North China And Its Adjacent Areas Of Crust And Upper Mantle Three-dimensional Velocity Structure Of Seismic Tomography Study

The history of geophysical inversion and seismic tomography is reviewed in this paper. The tectonic of study region and the method of inversion are explained simply also. In order to get good result, the reliability and preciseness of the seismic data are analyzed carefully and the good inversion model is selected. The resolving power in this area is discussed in the end.The research region of this dissertation is 107°E-124°E and 28°N-42°N. In China geological and tectonic map, this region is referred to as the North China and some south area of it. This region is located in a seismically very active region in China. A lot of large earthquakes have occurred in it. The present study area includes many active tectonics such as Yanshan uplift, Qinling-Dabie uplift, the fault in Taihangshan piedmont, Tanlu fault ect.In total, 114971 P arrival times, 102142 S arrival times from 15714 local earthquakes, 76620 P arrive times from 4975 teleseismic events and some data from seismic sounding profile have been collected. A detailed three-dimensional(3-D) velocity model of the crust and uppermost mantle under the region is determined with a spatial resolution of 0.5° by 0.5° in the horizontal direction and 9-20 kilometer in depth. To analyze the arrival time data, we have used the tomographic method of Zhao et al.(1992). This method is adaptable to a velocity structure which includes several complex-shaped velocity discontinuities and allows 3-D velocity variations everywhere in the model. The discontinuities represent known geological boundaries, like the Moho discontinuity. A 3-D grid net is set up in model to express the 3-D structure. The tomograhic inversion was calculated using this program. According to the data distribution and several check-board tests, reliable inversion results are obtained for a model with grid size of 0.5° by 0.5° in the horizontal directions and 5 layers of 1,10,25,42 and 60 km deep from the surface to 60 km in the depth.The tomographic inversion results show that: Yanshan uplift, Qinling-Dabie uplift, the fault in Taihangshan piedmont, Tanlu fault etc are corresponding with low velocity or between low and high velocity in the crust and uppermost mantle in this region. Depth around 300 kilometer strong P-wave velocity variations of up to 4% are found in some area such as Yanshan uplift and Qinling-Dabie uplift, indicating the...