| After the discoveries of coesite-bearing eclogites in Western Alps and Norway, Sulu-Dabie becomes the largest Utralhigh-Pressure (UHP) metamorphic belt in the world. Since the middle of 1980s, many geoscientists have paid their attentions to this erogenic belt, and considered it as a natural laboratory for studying the Utralhigh-Pressure mechanism and continental geodynamics. Combining with the previous geological and geophysical data, this paper will try to describe the characteristics of the crustal structure beneath the huge UHP belt. The main results are given below:1. An imaging method, Partitioning-Variables Velocity Imaging Method in 2D Media, was put forward, and this method is applicable not only for refraction and reflection seismic data but also for complicated velocity distributions within a layer. Through model testing and analyzing, the method rarely depends on the initial velocity model, and the image will be reconstructed after just a few iterations. It will be more effective when the parameters, m and n, take appropriate values according to the geological background in the imaging area.Because of no enough information in the acquired data sets, only the shallow structures are reconstructed in this study with fine results in this dissertation.2. The 'Moveout' technique for wide-angle reflection is put forward and applied to the deep seismic sounding, especially to the reflection from the Moho, and it makes the interpretation more intuitionistic.3. The Poisson's ratio structures in Sulu and Dabie erogenic belts are obtained by using the P- and S-wave data, and make it possible to infer the composition within the crust. Generally, a lower Poisson's ratio corresponds to the rocks like felsic granite, while higher Poisson's ratio corresponds to the mafic or utralmafic rocks like basalt, and the value between the two above corresponds to the rocks like gneiss. The results from these experiments and theoretical research reveal that the silicon content in the rock is related to the velocities of P- and S-wave when they propagate through the rock, thus the composition of the crust can be infered according to the Poisson's ratio which obtained by the P- and S-wave velocities.4. The research on the Chinese Continental Deep Drilling site in the Sulu Utralhigh-Pressure Metamorphic Belt indicates that the crust can be divided into three layers. The upper crust is composed of the layers above the boundary RI, middle crust between boundaries Rj and R5, and lower crust between boundary R5 and Moho discontinuity Rm. The upper crust has a lower velocity of <6.20km/s, and is composed of 4 layers besides the Mesozoic and Cenozoic sediments. The first layer near the surface (above boundary R|) is complex rocks, and the second is deduced as the Utralhigh-Pressure Metamorphic layer. A low velocity layer with a lower Poisson's ratio of 0.23-0.235 is found between the UHP layer and boundary R3, and it probably implies a detachment or metamorphic granite intrusives. The middle crust between the boundaries Rt and R5 is of a velocity of 6.40km/s, maybe a composition of granulite or amphibolite. The velocity in the low crust is 6.60km/s with a Poisson's ratio of 0.265, and is of the characteristic of granulite. -The UHP layer takes geometry of an uplift in NS direction, becoming deep in west and shallow in east, and the depth beneath the CCDD is 2.4km with a thickness of 2.1km. The low velocity layer is 2.0km around under CCDD. The uplift is also can be found in the middle crust, corresponding to the UHP belt.The crustal thickness is 31km with an average P-wave velocity of 6.30km/s.5. The crust in Dabie UHP erogenic belt is composed of three layers without low velocity layer, according to the comprehensive research of geological and geophysical data. The shallow velocity has an obvious variation near Huoshan with a lower velocity in the north and a higher in the south. The first boundary depicts a shape of clear vertical offset there. The middle crust and lower crust are both characterized as a...
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