Using Receiver Function Method To Study Crustal Structure In Nanling Area

The South China block is located in the south of the Jiangnan orogenic belt and the southeastern margin of the South China Craton.It is also the first site where the three major plates interact with each other: the Eurasian plate,the Philippine Sea plate and the Western Pacific plate.The South China block is not only distributed with many faulted structural belts,but also has polymetallic metallogenic belts such as the middle and lower reaches of the Yangtze River,Wuyi,and Nanling.In order to study the characteristics of the crust-mantle structure of the South China block,this study deployed a line across the Dayu-Xingguo fault zone,Shaowu-Heyuan fault zone,Zhenghe-Dapu fault zone and Changle-Nan'ao fault zone from July 2017 to August 2020.Broadband seismic survey line of the fault zone.The survey line is composed of 80 mobile broadband seismographs,the stations are 5-8 kilometers apart,and the total length is 430 kilometers.A total of 410 teleseismic event waveforms with an epicentral distance of 30°-90° and a magnitude of more than 5.5 were intercepted from the continuous seismic waveforms collected by the station,and then 894 teleseismic P-wave receiver functions were extracted.In this paper,the H-? scanning stacking method in the receiver function method is used to obtain the crustal thickness,wave velocity ratio,Poisson's ratio and other information under the survey line in the study area.The main results are as follows:(1)The thinnest part of the crust under the survey line in the study area is 23.9 km,the thickest part is 35.1 km,the average thickness is 29.67 km,and the overall thickness is relatively thin.The trend of crustal thickness change from west to east is bounded by three fault zones,which first become thick from thin and then from thick to thin.The reason may be that the three fault zones through which the survey line traverses are approximately parallel,and magmatic activities of continental rift system have occurred in history,thus developing the topographic characteristics of both sides uplift and middle sag.(2)The crustal wave velocity ratio under the survey line in the study area shall be at least1.60,at maximum 1.95 and at average 1.75.The variation of the ratio of wave velocity is not uniform,and the value of the ratio of wave velocity in the fault zone is larger,maybe because the fault zone provides a passage for magma intrusion.(3)The Poisson's ratio under the study area is 1.58,1.90,and 1.76.The trend from inland to coastal is higher and higher,which may be caused by the crustal evolution in South China since the Mesozoic.The Poisson's ratio decreases with the increase of crustal thickness,which may be caused by the thrusting nappe structure and extensive folds in the study area.