Seismic Lg Wave Attenuation Measurement Method And Its Application In Northeast China And Yunnan

Northeast China and its adjacent areas are the intersection of the West Pacific tectonic belt,the North American continental plate and the Central Asia orogenic belt,China Korea,Yangtze plate,etc.Under the macro background of Pan continental amalgamation and breakup,they have experienced many tectonic events since the Meso Cenozoic.In the late Mesozoic,with the closing of the paleo ocean and the collision of plates,a complete northeast road block was formed,which was affected by the subduction of the Pacific plate in the Cenozoic.Using the waveform data recorded by 380 broadband seismographs,the Q₀ value of Lg wave in Northeast China and its adjacent areas is studied.The effect of instrument response,source function and site effect can be effectively removed by using the anti double station method,and more accurate Q value can be obtained.By using the Q₀-value of 19862 anti bistatic paths,we obtain the high-resolution image of the Q₀-value of Lg wave in this area.The Q₀-value distribution of Lg wave has a good correspondence with the surface structure and Cenozoic structure in this area.Most of the Cenozoic volcanoes are located in the area where Q₀ value changes greatly.In the sedimentary basin and North China Craton,it shows low Q₀ value and high attenuation,which may be that the crust in these areas has not been affected by the Cenozoic tectonic movement.The calculation of Lg wave Q in northeast China not only provides constraints for the study of crustal structure in this region,but also provides basic data for the monitoring of nuclear tests.A large number of nuclear testing sites are scattered around China.In recent years,underground nuclear testing has become more anti-reconnaissance and covert.The China seismic Network can be used for regional seismic monitoring of nuclear tests taking place near the test site.The monitoring and analysis of nuclear tests should be carried out in the interests of national security and the fulfilment of international social responsibilities.Seismological method has become an important means of monitoring underground nuclear test.It is of great significance to fully study the data from North Korea's underground nuclear test and develop the method of analyzing nuclear test parameters based on regional seismic data in the surrounding areas of China.Based on 94 stations of China Seismological Network in Northeast China,combined with the accurate Q value of Lg wave in the path from event to station,the magnitude of Lg wave in North Korea's last five nuclear tests is calculated.The magnitude results can provide data for the subsequent equivalent calculation.The Qinghai-Tibet Plateau is generated by the collision of the Indian plate and the Eurasian plate,which is accompanied by complex tectonic movement and deep dynamic process.In the past,the interpretation of the lateral extrusion model of Qinghai-Tibet Plateau was mainly divided into rigid block extrusion model and crustal flow model.The southeastern margin of the Qinghai-Tibet Plateau,which is located in Yunnan province,is considered as the site of crustal material transfer in the Qinghai-Tibet Plateau in both models.In this paper,470 broadband seismic records of natural earthquakes with M?4.0 between May 2014 and May 2019 recorded by 121 fixed stations in and around Yunnan Province are collected.6976 high-quality vertical wave data are processed by using the inverse two station method.The attenuation imaging of Lg wave at 1Hz with spatial resolution less than 100km in Yunnan area is inverted.The study of crustal attenuation in Yunnan by Lg wave is helpful to understand the tectonic evolution and crustal dynamics of Qinghai-Tibet Plateau.