The P-receiver Function And Velocity Structure Tomography Of Upper Crust In Jiangsu And Anhui Province

The surface and interior of the earth has been in a constant movement since its formation.Surface morphology of the Earth is mainly caused by the combined action of the earth’s internal and external forces, and the internal is often considered to be an important reason for the difference in the surface topography. ’The theory of Plate Tectonics’ in the today’s pattern of land and sea, plate motion, large scale tectonic features is a more plausible explanation,and theory expounded Rigid and flexible lithosphere beneath the plastic asthenosphere, and Mutual movement between the plates is due to the asthenosphere convection caused.There is a relationship of mutual compensation between Subduction and dilatation of plates that the expansion of the plate along the separated boundary can cancelling out the demise of plate along with the convergent boundary in global scale,so the radius of the Earth remains stable. Moho surface,as the crust-mantle interface, both Is strongly influenced by the asthenosphere, and affects the movement and evolution of the Earth’s crust, therefore It is necessary to discuss internal dynamics of the Earth By understanding the depth, velocity ratio and Poisson’s ratio.On this basis,we study Pg velocity anomaly distribution of upper crustal by 2-D Tomography,and explore the geological structure of the contact surface and deep.Ultimately, we can conduct a comprehensive analysis of the study area.In this paper, the study area for the Jiangsu and Anhui provinces,where is located in eastern China.this area is not only long-term affected by the Pacific Plate, Indian Plate, Philippine Plate by from the external environment,but is the North China Block, the Yangtze block, Dabie orogenic belt convergence zone. There is Underground development of a number of faults.Taking into account the above factors, Geological structure features of this area is complex and diverse.In addition, this place is a long-term concern due to frequent earthquakes.So It has important significance and value to study seismic velocity and geological structure.We hope that through this research to obtain relevant and useful information, and provide important reference information to geological structure and earthquake disaster prevention. This work can be divided into two aspects of the content of the following:Basis on consecutive three years datas from 2012 to 2014 recorded by broadband seismometers of stations in Anhui and Jiangsu provinces,we finished studying Moho deepth and Velocity ratio,Then calculating Poisson’s ratio of underground beneath stations.From the results of the study point of view,Moho depth in Jiangsu and Anhui provinces is generally 32-38 km except of a few of area that moho deepth is nearly 40 km, and Coastal areas crustal thickness thin to less 30 km.The Moho depth of Tan-Lu fault zone south section of both sides showed significant difference.We found that the velocity ratio varies greatly from 1.6 to 1.8,and Poisson’s ratio in the range between 0.19 and 0.29.Combine with Geodynamics and geological characteristics,we thought Yangtze plate,as an active plate, continued to squeeze inside the North China Plate, so that Plate beneath the North China is still in the background of a strong stress.Moreover our result about moho deepth is consistent with fact of gradual disappearance of the Sulu orogenic belt root, it is a reasonable explanation that asthenosphere mushroom cloud is fromed by upwelling asthenosphere substance.In addition, we finished 2D seismic tomography inversion with travel times of 4922 Pg waves that recorded by 56 stations in Anhui,Jiangsu,Henan and Zhejiang from 1976 to 2014. From the results, the Pg velocity in the southern area of North China is about 6.5Km/s and its lateral velocity variation is between-0.44Km/s and +0.48Km/s.The velocity distribution in the study area has a good corresponding relationship with the surface topography, and the characteristic of velocity distribution reflects the mutual coupling between North China Block, the Yangtze Block and the Dabie orogenic belt. The results confirm that high speed body on a large scale under the HP or UHP metamor Phiebelts is nonexistent in Dabie Mountains.Furthermore, the high-frequent earthquake area, for instance, Huoshan seismic window, is located in the border zone of high and low velocity anomaly area. This illustrates that the frequent occurrence of earthquake swarm or moderate earthquake in the area means the transition zone of seismic velocity underground is prone to stress conversion, energy accumulation, and instability strip in structural geology as well.