Study on Three-dimensional Crustal Structure in the Central and Southern Fujian Strait and Taiwan Strait

Author:Jin Zhen

Supervisor:Li Shan has


Degree Year:2018





The Fujian and Taiwan Straits are the most active areas of moderate strong earthquakes along the southeast coast of China.The exploration and analysis of its crustal structure model and the characteristics of the deep fault are beneficial to the research of seismogenic environment and the work of earthquake location.The study of the Crustal Dynamics in the Taiwan Strait is relatively small,and there is a lack of deep evidence based on the evolutionary process of the geological inference,and the accuracy and resolution are limited by the strain field on both sides of the Strait.In this paper,using the active and passive source observations of the Fujian and Taiwan Straits,the velocity and interface joint inversion method is used to study the three-dimensional velocity structure of the Fujian and Taiwan Straits,and to explore the shape and position of the coastal fracture zone.Based on the above analysis,the basic ideas and innovations of this paper are mainly focused on solving the following problems:1.A new method and technology for identifying the weak signal of air gun is proposed.The air gun source will encounter the air gun signal recognition problem.The reliability and accuracy of the seismic phase identification can be improved,the number of rays of the available seismic phase can be increased.We found the characteristic of low frequency bubble wave band is very narrow.It is theoretically and clearly proved that the superposition method of noise ratio does not change the phase characteristics of propagation,and this method has the characteristics of strong stability,high reliability and no interference from other noises.2.The data collection and output of active source and passive source in Fujian area.In recent years,Fujian continuously carried out deep sea exploration project,earthquake,explosion,especially the use of mobile air-guns in a reservoir and ship type air gun system,combined with the fixed network and mobile station array data generated by the Fujian earthquake 656 earthquake and artificial source seismic phase and 182252 P air-gun at sea a large number of experiments produced excitation wave phase,source and receiving phases to establish database,which lays the foundation for the research.3.A new one-dimensional standardized model of Fujian area is proposed.The wave velocity model of one dimension underground structure is not only the foundation of the initial iteration of the three-dimensional model,but also if the initial model is well chosen,Fujian early warning system would be officially released to the community after the earthquake early warning information.We extracted surface Green function by the broadband two stations with noise,the theory of surface wave and the actual surface wave Green function were compared.In this paper,a one-dimensional model of scientific explanation.4.A high resolution three-dimensional velocity model in Fujian is proposed.Land use of natural earthquake and artificial source including 22 guns blasting materials;sea use underway large capacity air-gun records,ray coverage of the chessboard grid test,to determine the optimal partition size,using one-dimensional model as the initial model,the establishment of good travel time equations by iterative technique three-dimensional velocity of P wave model got a 0.15° * 0.15° high resolution.This is a three-dimensional high precision model obtained by the first three-dimensional observation system in Fujian.5.Analysis of the large Binhai faults.The three-dimensional velocity model of Fujian area is analyzed and the analytical accuracy of different depth is studied.The analysis of the Moho surface fluctuation of the coastal fault in the land and sea transition zone is specially analyzed.It is proved that the wave velocity medium on both sides of the fault is very different,which is the deep fault of cutting the Moho surface.