Pn Velocity And Anisotropy Of Uppermost Mantle Beneath East China And Adjacent Regions

East China is consist of Northeast China (eastern part of the Central Asian orogenic belt), North China Craton, Sulu orogenic belt and the South China block,which is located in the southeastern portion of the Eurasian plate, and closed to the west of Pacific subduction zone. With the influence of the westward subduction of the Pacific plate, this area has the complex geological structure and deep structural characteristics. To study the structure of uppermost mantle beneath this area will help us understand the influence of the deep structure on the shallow structure during the continental dynamic evolution.Early studies mainly used Pn arrival time from seismic reports (such as the Annual Bulletin of Chinese Earthquake and the reports of local seismic networks).The recent study supplements the Pn data recorded by the portable stations in Tibet Plateauin and focus on the study of velocity and anisotropy of uppermost mantle beneath West China.In this study, we use the data from the bulletins of ISC (the International Seismological Center), the Annual Bulletin of Chinese Earthquake and the reports of local seismic networks. We also cut earthquake events recorded by Northeast China North China temporal stations, and regional permanent seismic stations in east China. We manually picked up a large number of high-precision Pn arrival times from these events. Finally, we use 240814 Pn arrival time from 24072 earthquakes recorded by 2049 stations, which has made Pn rays densely cover the East China. We determined the Pn velocity and anisotropy of uppermost mantle beneah East China and adjacent regions by using Pn anisotropic tomographic method.The results show that the average Pn velocity of uppermost mantle in East China is 8.06 km/s and the variation range is 7.81-8.32 km/s. The eastern portion of Northeast China is characterized by low velocity anomalies, which may be affected by the Pacific subduction plate and represent the upwelling of hot materials from Changbaishan volcano. The east and centre of North China Craton (NCC) exhibit low velocity and the west NCC shows high velocity, this results may imply that the Ordos block in the west is a stable block, while the east and centre area may have experienced destruction and modification. The stable South China block is mainly characterized by high velocity anomalies. The results also show that the small Basin like Jianghan, Xialiaohe, Erlian and Hailar basins all exhibit high velocity, while large Sichuan basin and Songliao Basin show a heterogeneous structure characteristics.The high velocity anomalies in the Sichuan basin show obvious partitioned phenomenon,which may be caused by different base materials before depositing. The Songliao Basin exhibits high velocity in the north and low velocity in the south, which may imply that the lithosphere of the southern part of the basin has been modified. This study further reveals that Pn anisotropy is related to the distribution of velocity structure. The Pn anisotropy is strong in low velocity region and high-low velocity transition zone, and most strong earthquakes occur in the crust above these regions. It may indicate that these parts are prone to deform and stress concentration or engender stress difference. The Pn anisotropy near some basins is relatively strong, which may reflect the extensional tectonic setting during the basin evolution.