H-?stacking method is similar to that obtained by Deep Seismic Sounding,while the result obtained by H-?stacking method has a large error and can not be used.We have studied the large sedimentary basins in eastern China by using the improved sequential H-?stacking method,and obtained the sedimentary and crustal thickness of Songliao basin in northeastern China,Ordos basin and Bohai Bay basin in northern China,and Sichuan basin in southern China.If the stations are densely distributed enough,the improved sequential H-?stacking method can clearly delineate the morphology of sedimentary basins and secondary tectonic units of the basin,and correspond well with known geological units.Using 187 teleseismic event waveforms recorded by temporary and permanent stations in the northeast part of North China Craton,we obtained the crustal thickness and the average Poisson's ratio of the crust in this area.We find that there are obvious structural differences between the east and west sides of the North-South Gravity Line.The crust on the west side of the North-South Gravity Line is thicker,the average Poisson's ratio is lower,while the crust on the east side is thinner,and the average Poisson's ratio is higher.The structural characteristics of the results and data fitting both indicate that The western part of the North China Craton,which is located on the west side of the gravity gradient zone,may still be relatively stable,while the eastern crust is intruded by the thermal material of the underlying mantle during the process of extension andthinning,which greatly increases the mafic components in the crust.The highly evolved crust indicates that the eastern part of North China Craton is likely to have experienced delamination.The above crustal characteristics shows that the eastern part of the North China Craton Crustal has undergone more severe destruction than the western part.Using 762 teleseismic events recorded by permanent stations in South China,we obtained the structure of 410 discontinuity,660 discontinuity and mantle transition zone of South China using both the one-dimensional Iasp91 model and tomography three-dimensional model.In the eastern part of South China,the mantle transition zone has not experienced large-scale thickening,which indicates that the westward subduction of the Pacific plate has not stagnated beneath the East Yangtze Craton.In the western part of the study area,we found that the local thickening may be caused by the detachment of the Yangtze Craton lithosphere.There are two hot spots in South China.One is Tengchong volcano on the West side.It may originate above the mantle transition zone with a depth of less than 410 km.The eastward subduction of the Indian plate fractured beneath Tengchong volcano,which triggered an upwelling of thermal material to form Tengchong volcano.The second is the Hainan mantle plume,whose hot spot originated below the mantle transition zone and its depth was more than 660 km.The thermal material of Hainan mantle plume upwells in an inclined state.